Research: Marijuana smoke prevents cancer

It's official: herb is the healing of the nations.

"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, its 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.