September 16, 2011

Marijuana or hemp (Cannabis sativa) is a plant that has been cultivated for thousands of years in various parts of the world for its fiber, seeds, medicinal, and psychoactive properties. The chemical compounds responsible for the intoxicating and therapeutic effects are found in the sticky resin released from the flowers of female plants. The marijuana plant contains more than 400 known compounds of which about 60 have a structure similar to cannabinoids. The main psychoactive substance is generally believed to be delta-9tetrahydrocannabinol (THC). Cannabinoids act on a specific receptor that is widely distributed in the brain regions involved in cognition, memory, pain perception, and motor coordination.

Marijuana (“grass,” “weed,” “pot”) is prepared by drying the leaves and the flowering tops of the plant, and may be smoked in a rolled cigarette (“joint”), in a pipe, or, more recently, in a cigar (“blunt”). Hashish consists of dried cannabis resin and generally contains higher levels of THC. Cannabis preparations may also be eaten or drunk as a tea, but smoking is the easiest way to achieve the desired psychoactive effects.

In the United States and most of the developed world, cannabis is an illegal substance and is primarily used for its psychoactive properties. However, for centuries marijuana has been used in various parts of the world not only as an intoxicating agent but also as a medicinal substance.

From 1850 until 1937, cannabis was used in American medical practice for a wide range of conditions. The Marijuana Tax Act of 1937 introduced the first federal restrictions on marijuana and outlawed the nonmedicinal, untaxed possession or sale of the drug. The Comprehensive Drug Abuse Prevention and Control Act of 1970 classified marijuana as a Schedule I controlled substance. Since then, there have been several attempts to legalize its medical use. In 1987, the Food and Drug Administration approved dronabinol, a compound containing synthetic THC, as a Schedule II controlled substance for treatment of chemotherapy-induced nausea and vomiting.

In the United States, cannabis became a major drug of abuse in the late 1960s, with peak usage occurring in the late 1970s and early 1980s. According to the Monitoring the Future Survey, in 1979, about 51% of high school seniors reported having used marijuana at least once in the past 12 months. The lowest levels of use occurred in 1992 with about 22% reporting annual use. The 1990s saw the resurgence of use, and annual prevalence rates peaked in 1997 reaching almost 40% among twelfth-grade students. Currently, marijuana is the most commonly used illicit drug in the United States according to the 2001 edition of the National Household Survey on Drug Abuse.

Despite the fact that cannabis is one of the most widely used psychoactive substances in the world, its health and psychological effects are still not well understood and remain the subject of much debate. Due to its legal status, clinical studies of marijuana are difficult to conduct. As a result, data on the adverse effects of the drug are more extensive than data on its therapeutic effectiveness.

Cannabinoids produce a variety of acute psychological effects in humans. THC is rapidly absorbed into the bloodstream after smoking, and acute peak effects appear between 10 and 60 min, diminishing substantially over the next 2-4 hr. Oral administration is slower to take effect and lasts longer. Psychological effects (being “high” or “stoned”) are usually characterized by euphoria and relaxation coupled with the intensification of ordinary sensory experiences, including sexual activity. Shortterm memory and attention, motor skills, and reaction time are also impaired while a person is intoxicated. High doses of the drug can facilitate anxiety, paranoia, and panic in both experienced and naive users.

For a long time it was thought that marijuana dependence was not possible. Recent research suggests tolerance and withdrawal, and therefore dependence, may occur in long-term, high-dose (daily) users; however, it is not seen in casual or moderate users. The symptoms of withdrawal may include irritability, insomnia, restlessness, loss of appetite, and more, but none are life threatening.

Physiological effects are many and varied but particularly noteworthy for individuals with cardiovascular problems, since the fluctuations in blood pressure and increases in heart rate exacerbate those problems. There are no reports of deaths that are directly linked to cannabis overdose from its acute effects in healthy adults. A number of in vitro and in vivo studies suggested that the immune system may be impaired after exposure to cannabis. However, the clinical significance of these changes is not well understood, and there is no conclusive evidence that consumption of cannabis impairs human immune function. Studies conducted with HIVpositive homosexual men have shown that cannabis use was not associated with an increased risk of development of AIDS among HIV-infected individuals.

Although there is a paucity of information on gender-specific marijuana effects, some evidence suggests that cannabis affects sex hormones. In animal studies, chronic administration of high doses of THC lowers testosterone secretion, impairs sperm production in males, and disrupts the ovulation cycle in females. However, evidence of the effects of cannabis on human fertility is inconclusive. Suffice it to say, individuals experiencing fertility problems would benefit from remaining abstinent from cannabis.

In some parts of the world, cannabis preparations were thought to have therapeutic value in childbirth and pregnancy. In modern medical practice, cannabis is considered to have damaging effects on the fetus. Numerous studies have explored cannabis as a perinatal risk factor, but the results of these studies have been contradictory, and it was difficult to isolate the effects of cannabis from many other variables that could influence the outcomes of pregnancy. Nevertheless, new clinical studies suggest that prenatal exposure to cannabinoids does result in adverse consequences for the offspring. However, these defects are subtle and are not apparent immediately after birth. Again, for pregnant or breast-feeding women, abstinence from cannabis should be the norm.

Advocates of the medical marijuana movement argue that cannabis has numerous therapeutic properties and is less toxic and more effective than some conventional therapies. Considerable debate exists in this area and will not be resolved soon, in large part because there is a lack of clinical studies to evaluate potential benefits and adverse effects in comparison to other existing therapies.

SEE ALSO: Addiction, Substance use

Suggested Reading

  • Adams, I. B., & Martin, B. R. (1996). Cannabis: Pharmacology and toxicology in animals and humans. Addiction, 91, 1585—1614.
  • Grinspoon, L., & Bakalar, J. (1997). Marijuana, the forbidden medicine. New Haven, CT: Yale University Press.
  • Hollister, L. E. (1998). Health aspects of cannabis: Revisited. International Journal of Neuropsychopharmacology, 1, 71—90.
  • Joy, J. E., Watson, S. J., & Benson, J. A. (Eds.). (1999). Marijuana and medicine: Assessing the science base. Washington, DC: National Academy Press.
  • Mathre, M. L. (Ed.). (1997). Cannabis in medical practice: A legal, historical and pharmacological overview of the therapeutic use of marijuana. Jefferson, NC: McFarland.
  • Onaivi, E. S. (Ed.). (2002). Biology of marijuana: From gene to behavior. London: Taylor & Francis.


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