THE BRAIN

Research has not found definitive evidence of long-term permanent brain damage as a result of smoking marijuana. Some research has shown structural brain damage in rodents, but these studies used 100 times the amount of THC that would be a psychoactive dose for humans. In addition, these study results have not been duplicated in primate studies. A study of human marijuana subjects who smoked an average of nine marijuana cigarettes a day found no evidence of brain damage after assessing the brain with CT scans (computed axial tomography, also called CAT scans, in which film images are produced of crosssections of specific tissue). However, many researchers point out that THC changes the ways in which the brain senses and processes information, most notably in the hippocampal region of the brain, and suggest that learning and memory behaviors are affected by marijuana use.

MARIJUANA, MENTAL ILLNESS, AND PSYCHOLOGICAL PROBLEMS

Many researchers have studied the relationship between marijuana and mental illness. Early twentieth century proponents of marijuana prohibition in the United States often cited studies showing a link between marijuana and insanity and referred to reports of large numbers of institutionalized mental patients in India and Egypt who had used marijuana. However, since the 1970s, researchers have effectively refuted the claims of a direct link between marijuana use and mental illness. Although marijuana may not be linked to severe mental illness, research begun in the 1960s has suggested that marijuana can cause subtle psychological damage, particularly to adolescents. Studies have consistently shown that adolescents with psychological and behavioral problems are more likely than other adolescents to use marijuana heavily. Experts and others such as parents, school administrators, and drug abuse counselors often point to marijuana as the primary cause of these problems. They theorize that once marijuana is removed from a troubled adolescent’s life, the troubles will soon depart as well. However, recent research discounts this theory. Most teens who use marijuana heavily are likely to have underlying psychological and behavioral problems. Therefore, heavy marijuana use may add to a teen’s problems, but it is more a symptom than a cause of these problems.