Department of Pharmacy, Kings College London, UK
Cannabis plants have been cultivated in Europe, Asia, Africa and the Americas for hundreds, perhaps even thousands of years as a source of three main products— hemp fibre, cannabis seeds and medicinal or narcotic preparations (Fairbairn, 1976). Hemp fibre is obtained from cannabis stems, and has been used over the centuries for the production of textiles, rope and sacking. It is strong and durable, composed of about 70% cellulose and reaches lengths of 3-15 feet (Schultes, 1970). The fibre has been used in the past to make paper, and has been proposed as a replacement for wood pulp in modern paper production (Kovacs, 1992). However, there are many technological limitations to be overcome before this becomes a commercially viable proposition (Judt, 1995). The "seeds" (which technically are the fruit or achene) may be roasted and consumed by man, used as birdseed or anglers' bait or pressed to yield a greenish yellow, fixed oil which has been used in foodstuffs and in varnishes, paints and soap (Schultes, 1970; Fairbairn, 1976). Cannabis leaves and flowering tops and preparations derived from them have many pharmacological effects in man, including narcotic properties; the latter is the most widely known use of cannabis in the present day.
The history of cannabis is complex and it has not been possible to ascribe a precise geographical origin to the plant. The picture is complicated by a long history of human use of cannabis in many parts of the world, doubts over the distinction between wild, cultivated and escaped types, extensive transfer of its use and cultivation between cultures and the existence of much variety in the physical and chemical properties of the plant (Schultes, 1970). There is general agreement however, that cannabis is Asiatic in origin, but locations ranging from the Caspian Sea and Central and Southern Russia to Northern India and the Himalayas have been proposed as its native habitat (Schultes, 1970). Of these, an area of Central Asia just North of Afganisthan is favoured by most experts (Schultes and Hoffman, 1980).
The botanical classification of cannabis plants has been the subject of much debate and repeated alteration since the time of Linnaeus (late 18th Century). Controversy
has surrounded both the family in which the genus Cannabis is placed, and the question of whether the genus is mono—or polytypic (i.e. consisting of one or many species). A number of authors have dealt extensively with this subject (Schultes, 1970; Small and Cronquist, 1976; Schultes and Hoffman, 1980). The history of cannabis taxonomy and nomenclature is briefly reviewed in this section.
In Europe cannabis had been grown from ancient times for the production of hemp fibre. Gerarde in his 1597 Herball lists the following common European names for the plant: hempe (English), kemp (Brabanders), zarner hanff (Dutch), canape (Italian), cananio (Spanish), chanvre (French), kannabis (Greek) and cannabis (Latin). The first recorded use of the Latin binomial Cannabis sativa was by Caspar Bauhin in 1623 (Schultes, 1970), but the official publication of this name was in Linnaeus's Species Plantarum of 1753, the internationally acknowledged starting point for modern botanical nomenclature. The species name Cannabis is stated by Bloomquist (1971) to mean "canelike" whilst the genus name "sativa" has the meaning "planted or sown" and signifies that the plant is propagated from seed and not from perennial roots.
In 1785, Lamark assigned the Latin binomial Cannabis indica to cannabis grown in India, classifying it as a unique species on the basis of its different growth habit, morphological characteristics and stronger narcotic properties than the European plant. However many taxonomists regarded the plant as a variety of Cannabis sativa using the nomenclature Cannabis sativa var. indica (Schultes and Hoffman, 1980) to distinguish it from the fibre hemp. In colloquial language the term "Indian hemp" was coined and still persists as a name for narcotic cannabis.
In 1924, Janischevsky described a wild form of the fibre type of cannabis found in Western Siberia and Central Asia, which could be distinguished from the cultivated form on the morphological characteristics of the seed (achene). He assigned the domesticated or cultivated form to the species C sativa and named the wild type C. ruderalis or C. sativa var. ruderalis. Similarly, Vavilov and Bukinich (1929) described a wild form of narcotic cannabis growing in eastern Afganistan, and described this as C. indica var. kafiristanica. Thus distinctions were made based on both narcotic potential and morphological variations observed at different levels of domestication.
There are divergent views as to whether the numerous forms of Cannabis observed are variations of a single species or distinct species in their own right. An examination of entries in Index Kewensis from 1893-1990 reveals that many species, subspecies and varieties of Cannabis have been proposed during this period (C. chinensis, erratica, foetens, lupulus, macrosperma, americana, generalis, gigantea, ruderalis, intersita and kafiristanica), but that many of these have subsequently come to be regarded as equivalent to C. sativa. However many Russian botanists have held the view that several species do exist within the genus (Schultes and Hoffman, 1980). Morphological and microscopical differences between C. sativa, C. indica and C. ruderalis plants have been observed, and following extensive literature, herbarium and field studies, Schultes and co-workers at the University of Mississippi declared in 1974 their support for the Russians' view that the three should be delimited as distinct species (Schultes and Hoffman, 1980). The need to resolve the issue assumed some importance in the 1970s since the identity of cannabis samples had to be clarified for criminal proceedings against those involved in its abuse as an intoxicant. National and state laws in the
United States of America defined marijuana specifically as Cannabis sativa, and consequently any other Cannabis species could not technically be considered illegal.
The most extensive consideration of cannabis taxonomy to date is that published by Small and Cronquist in 1976. Based on an examination of the literature relating to chemical factors, plant and achene morphology, as well as the influence of selection of characteristics through cultivation over centuries, they concluded that Cannabis sativa is a single but highly variable species. Two subspecies, namely C. sativa subsp. sativa and C. sativa subsp. indica, of low and high narcotic potential respectively were proposed and each subspecies was further classified into cultivated and spontaneous (wild) varieties as follows:
C. sativa subsp. sativa var. sativa (cultivated) C. sativa subsp. sativa var. spontama (spontaneous) C. sativa subsp. indica var. indica (cultivated) C. sativa subsp. indica var. kafiristanica (spontaneous)
A taxonomic key was given to identify the four varieties, and synonyms of each listed to show relationships to previously published species names (Table 1). Further chemotaxonomic evidence for a single Cannabis species was provided by Lawi-Berger and Kapetanidis (1983) and their co-workers (Lawi-Berger et al., 1983a,b) who showed that the type and proportion of fatty acids, as well as the proteins and enzymes present in cannabis seeds from 14 different geographical locations were virtually identical.
