Researchers Find No Marijuana-Cancer Link

Washington Post : No link between marijuana and lung cancer

Researchers surprised to find no link between marijuana, cancer.

Study's findings apply even to heavy pot smokers...

By Mark Kaufman
Washington Post

The largest study of its kind has unexpectedly concluded that smoking marijuana, even regularly and heavily, does not lead to lung cancer. The new findings "were against our expectations" said Dr. Donald Tashkin, who has studied marijuana for 30 years.

"We hypothesized that there would be a positive association between marijuana use and lung cancer and that the association would be more positive with heavier use," he said. "What we found instead was no association at all, and even a suggestion of some protective effect."

Federal health and drug enforcement officials have widely used Tashkin's previous work on marijuana to make the case that the drug is dangerous. Tashkin said that while he still believes marijuana is potentially harmful, it's cancer-causing effects appear to be of less concern than previously thought.

Earlier work established that marijuana does contain cancer causing chemicals as potentially harmful as those in tobacco, he said. However, marijuana also contains the chemical THC, which he said may kill aging cells and keep them from becoming cancerous.

Tashkin's study, funded by the National Institutes of Health's National Institutes of Drug Abuse, involved 1,200 people, matched by age, sex, lifestyle and neighborhood. They were asked about their lifetime use of marijuana, tobacco and alcohol. The heaviest marijuana smokers had lit up more than 22,000 times, while moderately heavy usage was defined as smoking 11,000 to 22,000 marijuana cigarettes. Tashkin found that even the very heavy marijuana smokers showed no increases incidence of the three cancers studied. "This is the largest case-control study ever done, and everyone had to provide information about their marijuana use," he said." The study was limited to people younger than 60 because those older than that were generally not exposed to marijuana use in their youth, when it is most frequently tried.

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