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Module 4
Weeding Out the Grass
Background
MARIJUANA
Marijuana comes from the dried leaves and flowers of the cannabis plant. It can be smoked, cooked into baked goods, or brewed into tea. It contains more than 400 chemicals. Smoking marijuana, like smoking tobacco, can have negative effects on the lungs, even causing lung cancer.
Marijuana also has potentially dangerous short-term effects that can last more than 4 hours. In low to medium doses, marijuana can cause relaxation, reduced coordination, reduced blood pressure, sleepiness, attention problems, and an altered sense of time and space. In high doses, marijuana can cause hallucinations, delusions, memory problems, and disorientation.
Slang terms for marijuana include pot, herb, weed, grass, chronic, ganja, and hash.
Marijuana and Neurotransmitters
Tetrahydrocannabinol (THC) is the active ingredient in marijuana that causes changes in the brain. THC activates specific receptors, known as cannabinoid receptors, which are located in the limbic system, cerebral cortex, and cerebellum. In student materials, cannabinoid receptors are referred to more simply as THC receptors. Because these receptors are located in many areas of the brain, the effects are widespread. In the healthy brain, cannabinoid receptors are activated by a neurotransmitter called anandamide. Anandamide is known to have a pain-relieving effect and may also play a role in numerous other brain activities. THC has many of the same effects as anandamide and can bind to the same receptors. But when THC activates the receptors, it interferes with the normal functioning of these areas of the brain.
Since the discovery of anandamide, scientists have discovered other similar neurotransmitters that also act on the receptor where THC binds. They are still investigating the function of both anandamide and these other neurotransmitters.
Marijuana also affects the neurotransmitter dopamine, which is responsible for feelings of pleasure and euphoria. This is the same neurotransmitter that is affected by alcohol, nicotine, heroin, and cocaine. Long-term use of marijuana can change the balance of these neurotransmitters.
Effects of Marijuana
While someone is using marijuana, activity in the hippocampus is reduced, causing problems with short-term memory. Animal studies of long-term marijuana use have shown damage in this area. Research with people has found that chronic use of marijuana can cause permanent memory and cognitive problems, especially at young ages. Specifically, one study found that young people who used marijuana before the age of 17 had significantly lower verbal IQs, or the ability to think with words and process verbal information, than both people who began using the drug at an older age and people who never used it at all. These studies show that marijuana can be particularly harmful when it is used by young people when the brain is still developing.
Short-term effects of marijuana use include distorted perception, due to the drug’s interference with the brain’s ability to process sensory information. Information about touch, sight, sounds, and time are distorted because of marijuana’s effects on the cerebral cortex. Short term
marijuana use can also interfere with the normal functioning of the cerebellum. This can cause
problems with balance, posture, and the coordination of movement.
Long-term use of the drug can also lead to a series of attitude and personality changes, known as “amotivational syndrome.” This syndrome is characterized by a diminished ability to carry out
long-term plans, a sense of apathy, decreased attention to appearance and behavior, and decreased ability to concentrate for long periods of time. These changes can also include poor performance in school.
Marijuana Withdrawal
New research is showing that long-term marijuana use may lead to addiction. When the drug is no longer available, the user may develop an uncontrollable desire for the drug and withdrawal symptoms including decreased appetite, weight loss, disruption in sleep, increased irritability, restlessness, and anger.
Medical Uses of THC
There are some medicines that contain THC. They are used for treating nausea and vomiting associated with chemotherapy for cancer treatment, and for improving appetite which is one of the complications of AIDS.
Although THC can be very helpful to people suffering from cancer, and AIDS, it continues to have negative side effects. Scientists are studying the drug so that they can develop a therapeutic drug that is free of THC’s negative consequences. Another chemical related to THC, nabilone, has been approved by the U.S. Food and Drug Administration for treating nausea associated with cancer treatment. Research in this important area continues.
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Contact Information
For questions regarding NIDA's Science Education Program and Materials, contact Cathrine Sasek, Ph.D., e-mail: csasek@nih.gov.
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