Brain Damage

It has long been known that marijuana produces temporary and dose-related alterations in brain waves, but an idea has lingered, probably dating from the anti-marijuana propaganda of the 1930s, that cannabis might cause irreversible brain damage. Two studies have produced disturbing evidence in this regard. The more important research was reported by A. M. C. Campbell and his associates in the December 1971 issue of The Lancet, a British medical journal. The authors claimed that there was evidence of cerebral atrophy (a wasting away of brain tissues) in ten patients who had used cannabis extensively. This observation was the result of a painful and potentially hazardous procedure known as an air encephalogram, and other researchers have been reluctant to repeat it.
    Critics of the experiment point out several problematic facts about the ten subjects. All had used LSD, some fairly often, and eight of the ten had extensive experience with amphetamines. Most of the subjects had used various other drugs as well, including morphine and heroin. At least one of the patients was an epileptic another was mentally retarded, as many as five were thought to be schizophrenic, and several had suffered head injuries from accidents. Moreover, the subjects in this study had been selected because they all showed symptoms of senility, and a few were actually known to have birth defects. In other words, this study was so flawed as to be virtually meaningless.
    The other study that has caused concern was concluded by Dr. Robert Heath at the Tulane University School of Medicine. Heath recorded the brain waves of six rhesus monkeys before, during, and after exposure to marijuana smoke and found that the monkeys showed changes for as long as five days after such exposure. In addition, two of the monkeys suffered "structural alteration of cells in the spetal region of the brain," and Heath stated that previous correlations between monkeys and human beings suggested that the chronic smoking of marijuana produces irreversible damage in humans.
    Heath's report was made public at a Senate subcommittee hearing investigating marijuana and health. Dr. Julius Axelrod, who received the Nobel Prize in 1970 for his work on the effects of drugs on the brain, was asked to evaluate the Heath study. He told the senators that the amount of smoke inhaled by the monkeys was equivalent to a human being smoking over a hundred marijuana cigarettes each day for six months. "The results indicate that marijuana causes an irreversible damage to the brain," said Axelrod. "But the amounts used are so large that one wonders whether it's due to the large toxic amounts Dr. Heath has given." A large enough dose of almost any substance will produce negative results in animals or human beings, said Axelrod, who believed that Heath should have administered doses of varying degrees to determine which effects would have been produced by different levels of marijuana. Lester Grinspoon, another critic of the Heath study, points out that the monkeys in the experiment were forced to ingest excessive amounts of marijuana smoke, although a monkey's lung size is only about one-fifteenth as large as that of a human being.
    At the University of Pennsylvania, a research team headed by Dr. Igor Grant examined twenty-nine marijuana smokers and an equivalent control group, all of them medical students. Grant and his team administered the most sensitive neurological and neuropsychological tests available and found no appreciable differences when they examined the brains of the students in the two groups.