At a higher level of classification, the genus Cannabis belongs to the family Cannabaceae (often erroneously rendered Cannabinaceae, Cannabidaceae or even Cannaboidaceae) of the order Urticales; this too has been the subject of debate. Taxonomists had initially placed the plant in Urticaceae (the nettle family), but in the early part of this Century there was some support for classifying it under Moraceae (the fig family) (Schultes, 1970). Both are families in Urticales and Cannabis has
Table 1 Synonyms of Cannabis sativa subspecies and varieties according to Small and
C. sativa Linn, subsp. sativa var. sativa Small et Cronq.
C. sativa var. vulgaris Alefield; C. chinensis Delile; C. sativa 8 chinensis A. DC.; C. gigantea Delile, C. sativa var. gigantea Alefield; C. gigantea Crevost, C. sativa ¡3 vulgaris A. DC; C. sativa y pedemontana A. DC; C. sativa var culta Czern.; C. sativa subsp. culta Serebr.; C sativa var. praecox Serebr.; C. sativa var. monoica Hol.; C. generalis Krause; C. americana Houghton et Hamilton. C. sativa subsp. sativa var. spontanea Vavilov
C. sativa var. spontanea Czernj.; C. sativa subsp. spontanea Serebr.; C. ruderalis Janisch.; C. sativa var. ruderalis Janisch. C. sativa subsp. indica var. indica (Lam.) Wehmer
C. sativa var. indica; C. macrosperma Stokes; C sativa a kif A. DC.; C. sativa forma afghanica Vav.; C. indica var. kafiristanica forma afghanica Vav. C. sativa subsp. indica var. kafiristanica (Vavilov) Small et Cronq. C. indica Lam. var. kafiristanica Vav.
some features of each, but also sufficiently significant differences to prevent it being placed with confidence in either. Morphological and chemical studies led to the creation, in the 1960s, of the distinct family Cannabaceae which contains two genera only—Cannabis and Humulus (hop plants). Table 2 shows the larger view of the taxonomical position of Cannabis within the plant kingdom, with classifications above the level of species as described by Quimby (1974) and subspecies as classified by Small and Cronquist (1976).
The establishment of the family Cannabaceae has obtained widespread support, but the debate over whether or not Cannabis is a monotypic genus has not been satisfactorily resolved. Small and Cronquist's classification is not universally accepted and support for a polytypic view of the genus still exists as evidenced by the comments of Schultes and Hoffman (1980) and subsequent entries in Index Kewensis (19761990). Nevertheless, the tendency in recent literature is to refer to all types of cannabis as Cannabis sativa L. with an indication of the fibre or narcotic characteristics of the plant. As Schultes and Hoffman (1980) point out, divergent definitions of what constitutes a distinct species are largely to blame for the controversies that have arisen in the classification of Cannabis. A second important factor is the extensive cultivation and selection of high yielding strains of the plant (fibre or narcotic) over many centuries giving rise to a wide range of phenotypes. The development of modern analytical techniques and easier access to material from different parts of the world has led to a substantial body of work on the chemical variation of cannabis plants, particularly in relation to whether the plants are predominantly fibre type or drug type, and the factors influencing this property. Chemical variation in Cannabis is discussed in more detail in Chapter 3.
Table 2 Taxonomic classification of Cannabis, (based on the descriptions of Quimby (1974)
and Small and Cronquist (1976))
Table 2 Taxonomic classification of Cannabis, (based on the descriptions of Quimby (1974)
and Small and Cronquist (1976))
C. sativa L. subsp. sativa (L.) Small et Cronquist. C. sativa subsp. indica (Lam.) Small et Cronquist.
C. sativa L. subsp. sativa (L.) Small et Cronquist var. sativa (L.) Small et
Cronquist, Taxon 25 (1976) 421. C. sativa L. subsp. sativa (L.) Small et Cronquist var. spontanea Vavilov,
Taxon 25 (1976) 423. C. sativa L. subsp. indica (Lam.) Small et Cronquist var. indica (Lam.)
Wehmer, Die Pflanzenstoffe (1911) 248. C. sativa L. subsp. indica (Lam.) Small et Cronquist var. kafiristanica (Vavilov) Small et Cronquist, Taxon 25 (1976) 429.
Despite the debate over the mono or polytypic status of the genus Cannabis, all cannabis plants are easily recognised by certain distinct common botanical characteristics. Early herbals (Dodonaeus, Gerarde) speak of two types of cannabis— the seed bearing type and the barren type, which reflect the fact that the plant is dioecious i.e. that it bears male and female flowers on separate plants (Figure 1). The male plant bears staminate flowers and the female plant pistillate flowers which eventually develop into the fruit and seeds. In the early herbals the sexes were in fact erroneously assigned, with the plant bearing seeds referred to as seede hempe, male hempe or Cannabis mas and the plant bearing flowers alone referred to as barren hempe, female hempe or Cannabis femina.
Occasionally monoecious plants are encountered bearing both male and female flowers; these may arise as a result of special breeding (Small and Cronquist, 1976). They are particularly frequent in varieties developed for hemp production (Clarke, 1981). Feminisation of male plants using ethephon (Ram and Sett, 1982a) and masculinisation of female plants with silver nitrate and silver thiosulphate complex (Ram and Sett, 1982b) have been reported, and irradiation (Nigam et al., 1981a) or treatment with streptovaricin (Nigam et al., 1981b) can also induce changes in flower formation. An interesting observation was that in a collection of wild cannabis plants
growing along streets and highways in the United States, only 41% were male as compared to 55% of all plants collected from varying sites for the study (Haney and Bazzaz, 1970). It has been demonstrated (Heslop-Harrison, 1957) that exposure to low levels of carbon monoxide for short periods of time can cause a shift of sex expression from male to female.
Information published elsewhere (Stearn, 1970; Schultes and Hoffman, 1980; Bloomquist, 1971; Clarke, 1981: pp. 1-10), gives detailed technical descriptions of cannabis morphology; the information has been simplified in the present text. Cannabis plants have tap roots, about one-tenth the length of the stalk, and with small branches diversifying out from the main root. Above ground, the plants vary in height from 1-20 feet (1-6 m). Up to the flowering season, plants of both sexes have a similar appearance, although the male plants may be more slender than the females which tend to be somewhat stocky. The stems are angular and furrowed, sometimes hollow and can be either branched or unbranched, depending on the proximity of neighbouring plants. Both sexes have compound, green leaves composed of 3-15 leaflets or blades with toothed margins. The leaflets are arranged in a palmate fashion, i.e. radiating from a single point at the end of a stalk. At the base of the stem, the leaves are arranged in pairs, but this changes to an alternate, spiral arrangement, generally with an increasing number of leaflets in the upper parts. The leaflets are 611 cm long and between 2 to 15mm wide. Variations in leaf shape within this broad description have been recorded (Clarke, 1981: p. 89).
