A vast study conducted by UCLA produced surprising results - smoking marijuana, even regularly and heavily, does not lead to lung cancer. The leader of the UCLA team, Dr. Donald Tashkin, said that they "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...What we found instead was no association at all, and even a suggestion of some protective effect."

Earlier works have found out that marijuana contain cancer-causing chemicals, potentially as harmful as those in tobacco. But they also found out that it also contains the chemical THC, which may kill aging cell and keep them from becoming cancerous.

The study involved 1,200 people in the L.A. area who had lung, neck, or head cancer, and another 1,040 people without cancer matched by age, sex, and neighborhood. The study was limited to people younger than 60 because those older folks were generally not exposed to marijuana use during their youth.

The group was then asked about their lifetime use of weed, cigarettes, and alcohol. Tashkin and his team found out that the very heavy marijuana users (who lit up more than 22,000 times) showed no increased incidence of lung, neck, or head cancer. When asked to explain why other studies found links between marijuana use and cancer, he mentions that most of these previous studies used smaller human studies and lab animals.