Estudios sobre beneficios de la marihuana no son concluyentes

By Liz Szabo, USA TODAY
Advocates of medical marijuana tout its ability to alleviate the symptoms of a number of diseases, from multiple sclerosis, glaucoma, epilepsy and AIDS to nausea caused by chemotherapy. While experts say marijuana may be promising, they note that there hasn’t been enough solid research to prove these claims.
«The evidence is just not there,» says Stanley Watson, a University of Michigan professor of psychiatry and one of two principal authors of a 1999 report by the Institute of Medicine (IOM), a private, non-profit organization that advises the government on health policy. «The studies that have been done have just not been well-enough designed.»
Organizing a study of the health benefits of an illegal drug is a challenge, says John Benson, the other principal author of the IOM report, which called for more research into marijuana’s possible medical benefits. The American Medical Association in 2001 issued a statement that seconded that call.
Marijuana’s potential benefits are limited by the harm caused by smoking, which can increase the risk of cancer, damage the lungs and cause pregnancy complications, such as low birth weight, states the IOM report.
The IOM report found no conclusive data to support the idea that pot causes people to take up harder drugs, or that approving it for medical use would increase its use among the public.
Yet marijuana’s medical benefits are often modest, Watson says. Almost all breast cancer patients treated with a chemotherapy drug called cisplatin become nauseated. Standard drugs can reduce that rate to 10%, while marijuana lowers the number to only 25%. «If you have a family member with this illness, what would you put them on?» Watson asks.
The Food and Drug Administration has approved a drug called Marinol — a form of THC, an active ingredient in marijuana — to treat AIDS-related weight loss as well as chemo-induced nausea. Benson says the drug, which often produces a hangover, is not very popular.
Scientists have studied marijuana’s effects on several ailments:
•AIDS. Research shows that marijuana stimulates the appetite among AIDS patients, who often waste away. «Patients gained a little weight, and they ate a lot of junk food,» says Benson, who notes that sweets and snacks don’t improve nutrition.
•Glaucoma. Smoking marijuana should not be used to treat glaucoma, according to the IOM report. Although it relieved eye pressure, those effects were short-lived.
•Epilepsy and multiple sclerosis. There is «limited scientific evidence» that marijuana produces any measurable medical benefits, according to an article last year in Neurology.
The drug remains popular with some patients, however. In two Canadian studies also published in Neurology, one found that 36% of 220 MS patients used marijuana, while another article found that that 21% of 160 epilepsy patients reported using marijuana in the past year. Of those epilepsy patients, 68% say the drug made seizures less severe and 54% said seizures were less frequent.
Scientists don’t put much faith in reports from patients unless a drug’s effects can be measured by a physician, Benson says. Patients may feel better not because of marijuana, but because of the «placebo effect,» in which ineffective drugs appear to produce results.

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