Often the sex of the plant is only determinable at the onset of flowering, when the distinct male and female flowers emerge. The two types of inflorescence are easily distinguished. The male inflorescence is composed of many individual flowers borne on flowering branches up to 18cm long and stands out from the leaves. The individual flowers are small, consisting of 5 whitish or greenish sepals less than 5 mm in length and containing 5 pendulous stamens. By contrast the female inflorescences, do not project beyond the surrounding leaves and are formed in the axillae or terminals of branches. They are compact, short and contain only a few flowers grouped in pairs. Each flower consists of an ovary surrounded by a green bract (the calyx) which forms a tubular sheath about 2mm in length around the ovary. Two stigmata project out of this sheath. Following fertilisation, the ovary (containing a single ovule) develops into a thin wall surrounding a single seed with a hard shell. This sort of fruit is technically termed an achene, In practice the whole fruit is regarded as the "seed" known as hempseed or cannabis seed. The achene is 2.5-5 mm long and slightly less in width.
Virtually every aerial part of the cannabis plant is covered in minute hairs or trichomes. These are either simple hairs (covering trichomes) or glandular trichomes (Figure 2) containing a resin. Five main types of trichomes have been identified (Fairbairn, 1976; Turner et al., 1981a) and described (Clarke, 1981: p. 97). These are:
(a) long, unicellular, smooth, curved, covering trichomes;
(b) more squat, unicellular, cystolith covering trichomes, containing calcium carbonate;
(c) bulbous, glandular trichomes;
(d) capitate-sessile (i.e. without a stalk), glandular trichomes, and
(e) capitate-stalked, glandular trichomes.
Types (a)-(d) are found on the vegetative leaves and pistillate bracts, while type (e) is found on the bracts and floral leaves only (Hammond and Mahlberg, 1977; Turner et al., 1981a). The capitate glandular trichomes have been shown to contain cannabinoids, the unique phytochemicals found in cannabis, some of which are responsible for the intoxicant properties of the plant (Fairbairn, 1972; Turner et al., 1977, 1978). Within the trichomes, the cannabinoids form a resinous substance. This is present in secretory sacs which consist of a distended area bounded by a sheath, formed between secretory cells of the trichome (Lanyon et al., 1981). Cannabinoids are not found in the non-glandular (covering) trichomes (Malingre et al., 1975).
It has been shown that the density of capitate sessile and bulbous glands on the pistillate bract decreases as the bract matures, whereas that of capitate stalked glands increases (Turner et al., 1981b). In leaf development however, bulbous and sessile capitate gland density remains virtually unchanged (Turner et al., 1981a). In both leaves and bracts, the density of non-glandular trichomes show an overall decrease in density over time (Turner et al., 1981 a, b). A comparison of the cannabinoid content and total numbers of glands in the two organs reveals differences. During bract development, the total number of capitate glands, total cannabinoid content and cannabinoid content per unit dry weight increases (Turner et al, 1981b). However, in the leaf, although total numbers of capitate glands and total cannabinoid content per leaflet increase, the concentration of cannabinoids decreases during leaf maturation
(Turner et al, 1981 a). These studies further strengthen the association between the glandular trichomes and cannabinoid content.
Glandular trichomes of cannabis have been used as a diagnostic agent in identifying the plant material by microscopy when more gross morphological characteristics are not discernable (e.g. in a fragmented leaf). Corrigan and Lynch (1980) have carried out extensive experiments to find a suitable staining agent which will allow cannabis to be distinguished from other plant materials that may have trichomes of a similar appearance. Fast Blue B was found to be a highly selective stain for the cannabinoids in the trichomes of Cannabis sativa, having no effect on the trichomes of over two hundred other plant species tested. The stalked capitate trichomes of the bract have a characteristic appearance, being 130-250 m in length, and having either a multicellular or unicellular stalk and 8-16 cells in the head (Evans, 1989; Bruneton, 1995). The cystolithic covering trichomes of cannabis, although unusual, are not sufficiently unique to the species to be of diagnostic value (Thornton and Nakamura, 1972).
Cannabis is an annual herb, which grows during the warm season, and then dies down, with new generations springing up from seed the following year. It can grow in any sort of soil, even when nutrition is poor (Bloomquist, 1971), although for commercial purposes good soils are required since cannabis is a heavy feeder and can deplete the soil of nutrients (Schultes, 1970). It has been observed that mature seeds from domesticated varieties of cannabis are larger and germinate more readily than those of wild plants (Janischevsky, 1924). Seeds usually germinate within 3-7 days of sowing (Clarke, 1981: p. 1), and under favourable conditions, the height of the plant can increase by as much as 7 cm per day (Clarke, 1981: p. 2).
Flowering is usually initiated at a critical daylength (photoperiod), which varies depending on the strain of the plant (Clarke, 1981: p. 3). As cannabis is usually dioecious, male and female flowers are produced on separate plants and pollination is reported to occur mainly by the agency of wind (Bloomquist, 1971). The male plants die down soon after pollination whilst the females survive until the onset of inclement weather (frost in temperate areas and drought in the tropics). However, female plants kept indoors are reported to survive for many years (Anon., 1972). Seeds mature towards the end of the warm season and both man and birds are important in their dispersal (Haney and Bazzaz, 1970).
The maturation time for cannabis varies from two to ten months (Anon., 1972). Typically in the Northern hemisphere, cannabis seeds would be sown in May and the plants harvested in September (Bloomquist, 1971). Brenneisen and Kessler (1987), studying cannabis cultivation in Switzerland, have described early and late maturing ecotypes of cannabis. Early maturing forms ("Bolivia" and "Italia") generally originate in temperate zones or at higher altitudes in the subtropics e.g. from the Andes, Atlas, and Himalaya mountain ranges where vegetation time is limited. They have thick and feather-like leaves. Female flowers are produced in mid August, with male flowers appearing four to eight weeks before this. Maturation of the fruit occurs from mid-September to mid-October. The late maturing ecotypes ("Hellas", "Africa I" and
"Africa II") originate from tropical or subtropical zones such the Caribbean, Central America, California, Africa and Asia. They have thinner leaves, and produce flowers between mid-September and the end of October. They can only be made to bear mature fruit in European countries if grown under artificial heat and lighting conditions. The pattern of production of A9-tetrahydrocannabinol (THC), the main narcotic cannabinqid, also differs in the two ecotypes. In the early maturing forms, THC concentrations in the plant are relatively low initially and peak at the time of seed ripening. By contrast, levels of THC in vegetative parts of the plant are generally higher in the late maturing types, peak towards the end of the vegetative growth and begin to decrease in the reproductive phase. This latter type is favoured by growers seeking to produce cannabis for narcotic purposes. Rosenthal (1984) has reviewed the maturation period and general characteristics of narcotic cannabis varieties from around the world.
