History

Dennis J. McKenna, Ph.D. INTRODUCTION

(Ji tlio numerous plant hallucinogens utilized by indigenous populations of the Amazon Basin, perhaps none is as interesting or complex, botanically, chemically, or ethnographically, as the hallucinogenic beverage known variously as ayahuasca, caapi, or yage. The beverage is most widely known as ayahuasca, a Quechua term meaning "vine of the souls," which is applied both to the beverage itself and to one of the source plants used in its preparation, the Malpighiaceous jungle liana, Banisteriopsis caapi (Schultes 1957). In Brazil, transliteration of this Quechua word into Portuguese results in the name, hoasca. Ayahuasca, or hoasca, occupies a central position in mestizo ethnomedicine, and the chemical nature of its active constituents and the manner of its use make its study relevant to contemporary issues in neuropharmacology, neurophysiology, and psychiatry.

WHAT IS AYAHUASCA?

In a traditional context, ayahuasca is a beverage prepared by boiling or soaking the bark and stems of Banisteriopsis caapi together with various admixture plants. The admixture employed most commonly is the

Rubiaceous genus Psychotria, particularly P. viridis. The leaves of P. viridis contain alkaloids that are necessary for the psychoactive effect. Ayahuasca is unique in that its pharmacological activity is dependent on a synergistic interaction between the active alkaloids in the plants. One of the components, the bark of Banisteriopsis caapi, contains 13-carboline alkaloids, which are potent MAO inhibitors; the other components, the leaves of Psychotria viridis or related species, contain the potent short-acting psychoactive agent N,N-dimethyltryptamine (DMT). DMT is not orally active when ingested by itself but can be rendered orally active in the presence of a peripheral MAO inhibitor, and this interaction is the basis of the psychotropic action of ayahuasca (McKenna, Towers, and Abbott 1984). There are also reports (Schultes 1972) that other Psychotria species are similarly utilized in other parts of the Amazon. In the northwest Amazon, particularly in the Colombian Putumayo and Ecuador, the leaves of Diplopterys cabrerana, a jungle liana in the same family as Banisteriopsis, are added to the brew in lieu of the leaves of Psychotria. The alkaloid present in Diplopterys, however, is identical to that in the Psychotria admixtures, and pharmacologically, the effect is similar. In Peru, various admixtures in addition to Psychotria or Diplopterys are frequently added, depending on the magical, medical, or religious purposes for which the drug is being consumed. Although a virtual pharmacopoeia of admixtures are occasionally added, the most commonly employed admixtures (other than Psychotria, which is a constant component of the preparation) are various Solanaceous genera, including tobacco (Nicotiana sp.), Brugmansia sp., and Brunfelsia sp. (Schultes 1972; McKenna et al. 1995). These Solanaceous genera are known to contain alkaloids, such as nicotine, scopalamine, and atropine, which affect both central and peripheral adrenergic and cholinergic neurotransmission. The interactions of such agents with serotonergic agonists and MAO inhibitors are essentially unknown in modern medicine.

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