Marijuana, common name for a drug made from the dried leaves and flowering tops of the Indian hemp plant Cannabis sativa. People smoke, chew, or eat marijuana for its hallucinogenic and intoxicating effects. It is known by a number of slang names, including “pot,” “grass,” “reefer,” “weed,” and “Mary Jane.”

The flowering tops of the Cannabis plant secrete a sticky resin that contains the active ingredient of marijuana, known as delta-9-tetrahydrocannabinol (THC). The plant has both male and female forms, and the sticky flowers of the female plant are the most potent. Hashish is a similar drug prepared from the same plant. It differs from marijuana in that it is comprised of only the resin from the plant, whereas marijuana is made up of flowering tops and leaves.

Known in India, Central Asia, and China as early as 3000 BC, marijuana has long been used as both a medicine and an intoxicant. It gained widespread use in the United States in the 1960s and 1970s, becoming the second most popular drug after alcohol, and its popularity continued through the end of the 20th century, particularly among American teens. According to a survey prepared in 1998 by the United States Drug Enforcement Agency, marijuana use among teenagers increased almost 300 percent from 1992 to 1998.

Most countries consider marijuana an illegal substance, but individual countries vary on how they prosecute the use and possession of marijuana. Some countries only impose small fines, while others impose harsher punishment, including imprisonment.

The Institute of Medicine of the National Academy of Sciences conducted a 15-month study of the health-related effects of marijuana in 1982. They appointed a 22-member committee to analyze existing scientific evidence bearing on the possible hazards to the health and safety of users of marijuana. The report concludes: "the scientific evidence published to date indicates that marijuana has a broad range of psychological and biological effects, some of which, at least under certain circumstances, are harmful to human health". In a companion report providing policy recommendations to the Academy's National Research Council, regulation of the marijuana market is advocated as the most effective method of controlling marijuana. The National Academy of Science's report rebuts many of the exaggerated claims made about marijuana.

1. Of the 421 chemicals in marijuana, only 61 are unique to marijuana. The chemicals are known as cannabinoids. One of them, delta-9 THC, produces the psychoactive effect and is the focus of most research. The other 360 chemicals in the marijuana plant are found throughout other natural substances.2. The higher potency marijuana grown in the United States represents about half of all the marijuana consumed here. Because of it's higher potency many smokers use far less of it than less potent marijuana.

3. Differences in dosage and frequency of consumption render comparisons between marijuana and tobacco consumption invalid, despite similarity in the composition of their smoke. Marijuana smoke irritates the lungs. Heavy exposure of the lungs to irritation such as smoke increases the likelihood of lung cancer and other lung problems. Marijuana speeds the heartbeat and is unhealthy for people with high blood pressure or other cardiovascular ailments.

4. Marijuana does reduce the sperm count and obstruct sperm mobility in males within the normal range. These side-effects do not seem to affect human fertility, and are completely reversible thirty days after cessation of use. Marijuana, like other drugs, crosses the placenta. While the effects of this are unknown and there is no evidence that marijuana causes chromosome damage, we advise women to avoid the use of marijuana, tobacco, alcohol, or other drugs not prescribed by their physician during pregnancy and nursing.

5. The intoxicating chemical, THC, is broken down by the human metabolism after two or three hours in the body. The by-products of this chemical breakdown are referred to as metabolites. These metabolites are fat soluble, and take 21-30 days to leave the human body via the urine. These metabolites exert no psychoactive effect on the human body.

6. After reviewing all of the evidence, the Academy concluded: "There is not yet any conclusive evidence as to whether prolonged use of marijuana causes permanent changes in the nervous system or sustained impairment of brain function and behavior in human beings". "Interpretation of the evidence linking marijuana to 'amotivational syndrome' is difficult. Such symptoms have been known to occur in the absence of marijuana. Even if there is an association between this syndrome and the use of marijuana, that does not prove that marijuana causes the syndrome. Many troubled individuals seek an 'escape' into use of drugs: thus frequent use of marijuana may become one more in a series of conterproductive behaviors for these unhappy people".

7. "Cannabis and it's derivatives have shown promise in the treatment of a variety of disorders. The evidence is most impressive in glaucoma, where their mechanism of action appears to be different from standard drugs: in asthma.... and in the nausea and vomiting of cancer chemotherapy... Similar trials have suggested cannabis might also be used in seizures, spasticity, and other nervous system disorders".
(related; Cannabis Sativa, Cannabis Indica,)