Cannabis is reported to have few natural enemies other than man (Bloomquist, 1971). It is generally resistant to weather change, although heavy frosts may destroy it. Established cannabis plants are able to control the growth of competing weeds, possibly through the agency of volatile terpenes and sesquiterpenes produced by the plant (Haney and Bazzaz, 1970). Young cannabis plants are unable to produce terpenes and may become smothered by surrounding weeds if not controlled. Pests attacking cannabis include the root parasite, branched broom rape, which has been known to cause some damage in European plants (Haney and Bazzaz, 1970). In India, young plants of the drug crop are reported to be prone to wilt disease caused by Sclerotium rolfsii Sacc. whilst the hemp crop may suffer leafspot disease caused by Phomopsis cannabina Curzi, and infestation by cut worms (Anon., 1992).
CULTIVATION OF CANNABIS History of Cannabis Cultivation
The histories of the main uses of cannabis can be traced separately but are inevitably linked as a result of the intermingling of knowledge from diverse cultural streams. Archaeological evidence suggests that the use of cannabis can be traced back at least 6000 years (Anon., 1972) and specimens have been found in a 3000-4000 year old Egyptian excavation site (Schultes, 1970).
Schultes (1970) states that cannabis as a source of hemp fibre was probably introduced into Western Europe from the East at different times and by different invaders. Hempen cloth, estimated to have survived from about 6000 years ago, has been excavated from sites in Europe and samples of hemp seeds, leaves, textiles and rope dating to between 500 BC and 300 AD have been found in Germany and England (Schultes, 1970). Pollen evidence shows increasing cultivation of cannabis in England from the early Anglo-Saxon era to the Norman period (Godwin, 1967). The cultivation and processing of hemp in eastern England during medieval times is also suggested by pollen and fossil evidence (Bradshaw et al, 1981). The fibres were apparently obtained by a process known as "water-retting" in which bundles of mature stems were placed in deep ponds of standing water (retting pits) to allow rotting of the tissue surrounding the fibres (Bradshaw et al., 1981). There is evidence for similar cultivation and processing of cannabis in Central Wales during the Tudor period (French and Moore, 1986).
The cultivation of hemp spread to the Americas following the influx of European colonists. It was introduced to South America by the Spanish in 1545, to Canada in 1606 by Louis Hébert, apothecary to the French explorer Samuel de Champlain (Anon., 1972), and to New England by the pilgrims from England. Hemp cultivation in North America was actively encouraged by both France and England in order to supply both European and local American demand. By 1630, cannabis had become a staple crop on the East Coast of North America. Thus until relatively recently, the predominant use of cannabis in the West was as a source of hemp, with the narcotic and medicinal uses only being recognised following contact with Asian and Northern African cultures to whom these properties were well known (Kalant, 1968).
In Asia, the pharmacological effects of cannabis had been discovered in ancient times and the plant was used for medicinal, narcotic and ceremonial purposes. Early writings (Anon., 1972) on the effects of the herb include the medicinal treatise of the legendary Chinese Emperor, Shen Nung (ca 2700 BC, although there is some dispute about the date and authorship of the text), the ancient Atharvaveda of India (pre 1400 BC) and the Zend-Avesta of Northern Iran (ca 600 BC). Herodotus (ca 450 BC) described the use of cannabis in funeral rites of the Scythians, who occupied an area near the Black Sea. The herb (Emboden, 1972) or seeds (Schultes, 1970) were thrown onto heated stones and the vapour inhaled as a post-funeral purification rite. A similar method of use has been reported in the pre-Portuguese era among people living in the Zambezi valley of Africa, where vapours from a smouldering pile of cannabis would be inhaled either directly or through reeds. The incorporation of cannabis-based rituals into important social ceremonies is believed by some anthropologists to indicate a long period of contact with the herb. The use of cannabis as an euphoriant is thought to have spread from India to the Middle East and then to North Africa (Kalant, 1968).
Although Galen (130-200 AD) recorded the intoxicating effects of excessive consumption of hemp cakes (Schultes and Hoffman, 1980), in Western Europe the narcotic properties of cannabis do not appear to have been widely known until relatively recently. The German Schoffer in the "Latin Herbarius" of 1474 lists numerous medicinal uses such as clearing scales from the head, growing hair, aiding digestion, analgesia and drying up the sperm, but makes no mention of any psychoactive effects (Nigg and Seigler, 1992). The herb does not appear at all in Herba Plantes by Sanitatis (1491), but by the next Century can be found listed either as "hempe" or "cannabis" or "cannabina herba" in herbals by Dodonaeus (1578) and Gerarde (1597, 1633). Neither of these authors makes any mention of the narcotic properties of the herb, but list similar uses to Ortus Sanitatis as well as the intriguing use of the herb to increase egg laying in hens! It is thought (Kalant, 1968) that it was only in the 19th Century that the euphoriant properties of cannabis were learnt of by the British in India, and the French in North Africa. The infamous "Club des Hachischins" founded in Paris in 1844 gained a small European following who experimented with the narcotic effects of the herb (Anon., 1972; Bergel and Davis, 1970) but the widespread use of cannabis for hedonistic purposes in Western Europe is believed to be more recent (Anon., 1972), following the popularisation of American practices of the early twentieth Century.
It is believed that cannabis (origin unknown) was already being used as a narcotic in Central and South America in the 16th Century (Anon., 1972), when it was introduced for hemp production by the Spanish. Knowledge of its narcotic properties in Brazil however, was said to have spread only following the arrival of slaves from Africa who were already familiar with its use (Anon., 1972). The Mexicans are credited with the dissemination of this knowledge to English-speaking North America between 1920 and 1930 (Kalant, 1968). The hedonistic use of the herb spread so rapidly in North America, both in the criminal underworld and in fashionable circles, that even by the mid-1930s there was considerable official concern both about the dangers to the user and its connection with criminality (Bergel and Davis, 1970). At present, in the majority of countries of the world, cannabis cultivation and use for narcotic purposes is a criminal offence. Nevertheless there is widespread illicit cultivation of the plant and an international trade in narcotic preparations derived from it.
