And this claim is the basis for the lies that make this claim - even the BBC still has a reefer madness post about this "on this day" in 1974.
In 1974, Dr. Robert G. Heath, a researcher at Tulane University in New Orleans, reported that he had found proof that marijuana caused brain damage while experimenting on monkeys. Heath reported that rhesus monkeys smoking an equivalent of 30 joints a day began to atrophy and die after just 90 days. Autopsies revealed that the monkeys who had been exposed to the marijuana smoke had more dead brain cells than the control monkeys, who had not been exposed.
How did Heath come up with these results? What were his procedures? For six years, no one knew. It took Playboy and NORML six years of requesting and suing under the Freedom of Information Act to finally receive an accurate accounting of the procedures Heath used.
Four monkeys were strapped into chairs with transparent plastic boxes surrounding their heads. The head chamber was sealed so that the smoke being pumped in wouldn't be lost. This also meant that the carbon monoxide couldn't escape either. Instead of the 30-joints-a-day dosage that Heath had reported, the monkeys were given the equivalent of 63 joints in five minutes, every day, for three months.
The poor monkeys were being suffocated for five minutes at a time, on a daily basis, over a period of three months. After which they were killed so that their brains could be autopsied, and the dead brain cells caused by carbon monoxide poisoning were attributed to marijuana. This was Ronald Reagan's "reliable scientific" source.
here's a link to the original research report -
http://www.wireheading.com/intracran/cannabis.html
This study was reviewed by a distinguished panel of scientists sponsored by the Institute of Medicine and the National Academy of Sciences. Their results were published under the title, Cannabis and Health in 1982. Heath's work was sharply criticized for its insufficient sample size (only four monkeys), its failure to control experimental bias, and the misidentification of normal monkey brain structure as "damaged". Actual studies of human populations of cannabis users have shown no evidence of brain damage. For example, two studies from 1977, published in the Journal of the American Medical Association (JAMA) showed no evidence of brain damage in heavy users of cannabis. That same year, the American Medical Association (AMA) officially came out in favor of decriminalizing cannabis. That's not the sort of thing you'd expect if the AMA thought cannabis damaged the brain.
http://www.erowid.org/plants/cannabis/cannabis_info14.shtml
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