The hallucinogens consist of natural and synthetic substances that alter perception. Peyote, a natural substance derived from cactus plants, is used in religious rituals by Native Americans in the Southwest. Hallucinogenic properties are found in several other natural substances including some fungi, mushrooms, and seeds. Ergot alkaloids, commonly found in moldy rye bread, have hallucinogenic properties, and may have accounted for the bizarre behaviors of the women involved in the Salem witch trials.

Marijuana
Like the opiates, cocaine, and alcohol, marijuana has been around for thousands of years. The first recorded description of the intoxicating effects of marijuana is found in ancient Chinese accounts of its medical use, more than four thousand years ago.

The active ingredients of marijuana are found in the resins of the hemp plant, Cannabis sativa. This leafy plant grows wild in most warm climates and was cultivated in colonial America to make ropes and fishing nets from the fibrous portion of the stems. The leaves of the marijuana plant can be dried and smoked for an intoxicating effect, and the resin can be extracted and concentrated into other forms such as hash oil.

The question of whether marijuana is dangerous as an addictive drug is highly controversial and politicized. Marijuana was listed in the U.S. Pharmacopoeia as late as the 1940s as a remedy for cough, migraines, menstrual cramps, and other conditions. Extracts of the active marijuana resin were available as over-the-counter tonics in the nineteenth and early twentieth centuries.

In 1937 the Marihuana Tax Act [sic] was enacted at the federal level. Most states had already passed laws regulating the sale and use of marijuana. This was the era of alcohol prohibition, and the recreational use of marijuana had come to replace alcohol in some social circles. A propaganda campaign was launched, designed to heighten public fears about marijuana. By the late fifties and early sixties, this had backfired.

Marijuana had been touted to cause insanity, violence, debauchery, and other evils. Recreational users, on the other hand, experienced mild intoxication with very few adverse effects. Marijuana came to be widely used on college campuses and by those in the hippie movement, and eventually spread to other levels of society. Laws were passed to decriminalize the possession and use of marijuana, but it remains classified by the Drug Enforcement Administration as a Schedule 1 drug, along with drugs such as heroin and LSD, which are felt to be dangerous and without legitimate medical use. Stiff penalties remain in effect for the manufacture and sale of marijuana.

In the eighties and nineties, the use of marijuana for certain medical conditions began to attract widespread interest.

Marijuana is known to reduce the pressure in the eye that causes glaucoma. It also stimulates appetite and helps counteract the violent nausea associated with cancer chemotherapy.

It has been used in pain management and as a muscle relaxer or tranquilizer. Researchers have studied it extensively and have developed some pharmaceutical preparations, such as Marinol, which is used for its antinausea and appetite-stimulating properties. Making marijuana readily available for medical use remains highly controversial and problematic.

Our familiarity with what marijuana actually does in the brain is fairly limited compared with how much we know about other drugs like opiates or alcohol. Part of the problem lies in the fact that natural cannabis contains many different compounds, most of which are active in one way or another.

It is generally agreed that the major active component of marijuana is a chemical known as delta-9 tetrahydrocannabinol, or THC. Those who use natural marijuana for various medical reasons contend, however, that THC alone does not have the same beneficial effect as the natural substance.