The history of the medicinal use of cannabis mirrors its narcotic use, although the herb possesses numerous other pharmacological properties. Cannabis appears in ancient Chinese and Indian works on medicine and features in the 15th and 16th century Western herbals. In Medieval Europe, preparations made from the root or seed of hemp cannabis were used for gout, cystitis, gynaecological problems and various other conditions, some of which have been listed above (Le Strange, 1977). However, the superior medicinal properties of the Indian variety of cannabis were recognised by W.B.O'Shaughnessy, a British physician working in Calcutta, who is believed to have introduced the herb to Western medicine. His report in 1842 on the analgesic, anticonvulsant and muscle relaxant properties of the drug generated much interest and led to its widespread use in the 19th Century. It became a recognised official drug, featuring in a number of Pharmacopoeias. Despite extensive cultivation of cannabis in Europe and America, the principal variety used in official medicines came from India (Le Strange, 1977). However, from the beginning of the 20th Century, the popularity of cannabis preparations declined due not only to the variable properties and erratic availability of the plant, but also as a consequence of the emergence of more reliable synthetic medicaments without narcotic effects. Cannabis was removed from the British Pharmacopoeia in 1932, The United States Pharmacopoeia in 1942 and the Indian Pharmacopoeia in 1966.
Although medicinal use of cannabis has declined, its popularity as an euphoric narcotic has continued to increase to the present day, especially among the younger generation. In recent years, there has been much social debate about the legal position of cannabis use, with many calling for its decriminalisation on the grounds of its low addictive potential and its non-narcotic pharmacological properties which could still make a valuable contribution to modern medicine (Gray, 1995).
Cannabis is now widely distributed throughout the world, both in cultivated forms and as wild plants escaped over the years from cultivation sites. Large scale commercial production takes place in relatively few areas and a distinction can be drawn between its legitimate cultivation as a source of hemp fibre and seeds and the usually illicit cultivation of cannabis as a source of narcotic materials. Whether a cannabis plant predominantly produces fibre (hemp) or narcotic resin is governed by both genetic and climatic factors (see Chapter 3). However, in general terms it can be said that the two properties seem inversely related and individual varieties can be classified as either drug type or fibre type (Bruneton, 1995) depending on the concentrations of the psychoactive compound THC and the non-narcotic cannabinoid, cannabidiol (CBD). The "drug" or "resin" type has a high THC concentration (>1%) and virtually no CBD. This property is observed amongst plants growing in warm climates and producing abundant narcotic resin. The "fibre" or "hemp" type, grown in northern temperate zones has very low THC levels (<0.3%, or even<0.03% for most cannabis varieties cultivated for fibre) and high CBD concentrations. However "intermediate" varieties are also found, with high levels of both THC and CBD. The general growth cycle of plants from the different varieties is similar, except for variations in maturation period (Clarke, 1981: p. 124) although the forms selected, harvesting methods and further processing depend on the purpose for which the plant is cultivated. The breeding and cultivation of cannabis plants with different characterisitics have been described in detail by Clarke (1981).
Cultivation of Cannabis for Hemp Fibre or Cannabis Seed
Despite its widespread cultivation in Europe and North America in the late 19th and early 20th centuries, the large scale production of hemp for fibre or seed is now restricted to a few areas of Eastern Europe (Hungary, Romania, Ukraine, Russia, former Czechoslovakia, Serbia, Croatia) and China (De Meijer, 1995). This is partly due to a great reduction in the demand for hemp fibre following the advent of more attractive alternatives (synthetic or natural), and secondly due to concerns and restrictions throughout the world on the cultivation of cannabis for narcotic purposes. Since 1961, the cultivation, trade and consumption of cannabis have been placed under restrictions worldwide following the United Nations Organisation's "Single Convention on Narcotic Drugs" (Brenneisen, 1983).
Whilst cultivation of drug type cannabis is universally prohibited or legally regulated, rules concerning cultivation of fibre (hemp) forms vary. In Canada, for example, the cultivation of any cannabis without special authorization has been prohibited since 1938, and all hemp fibre used in the country has to be imported (Anon., 1972). De Meijer (1995) has reviewed the availability and registration status of hemp cultivars in Europe. A number have been registered by the European Union (EU), which implies that their cultivation should be permitted by any member state. In practice, individual states may obstruct seed distribution and cultivation on a number of grounds including national drug legislation. In Italy, for instance, hemp cultivation is prohibited as long as a cultivar cannot be identified with a morphological marker linked to low THC-content (De Meijer, 1995). However, in France, a 1990 statute specifies 12 fibre varieties with not more than 0.3% THC which may be cultivated for the manufacture of speciality papers, non-woven products, furniture particle board, animal litter and so on. The producers must hold a contract specifying a buyer and use certified seeds from the authorised varieties (Bruneton, 1995). Cannabis is also legally cultivated for fibre and seed in Switzerland (Brenneisen, 1983).
There has been considerable recent interest in the development of hemp as an industrial crop in the Netherlands (De Meijer and Van Soest, 1992). Under the National Hemp Programme, the Centre for Plant Breeding and Reproduction Research (CPRO) have carried out a number of studies surveying variations in cannabis cultivars in terms of stem yield and quality, psychoactive potency, resistance to root-knot nematodes and plant morphology (De Meijer and Keizer, 1996), principally to evaluate their suitability as an arable source of paper pulp. A germplasm collection has been established at CPRO (De Meijer and Van Soest, 1992).
Fibre type cannabis is best grown in cold or temperate regions where the subsoil is moist and rain is abundant, since fibres produced in hot, dry climates are too brittle to be of commercial value (Bloomquist, 1971). The use of well-manured soil is recommended since this improves the quality of the fibres (Schultes, 1970). Commercially produced, high fibre varieties of even maturation time are selected to facilitate efficient harvesting. These are often monoecious strains which tend to mature more evenly than dioecious ones (Clarke, 1981: p. 15). Hemp bast fibre is produced in the phloem tissue of the stem. Consequently, the plants are grown close to each other so that branching is limited and long slender stems are produced (Fairbairn, 1976). The properties of hemp fibre, its harvesting and processing have been described by Judt (1995) and Clarke (1981: p. 150). Two types of fibres are present in cannabis stems—bark or bast fibres (23-28% by weight) and core fibres (75-70%). The two vary in their physical characteristics and chemical composition (Judt, 1995). Bark fibres are 20-22mm long and contain nearly 70% cellulose and small amounts of hemicellulose (10%) and lignin (5%). Compared to these, core fibres are considerably smaller in length (0.55mm) and have a lower proportion of cellulose (35%) and greater amounts of hemicellulose and lignin (20% of each).
Cannabis stalks are harvested at a point in the plant's growth (usually a prefloral stage) most appropriate to the best yield of fibre, before extensive lignification sets in (Clarke, 1981: p. 150). This is often a critical matter of a few days (Judt, 1995). A portion of the crop may be left to develop mature seed which can be used the following year. The harvested stalks are stripped of leaves, dried and stored in bales before further processing. Whole stalks may be pulped by chemical or mechanical means to obtain a heterogenous mix of fibres, whilst bast fibres may be separated by a process known as retting—partial rotting of the stems in water to destroy the other parts of the plant (Clarke, 1981: p. 150). Natural retting takes from a week to a month. The fibres are then dried, wrapped in bundles and stored in a cool, dry area.
