There is no evidence that marijuana use is a cause of brain damage. Studies by Dr. Robert Heath claimed the contrary in experiments on monkeys, but Heath's work has been sharply criticized by the Institute of Medicine and the National Academy of Sciences on three primary counts: (1) its insufficient sample size (only four monkeys), (2) its failure to control experimental bias, and (3) its misidentification of normal monkey brain structure as "damaged" .
A far superior experiment by the National Center for Toxicological Research (NCTR) involving 64 rhesus monkeys that were exposed to daily or weekly doses of marijuana smoke for a year found no evidence of structural or neurochemical changes in the brains of rhesus monkeys. In fact, following the publication of two 1977 JAMA studies, the American Medical Association (AMA) officially announced its support for the decriminalization of marijuana. .
Contrary to a 1987 television commercial sponsored by the Partnership for a Drug-Free America (PDFA), marijuana does not "flatten" brain waves either. In the commercial, a normal human brain wave was compared to what was supposedly the (much flatter) brain wave of a 14-year-old high on marijuana. It was actually the brain wave of a coma patient. PDFA lied about the data, and had to pull the commercial off of the air when researchers complained to the television networks.
In reality, marijuana has the effect of slightly increasing alpha-wave activity. Alpha waves are generally associated with meditative and relaxed states, which are often associated with human creativity.
Marijuana does impair short-term memory, but only during intoxication. Although the authoritative studies on marijuana use seem to agree that there is no residual impairment following intoxication, persistent impairment of short-term memory has been noted in chronic marijuana smokers up to 6 and 12 weeks following abstinence (MacCoun, Rueter, 2001).
