This section deals with a collection of drugs that do not fit easily under other topic headings in this chapter or the chapter on CNS depressants (Chapter 12). All of the drugs are drugs of abuse and could be organized under that heading.
The jS-arylamino hallucinogens arose because of interest in the naturally occurring hallucinogens psilocin and mescaline and in modifying the amphetamines, which were popular drugs at the time. Lysergic acid diethylamide (LSD) was accidentally discovered during research on ergot alkaloids. It is of scientific interest because it serves as one model for clinical psychosis. Phencyclidine (PCP) is scientifically interesting because it gives information about the ionotropic N-methyl-d-aspartate glutamic acid receptor, and its CNS effects serve as a model for schizophrenia.
Cocaine as a CNS stimulant is a pernicious drug of abuse. Research on why it is so strongly addictive and on drug measures that might mitigate its effects has been intense in the past 2 decades.
A ^Tetrahydrocannabinol and its relatives were studied for many years to determine the SARs. The field was given stimulus with the discovery of the endogenous cannabinoid receptors. Presently, the endogenous cannabinoid system is under investigation.
A property of the 1^-arylamino hallucinogens is alteration of the perception of stimuli. Reality is distorted, and the user may undergo depersonalization. Literally, the effects are those of a psychosis. Additionally, the drugs can produce anxiety, fear, panic, frank hallucinations, and additional symptoms that may be found in a psychosis. Accordingly, they are classed as hallucinogens and psychotomimetics.
This group can be subgrouped into those that possess an indolethylamine moiety, those that possess a phenylethyl-amine moiety, and those with both. In the first group, there is a structural resemblance to the central neurotransmitter 5-HT, and in the second, there is a structural resemblance to NE and DA. This resemblance is suggestive, and there may be some selectivity of effects on the respective transmitter systems. With structures of the complexity found in many of these agents, however, a given structure may possibly affect not just the closest structurally related neurotransmitter systems but other systems as well. Thus, a phenethylamine system could affect not only NE and DA systems but also 5-HT systems, and an indolethy-lamine system could affect not only 5-HT but also NE and DA systems.
Dimethyltryptamine is a very weak hallucinogen, active only by inhalation or injection, with a short duration of action. It possesses pronounced sympathomimetic (NE) side effects.
Psilocybin and Psilocin
Psilocybin is the phosphoric acid ester of psilocin and appears to be converted to psilocin as the active species in vivo. It occurs in a mushroom, Psilocybe mexicana. Both drugs are active orally, with a short duration of action.
Synthetic a--methyl-substituted relatives have a much longer duration of action and enhanced oral potency.35 This suggests that psilocin is metabolized by MAOs.
Mescaline, 3,4,5-trimethoxyphenethylamine, is a much-studied hallucinogen with many complex effects on the CNS. It occurs in the peyote cactus. The oral dose required for its hallucinogenic effects is very high, as much as 500 mg of the sulfate salt. The low oral potency probably results from facile metabolism by MAO. a-Methylation increases CNS activity. Synthetic a-methyl-substituted relatives are more potent.35,36 The drugs 2,5-dimethoxy-4-methylamphetamine (DOM), 3,4-methylenedioxyamphetamine (MDA), and 2,5-dimethyl-dicyanoquinonediimine (DMDA; ecstasy) are extremely potent and are dangerous drugs of abuse.
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