Hemp fibre is relatively expensive to produce; in a study carried out in 1994 (Judt, 1995) to determine the viability of using hemp in the paper industry, the suggested prices of whole hemp stalks and the more valuable bast fibre were US $200 and US $630 respectively per air-dry ton as compared with US $78-199 for hard-wood pulp.
When the seeds are required as the commercial product, plants are cut only after seed maturation. Seeds fall easily from the floral clusters when mature and may be collected by hand or machine. The remainder of the plant may be used as pulp material (Clarke, 1981: p. 150).
Cultivation of Cannabis for Narcotic Use in India and Surrounding Areas
In Asia, cannabis grows wild throughout the Himalayas from Kashmir to Eastern Assam, up to altitudes of 10,000ft (Chopra et al., 1958). It extends down into parts of Pakistan, Bangladesh and India (Punjab, Bengal, Uttar Pradesh and Bihar) but in many of these areas, it is possible that wild growth of cannabis is supplemented by human factors arising from local use of the herb (Chopra et al., 1958; Evans, 1989). There are a few licensed growers of cannabis in Madhya Pradesh and Orissa (Anon., 1992), but illicit cultivation of cannabis is widespread not just in India, but throughout the tropical and sub-tropical areas of the world.
Due to its long historical association with the medicinal and narcotic use of cannabis, cultivation and harvesting practice in India is well documented (Chopra et al., 1958; Anon. 1992). Seed is sown in rows about 1.3m apart in rich, well-manured, weed-free soils; light or loamy soils are preferred (Evans, 1989; Chopra et al., 1958). Sowing takes place in June or July and harvesting in December or January. When the plants reach a height of about 20cm, they are thinned out and the lower branches removed to stimulate growth of the flowering branches. The narcotic components of cannabis (mainly THC) are found in a resin secreted by glandular trichomes on the leaves and flower bracts, particularly on pistillate flowers (Clarke, 1981).
In some areas, the tradition is that, as soon as flowering begins, the male plants are identified and systematically removed by the roots (Bloomquist, 1971). A common belief that the male plants are pharmacologically inactive is not true since similar amounts of cannabinoids may be produced in plants of either sex (Chiesa et al., 1973; Valle et al., 1968). However, male plants often yield less plant material, and the staminate bracts have fewer glandular trichomes than the pistillate ones (Clarke, 1981). It has further been shown that buds from unfertilized flowering tops of female plants are more potent (i.e. contain higher THC levels) than fertilised buds, and may even exceed some resin samples in cannabinoid content (El Sohly et al., 1984). When unpollinated, the pistillate plants start to produce more capitate glandular (resin producing) trichomes probably as a protection for the unfertilised ovule (Clarke, 1981). The product consisting of unfertilised flowering tops is referred to as "sinsemilla", derived from the Spanish words "sin" (without) and "semilla" (seed) (Rosenthal, 1984). It is highly valued not only for its greater potency, but also for its more intense aroma and enhanced appearance (Rosenthal, 1984).
To obtain sinsemilla, it is imperative that the male plants are removed meticulously before any large flower clusters appear, since even a single male flower is capable of yielding sufficient pollen to fertilise a large number of females. Male flowers growing in plant internodes can be used to to distinguish them from females at an early stage of their development (Rosenthal, 1984; Clarke, 1981). However, this practice requires much care and attention and the removal of male plants to produce sinsemilla buds is generally carried out only in small cultivation sites (El Sohly et al., 1984). Consequently seeds are commonly encountered in many of the commercial cannabis products (Baker et al., 1980b).
When grown for narcotic or medicinal use in India, the main parts of the cannabis plant harvested are the leaves, female flowering tops or the resin itself. Different harvesting and processing methods are used depending on the final product required
(Chopra et al., 1958; Anon., 1992). Bhang consists of larger leaves and twigs of the plant and is prepared by simply cutting the plants (wild or cultivated), drying them and beating them against a hard surface to separate the leaves. Both male and female plants may be used (Evans, 1989) and flowering parts are frequently present. Ganja or gunja consists of the dried flowering and fruiting tops of the female plant from which the resin has not been removed. Harvesting for ganja begins when the lower leaves begin to turn yellow. Spikes bearing the inflorescences are cut off and taken to the manufacturer's yard. For Bombay ganja, the plant material is piled into ridges and furrows and the material subjected to repeated treading by foot, turning over, drying and retreading. This results in the formation of compact sheaves which are made into piles and kept under pressure for a few days. The heaps are turned over, spread again and the treading repeated. The material is sifted to separate out dust, stones, seeds and leaves and then packed into a flat cake. For Bengal ganja, the withered flowering tops are not trampled on, but rolled by hand or foot to form rounded or sausage shaped masses.
According to Clarke (1981: p. 152), flowering tops or floral clusters are best dried by hanging the plants or clusters upside down, a method practised by some growers. This has the effect of allowing the leaves to hang next to the clusters and protect them from mechanical damage which may cause loss of the resin. The method also serves to enhance the appearance of the clusters when dry, since they appear larger than if they are compressed by laying flat to dry. During the drying process, the characteristics of the leaves and flowers change in that the unpleasant "green" taste of the cannabis is gradually lost in a process known as "curing". This does not happen if drying occurs too rapidly. However, too slow or incomplete drying may lead to deterioration of the plant material by the agency of micro-organisms (Clarke, 1981: p. 153). Removal of the outer leaves from the dried floral clusters known as "manicuring". Manicuring before drying may result in loss of resin potency due to greater breakdown of THC (Clarke, 1981: p. 153).
Another Indian product charas (or churrus) is the actual resin, in crude form, from the leaves and flowering tops. Men dressed in leather suits, jackets or aprons walk through the fields rubbing and crushing against the plants in the morning shortly after sunrise. The resin exuding from the leaf and flower trichomes sticks to the leather and can be scraped off (Samuelsson, 1992). Other methods include rubbing the flowering tops with the hands, from which resin is later scraped off, beating the flowering tops over a piece of cloth on which the resin collects as a greyish powder, or thrashing the tops against smooth concrete walls and collecting the powder and resin that stick to the wall (Samuelsson, 1992; Chopra et al., 1958).
