Hallucinogens and Psychedelics

Hallucinogens and psychedelics do not share a common mechanism of action, but all induce hallucinations. These drugs can either be natural such as mescaline, which is derived from the peyote cactus, or synthetic such as lysergic acid diethylamide (LSD), but they are typically classified pharmacologically according to the affected neurotransmitter system.

Cholinergic psychodelics (drugs altering acetylcholine transmission) include physostigmine, scopolamine, and atropine. Drugs that alter norepinephrine transmission include mescaline and ecstasy. Drugs that alter serotonin transmission include LSD and psilocin. Other drugs in this category include the psychedelic anesthetics phencyclidine (PCP) and ketamine.

Marijuana, which is derived from the hemp plant Cannabis sativa, is often classified as a psychedelic substance, although only in very high doses does it produce sensory distortions. Marijuana's most common behavioral symptom is sedation. Unlike other drug classes, and with the exception of the cholinergic psychedelics, hallucinogenic and psychedelic drugs are generally nonlethal even when taken in large doses.

Other Drugs that Affect the Central Nervous System

Additionally, there are a number of other drugs that affect central nervous system functioning. These compounds are used to treat a variety of psychological and neurological disorders and include antidepressants, antipsychotic medication, and drugs for epilepsy, Parkinson's disease, the dementias (such as Alzheimer Disease), and spasticity.

Categorizing Drugs into Five Schedules

A different approach to the classification of psychoactive drugs is taken by the legal system, which considers all illegal drugs or controlled substances "narcotics." According to the Comprehensive Drug Abuse Prevention and Control Act of 1970, drugs are categorized into five schedules according to the perceived risk of dependency.

Schedule I drugs, such as heroin, marijuana, and most psychedelics, have a high risk of dependency and no widely accepted medical use. These drugs are forbidden and cannot be obtained even by prescription (although marijuana is available in some states). Schedule II drugs, such as morphine, codeine, amphetamines, and certain barbiturates, have a high risk of dependency but are accepted by the medical community for treatment. Schedule III drugs have a risk of moderate physical dependency or high risk of psychological dependency and include preparations with limited opiates (morphine) and barbiturates not in Schedule II.

Schedule IV drugs, which include the benzodiazepines, have a slight risk of mild physical or psychological dependency. Schedule V drugs have less risk of mild physical or psychological dependency. Finally, alcohol and tobacco are not classified under this law. They fall under the jurisdiction of the Bureau of Alcohol, Tobacco and Firearms (ATF), which is a division of the U.S. Department of the Treasury.

SEE ALSO Alcohol AND Health; Drug Testing; Nervous Systems; Neuron; Synaptic Transmission

Arne Dietrich

Bibliography

Goodman, Louis S., et al., eds. Goodman & Gilman's The Pharmacological Basis of Therapeutics, 9th ed. Elmsford, NY: McGraw-Hill, 2000.

Ross, R. T. How to Examine the Nervous System, 2nd ed. Stamford, CT: Appleton & Lange, 1999.

Schatzberg, Alan F., and Charles B. Nemeroff, eds. Textbook of Pharmacology, 2nd ed. Washington, DC: American Psychiatric Press, 1995.

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