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Twenty-three states plus the District of Columbia have approved pot for medical use. But a new study in the Journal of the American Medical Association is raising questions about its safety and effectiveness. Here's NPR's Patti Neighmond.
PATTI NEIGHMOND, BYLINE: Researchers from the University of Bristol in the United Kingdom reviewed findings from 79 different studies looking at the effect of marijuana on symptoms ranging from chronic pain to sleep difficulties and mental illness. At best, they found only moderate evidence indicating that marijuana reduced nerve pain and pain from cancer. When it came to other conditions, like nausea and vomiting due to chemotherapy, difficulties sleeping or weight loss among HIV patients, there was some anecdotal evidence suggesting that people may be helped by marijuana, but it was just that - anecdote.
DEEPAK CYRIL D'SOUZA: Which is really the bulk of the evidence that the states have used in approving medical marijuana.
NEIGHMOND: In an editorial accompanying this study, Dr. Deepak Cyril D'Souza says states legalizing marijuana for medical use may be jumping the gun before good quality evidence is in.
D'SOUZA: If a pharmaceutical company, for example, wanted to get a drug approved for a medical condition and they only submitted anecdotal data, there's absolutely no chance that that drug would be approved.
NEIGHMOND: D'Souza is a psychiatrist with Yale University's School of Medicine. For years, he's studied the impact of marijuana on mental health. And the big question, he says, is how routine daily use - the way one might use marijuana to treat a medical condition - affects the body and the brain over the long term. Concerns have been raised about memory loss, panic, paranoia and other severe disorders.
D'SOUZA: There is a small risk of schizophrenia or psychotic disorders associated with marijuana use. We don't fully understand why some people appear to be more vulnerable to those effects, but that is a devastating mental disorder for anyone to have.
NEIGHMOND: Some studies suggest cognitive deficits associated with long-term marijuana use. Marijuana's difficult to study because there are hundreds of different components in different strains. But focused study's exactly what's needed, says Dr. D'Souza, who suggests federal and state health officials remove any legal or financial obstacles to getting that done. Patti Neighmond, NPR News. Transcript provided by NPR, Copyright NPR.