Bhang, ganja and charas have been in use for many centuries in India. The dried and crushed flower heads and small leaves (ganja) from any geographical source, are commonly referred to as marijuana and the resin (charas) is referred to as hashish. Other names encountered for the different types of cannabis products described above are discussed further on in this chapter. Relatively recently, a further product of cannabis has entered the illicit market and is a concentrated liquid extract or oil produced by hot-solvent extraction or distillation of the resin (Brenneisen, 1983), or occasionally similar treatment of the herb or flowering tops (Baker et al., 1980b). Three to six kilograms of resin are needed to produce one kilogram of oil (Stamler et al., 1985), which may subsequently be dissolved in a vegetable oil (Anon., 1992).
The product contains high levels of THC and is commonly referred to as hash oil. This is not to be confused with cannabis seed oil which is a fixed oil devoid of narcotic properties.
The international trafficking of cannabis products is mainly supplied from a few major source countries in tropical or sub-tropical areas of the world. Products originating in India or Pakistan are often seized by Customs officials, but other equally important producers are Colombia, Mexico, Jamaica, Morocco, Lebanon and Thailand (Bruneton, 1995; Stamler et al, 1985; Brenneisen and El Sohly, 1988). However, since this illicit trade is a lucrative one, smaller seizures of cannabis products originating from diverse parts of the world are encountered. These include other South American and Caribbean countries, Southern parts of North America, Egypt, Turkey and Nepal as well as various non-Mediterranean African countries viz. Ghana, Nigeria, Sierra Leone, Kenya, Zaire, Malawi, Zambia, Zimbabwe and South Africa (Baker et al., 1980a, b; 1982). Different strains of cannabis are grown in these locations, and consequently, the gross phenotype of the cannabis plants can vary from the short, broad strains of the Hindu Kush to tall meandering varieties found in Thailand (Clarke, 1981; pp. 102-118). Chemical characteristics of plants from different geographical origins are also known to vary (see Chapter 3).
As well as large scale cultivation in the aforementioned tropical or sub-tropical regions, a proportion of the cannabis used for hedonistic purposes is cultivated by individuals in temperate end-user countries either for personal use or supply. Indoor or greenhouse cultivation, which has been described extensively by Rosenthal (1984), reduces the problem of poor resin potency due to low outdoor temperatures and minimises the risk of detection by law-enforcement agencies (Stamler et al., 1985). Photoperiod can be controlled with the use of, for example, blackout screens in order to force flowering (Clarke, 1981, p. 148). Growth from seed can be successful, but in many of these illicit operations, vegetative propagation is carried out from stem cuttings of female plants, firstly in order to speed up propagation and secondly to ensure the sex of the plant. The cuttings may be grown either in soil or hydroponically, often without roots (Rosenthal, 1984). Hydroponic propagation of stem cuttings has the legal advantage, in the United States of America for instance, that the cutting is not classed as a "plant" if it lacks roots (Taylor et al., 1994). This assumes significance where the severity of sentencing is based on the total count of "plants" in the defendant's possession. As well as indoor cultivation of cannabis plants, clandestine small scale operations in Canada for producing hash oil have also been reported (Stamler et al., 1985).
ILLICIT CANNABIS PRODUCTS
The main illicit products of cannabis plants are female flowering tops with or without leaves, the resin from the flowering tops and an oil extracted or distilled from the resin, or more rarely, directly from the leaves and flowering tops. Many names are in use for these products in different parts of the world.
Preparation of the leaves and flowering tops are generally referred to in English speaking countries as cannabis, Indian hemp or very often marijuana (sometimes rendered marihuana). Various etymological sources suggested for the latter name include the Mexican-Spanish mariguana or Portuguese mariguango meaning "intoxicant", the Mexican-Spanish slang Marijuana (Mary-Jane) or Maria y Juana (Mary and Jane), or an earlier Aztec word milan-a-huan (Bloomquist, 1971). Names in other parts of the world include bhang (India, leaves) ganja or gunja (India, Jamaica, flowering tops), kif or kief (Morocco), dagga (Southern Africa), maconha (Brazil), kabak (Turkey), and rarely hashish (Egypt) although this latter name usually refers to the resin. Common slang names in the West include grass, pot, dope, weed, Mary Jane, hash and less often, shit, bush, tea, Texas tea, locoweed, griefo, hay, hemp, jive, mor-a-griefa, rope, boo, wacky backy, or black (Bloomquist, 1971; Anon., 1972; Bergel and Davies, 1970; Gosden, 1987).
Cannabis resin, known as charras or churrus in India is almost universally referred to as hashish. The word has in many texts been linked to the terms "ashashin" or "hashashi" (hashashan=herb eaters), fanatical religious followers of an 11th Century Persian leader, known to the Crusaders as the Old Man of the Mountains (Bergel and Davis, 1970; Anon., 1972). It is said that their political and military activities led to their name forming the root of the English word "assassin", whilst their connection with the use of cannabis formed the basis of the derivation of "hashish". This linguistic derivation is under some dispute, and it has been said that the Arabic word "hashish" which means "dry herb", "grass" or even "hemp" is a far more likely origin (Anon., 1972). Slang names for the resin include hash, shit and stuff (Brenneisen, 1983). The oil obtained from cannabis resin is known as hashish oil or more commonly hash oil (Gosden, 1987). Slang names include oil, red oil, and Indian oil (Brenneisen, 1983).
Cigarettes containing marijuana, hashish or hash oil, are known as reefers on joints (Wills, 1993), and plastic bags containing leafy plant material, usually with seeds present are known as a stash (Bloomquist, 1971).
International Trafficking of Illicit Cannabis Products
Stamler et al. (1985) have reviewed the local geographical sites of production within the major source countries, as well as local cultivation, storage and trafficking practices. For example, two annual harvests are obtained in Colombia, and there is evidence that crops are staggered in order to ensure a continuous supply. Generally, the crop is cultivated by individual farmers and sold to drug traffickers who may also cultivate the plant. The cut and dried plants are packaged in 20-35kg bundles and transported by mule to clandestine airstrips or more commonly beaches. Maritime rather than airplane transport is common in the illicit supply of Colombian marijuana which is more frequently encountered in North America than in Europe. Sea routes are often used by smugglers operating from Mediterranean sources and Thailand, whereas hashish smuggling from India and Pakistan is usually done on a small scale by couriers travelling on commercial airlines. Small quantities of cannabis products may also be sent between countries via the normal postal service.
Drug trafficking patterns are subject to change over time (Stamler et al., 1985), influenced no doubt by political factors in source countries as well as the work of customs and police officials worldwide. There is also evidence that cannabis products from one source country may be shipped to their eventual destination via an intermediate country, itself perhaps involved in cannabis cultivation. For instance, Colombian or Thai cannabis may be transported through Mexico to the United States (Brenneisen and El Sohly, 1988), whilst the geographical location of Jamaica makes it an important storage and forwarding site for the drugs from other sources (Stamler et al., 1985).
