USA Availability: Illegal to possess except in hydrochloride form, which is prescription
Uses. This pain-relieving drug is derived from thebaine. In jurisdictions where etorphine is legal, it is used as a veterinary sedative. The substance is powerful. Depending on dosage method and animal species receiving the drug, its strength is estimated as anywhere from 10 times to 80,000 times that of morphine, so a person administering the drug must be skilled in order to avoid a serious overdose. The related Schedule II controlled substance dihy-droetorphine is also powerful—10 to 10,000 times stronger than morphine. Etorphine acts quickly. Veterinarians and naturalists use etorphine darts to knock down wild elephants and grizzly bears. Zoos utilize the drug on white rhinoceros, giraffes, and other animals when medical necessity requires them to be unconscious.
Human tests show that etorphine can relieve intense pain without causing unconsciousness. Tests using dihydroetorphine alone and in combination with acupuncture have found the drug to be safe and effective for easing labor pain in childbirth. The substance has relieved pain in cancer patients. Experimenters suspect that as well as being a more powerful pain reliever than morphine, dihydroetorphine may also be less likely to create dependence in a patient.
Opiates and other depressants normally interfere with physical performance. Administered in a particular way, however, etorphine reliably produces a "paradoxical" effect (opposite to an expected effect) of increasing athletic performance by stimulating physical activity while reducing pain. Racehorses have been doped with the drug to make them run faster. Many lovers of the sport disapprove of the practice not only for its illegality but because the horse is harmed. Perhaps the most notorious incident occurred in the late 1980s when Rocket Racer won the Perth Cup by eight lengths and continued running. The horse would not stop despite the jockey's efforts; after nearly another lap around the track, the horse collapsed and died. Reportedly some human track competitors have used the same drug, accelerated their pace as a race progressed, and had difficulty stopping after crossing the finish line.
Drawbacks. In animal experiments dihydroetorphine interferes with the immune system, interference that may make infections more likely. Etorphine can send blood pressure up or down, reduce body temperature, and impair heartbeat and breathing. Impaired breathing is also an unwanted effect observed with dihydroetorphine, along with constipation, nausea, vomiting, dizziness, and drowsiness.
Although etorphine is a standard veterinary medicine, knowledgeable users treat it with great respect and keep an antidote on hand because accidental injection can be fatal. The drug may be absorbed though the skin, and supplies of etorphine are generally dyed red so users can readily tell if they have touched it (such as a smear across a shirt or hand). Swift administration of an antidote can prevent death.
The quantity needed to kill a person is so minute that its presence in a body can be difficult or even impossible to detect. Harmless chemicals added to a dose can make etorphine even harder to discover through laboratory tests. The drug has also attracted military attention as a possible chemical warfare agent.
Abuse factors. When humans in an experiment received etorphine they experienced euphoria and described the drug as feeling like morphine. Researchers who administered etorphine in that experiment concluded that the drug is likely to be abused. Misuse has been noted in China. Other investigators reached the same conclusion about dihydroetorphine from the way rats responded to it. The U.S. Drug Enforcement Administration has ruled that dihy-droetorphine's abuse potential is similar to heroin's. The government of Hong Kong has noted dihydroetorphine's lower price and less stringent control make it appealing to heroin addicts. Lawsuits against the tobacco industry unearthed documentation indicating one company considered the possibility that competitors might lace cigarettes with etorphine to add an addictive need that could not be satisfied by other brands, thereby coercing consumer loyalty to a particular product.
A mice study found no dependence at all after dihydroetorphine had been administered for six days, but rat and mice research demonstrates that dihy-droetorphine eventually produces enough dependence to cause withdrawal symptoms. Investigators have noted that rats act as if dihydroetorphine is a satisfactory substitute for heroin. Etorphine can prevent withdrawal symptoms in morphine addicts, an action demonstrating cross-tolerance between the two drugs, but an etorphine dose holds off withdrawal symptoms for a shorter time than morphine would. In rhesus monkey experiments etorphine and dihydroetorphine are both cross-tolerant with morphine. In those same experiments, when dihydroetorphine dosage was suddenly stopped, few withdrawal signs appeared. Withdrawal symptom research on mice indicates that dihydroetorphine may do more than substitute for morphine: A dihy-
droetorphine dose may actually make morphine withdrawal symptoms go away, so further doses of either drug become unnecessary. Such a result would be inconsistent with what is known about opiate dependence, but discovery of new facts can change scientific understandings. Some researchers believe that etorphine and dihydroetorphine have potential for treating opiate addiction. Dihydroetorphine has been used for that purpose in China but seems to produce even stronger dependence among heroin addicts than methadone. So perhaps animal experiment findings that indicate low dependence potential in dihydroetorphine cannot be extrapolated to humans.
Drug interactions. Giving etorphine and morphine together increases pain relief in mice, while the etorphine does not seem to increase the strength of opiate dependence in the combination. Researchers speculate that the improved pain control might be great enough to allow much smaller doses of morphine in humans than would otherwise be needed, which in turn would greatly decrease the amount of dependence otherwise created by normal-size morphine doses.
Cancer. Not enough scientific information to report. Pregnancy. Not enough scientific information to report. Additional scientific information may be found in:
Firn, S. "Accidental Poisoning by an Animal Immobilizing Agent." Lancet 2 (1973): 95-96.
"Immobilon: Curiously Strong." Lancet 2 (1977): 178.
Jasinski, D.R., J.D. Griffith, and C.B. Carr. "Etorphine in Man. 1. Subjective Effects and Suppression of Morphine Abstinence." Clinical Pharmacology and Therapeutics 17 (1975): 267-72.
Marcoux, G.S. "Etorphine: A New Opiate of Abuse?" Canadian Journal of Psychiatry 41 (1996): 261.
"Schedule II Control of Dihydroetorphine under the Controlled Substances Act (CSA)." Federal Register 65 (2000): 69442-43.
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