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I INTRODUCTION

Marijuana, common name for a drug made from the dried leaves and flowering tops of the Indian hemp plant Cannabis sativa (see Cannabis). 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.”
Marijuana Plant Marijuana is formed from the dried leaves and flowering tops of the Indian hemp plant Cannabis sativa. Popularly known as “grass,” “pot,” “reefer,” and “Mary Jane,” marijuana is smoked or chewed for its intoxicating effect, and it has also been used as a sedative and analgesic. Hashish is formed from the resin of the flowering tops of the same plant, and it is five to eight times more potent than marijuana when smoked.Photo Researchers, Inc.
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.

II EFFECTS

Many users describe two phases of marijuana intoxication: initial stimulation, which includes giddiness and euphoria, followed by sedation and pleasant tranquility. Mood changes are often accompanied by altered perceptions of time and space. Thinking processes become disrupted by fragmentary ideas and memories. Many users report increased appetite, heightened sensory awareness, and general feelings of pleasure.
Negative effects of marijuana use can include confusion, acute panic reactions, anxiety attacks, fear, a sense of helplessness, and loss of self-control. Chronic marijuana users may develop amotivational syndrome characterized by passivity, decreased motivation, and preoccupation with taking drugs. Like alcohol intoxication, marijuana intoxication impairs judgment, comprehension, memory, speech, problem-solving ability, reaction time, and driving skills.
The effects of long-term marijuana use on the intellect have not been established, and there is no evidence that marijuana causes brain damage. Smoking marijuana can damage the lungs, however, and long-term use may increase the risk of lung cancer. Although marijuana is not physically addicting and no physical withdrawal symptoms occur when use is discontinued, psychological dependence develops in some 10 to 20 percent of long-term regular users (see Drug Dependence).

III MEDICAL USES

Some people find that marijuana combats the unpleasant symptoms associated with medical conditions. But the potential medical uses of marijuana are hard to assess, as there have been few clinical trials. Pure THC has been shown to improve appetite and prevent the severe weight loss associated with acquired immunodeficiency syndrome (AIDS), and it also reduces the nausea caused by cancer chemotherapy and radiation treatments. Pure THC sold under the brand name Marinol is available in capsule form as a prescription medicine in the United States for these uses. Compared to smoked marijuana, however, this drug is slower to provide symptom relief due to the time required for the drug to be absorbed into the bloodstream. Marijuana is also reported to have beneficial effects in treating pain and muscle spasms in patients with multiple sclerosis (MS). Many people who suffer from MS and other chronic diseases report that marijuana provides symptom relief when all other medications fail.
In the United States, the potential medical benefits of marijuana have sparked a debate about the legalization of marijuana for medicinal purposes. Since 1986 nine states—Alaska, Arizona, California, Colorado, Hawaii, Maine, Nevada, Oregon, and Washington—have passed legislation that permits patients to possess and grow marijuana for medicinal purposes with their doctor’s approval. These state laws are not in accordance with federal laws, which prohibit the use, possession, growth, or distribution of marijuana for any purpose. In 2001 the U.S. Supreme Court ruled in United States v. Oakland Cannabis Buyers' Cooperative that marijuana distributors cannot offer a medical-necessity defense to avoid a federal conviction for marijuana manufacture, distribution, and possession. Some proponents of medical marijuana fear that this ruling may eventually make it more difficult for individuals to claim a medical-necessity defense in state courts. In the United Kingdom large-scale clinical trials of cannabis-based medicines for pain and multiple sclerosis were initiated in 2000. If successful these trials could lead to the approval of such medicines in Europe.