The predominant type of product supplied may differ from country to country. Countries such as Colombia, Mexico, Bolivia, Thailand and the non-Mediterranean African countries generally supply only marijuana, whereas in addition to marijuana, hashish and hash oil are produced in Morocco, the Middle East, India and Pakistan (Brenneisen, 1983), and Jamaica (Stamler et al., 1985).
Cannabis products from different parts of the world vary in appearance not only due to variations in plant characteristics, but also processing methods and packaging. A range of these products is shown in Figures 3-5. El Sohly et al. (1984), Baker et al. (1980a, b) and Brenneisen (1983) have described some visual characteristics indicative of the geographical origin of cannabis products. Marijuana for instance can sometimes be obtained in the form of loose plant material consisting of various combinations of
Figure 3 Cannabis products from around the world. Top row, left to right: Indian, Lebanese, Turkish and Pakistani hashish. Bottom row, left to right: Swiss hashish, Zairean marijuana, Swiss marijuana, Morrocan hash oil. Photograph courtesy of Professor R.Brenneisen, University of Bern
Figure 3 Cannabis products from around the world. Top row, left to right: Indian, Lebanese, Turkish and Pakistani hashish. Bottom row, left to right: Swiss hashish, Zairean marijuana, Swiss marijuana, Morrocan hash oil. Photograph courtesy of Professor R.Brenneisen, University of Bern
dried leaves, stems and seeds, with the colour varying from shades of green to brown depending on the source country (Baker et al., 1980b). However, a classical Mexican packaging method is to compress the plant material into a block or kilobrick, whereas marijuana from Thailand is obtained as "Thai sticks" (Figure 4) consisting of leafy material tied around stems (El Sohly et al., 1984). Sinsemilla is obtained as loose flowering tops characterised by the absence of seeds (El Sohly et al., 1984).
Cannabis resins (hashish) from Mediterranean countries are characteristically powdery and pale green or brown whereas those from India, Nepal and Pakistan are much darker, varying from brown to almost black (Baker et al., 1980a,b). The resin is often moulded into characteristic shapes (Figure 3), indicative of the country of origin (Baker et al., 1980b) such as sticks from India, or rectangular slabs from Morocco with a characteristic imprint (Figure 5).
Variations in the chemical profiles of cannabis products of different origins have been examined, particularly as a means of identifying the source country of seizures; this is reviewed more fully in Chapter 3. Crosby et al. (1984) have suggested that a study of the insects present in a sample of cannabis can allow an exact indication of its country of origin.
The content of the main psychoactive constituent, THC, in cannabis products varies greatly depending on the type of preparation, geographical source, plant strain, quality and age of the preparation. Estimates vary, but according to Fairbairn (1976) marijuana contains up to 8% THC, hashish up to 14% THC, and hash oil up to 60% THC. Sinsemilla buds may contain up to 10% THC (Wills, 1993). In a study comparing THC content of a number of cannabis products confiscated over a ten year period in the United States of America (El Sohly et al., 1984), sinsemilla buds were found to be more potent than the average hashish sample.
The figures given above are approximate upper limits, and values commonly encountered may be considerably lower and occasionally even higher. For example, the average THC content in hash oil samples collected in the American study (El Sohly et al., 1984) was about 18%. A popular cannabis preparation often seized from users is reefers or joints consisting of cigarettes containing marijuana, hashish or hash oil (Wills, 1993). These have been shown to vary greatly (Fairbairn et al., 1974; Humphreys and Joyce, 1982) in the amount of cannabis plant material (11-1090mg) or cannabis resin (6-838 mg) and consequently in the THC content (0.1441 mg) per reefer.
Baker et al. (1980a) have examined the variation in THC content of Cannabis products illicitly imported into the United Kingdom over the period 1975-1978. Geographical variations in potency were seen but these were found to be changeable. For instance, in the early part of the study, herbal cannabis from South East Asia was found to be of a higher quality (i.e. THC content) than from other parts of the world, but its quality had declined by 1978. Jamaican cannabis, however, improved in quality over the same period. Hash oil from India, Kenya and Pakistan had very similar mean THC contents (33, 34 and 30%) in 1977 whereas the values were very different (40, 16 and 18%) in 1978. However, in both this and a further study (Baker et al.,
1982) it was noted that there was considerable variation in THC content even within samples from a given country of origin, and so a single sample could not be considered indicative of the quality of all similar products from that source.
In both the above studies, THC was estimated as the total of THC and delta-9-tetrahydrocannabinolic acid (THCA) since the latter is converted to THC both during the analytical process and during the smoking of cannabis preparations. In a different study however (Baker et al., 1981), the two compounds were estimated individually in a range of marijuana and hashish samples. THC values ranged from 1-10.6% in cannabis herb and 6.0-12.5% in the resin. The THCA: THC ratios in the resins also varied from 0.5:1 to 6.1:1. Higher ratios were encountered in resins from the Mediterranean area, whereas the lower ones were measured in samples from the Indian sub-continent. Thus despite some general trends, there appears to be considerable variation in the THC content of products derived from a single source country both at any given time, and over longer time scales.
The age and storage conditions of cannabis products can affect their potency due to changes in THC content. A 1931 herbal (Grieve, 1974) indicates that two-year old ganja is almost inert. However, according to Fairbairn et al. (1976) the stability of a cannabis preparation depends on its preparation and storage. In one experiment, about 90% of the THC content of marijuana herb was still present after storage for a year at room temperature in the dark (Fairbairn, 1976). Exposure to air and daylight but not air alone had a deleterious effect, particularly on solutions of cannabinoids (Fairbairn et al., 1976). Temperatures of up to 20°C had little effect on stability although higher values caused breakdown of THC. However, another important factor was the integrity of the resin glands (Fairbairn et al., 1976). Damage to these by rubbing or scraping leads to rupture of the glands and exposure of the cannabinoids to oxidation even in the dark. However, the authors concluded that herbal or resin cannabis is reasonably stable for one to two years if stored in the dark at room temperature.
Light alone produces polymerisation of THC whereas oxidation converts THC mainly to CBN, the non-narcotic compound cannabinol (Fairbairn, 1976). Turner et al. (1973) had shown in an earlier study that hexahydrocannabinol and other minor products were produced in addition to CBN. A decomposition pathway of THC to CBN involving a number of hydroxylated intermediates has been suggested by Turner and El Sohly (1979). Harvey et al. (1985) found that in a 140 year old ethanolic cannabis extract, most of the THC had decomposed to CBN and tha
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