In an interview with Reuters, Melamede explained that while nicotine has several effects that promote lung and other types of cancer, THC acts in ways that counters the cancer-causing chemicals in marijuana smoke. "THC turns down the carcinogenic potential," he said. Melamede reviewed the scientific evidence in a recent issue of Harm Reduction Journal.
Lab research indicates that nicotine activates an enzyme in the body that converts certain chemicals in both tobacco and marijuana smoke into cancer-promoting form. But studies in mice suggest that THC blocks this enzyme activity.
Another key difference is in the immune system effects of tobacco and marijuana, Melamede said. Smoke sends irritants into the respiratory system, triggering an immune-regulated inflammatory response that involves the generation of potentially cell-damaging substances called free radicals. But cannabinoids – both those found in marijuana and versions found naturally in the body – have been shown to reduce this inflammatory response.
COLORADO SPRINGS – Both marijuana and tobacco smoke contain cancer-causing chemicals, but a report by University of Colorado researcher Robert Melamede concludes that tetrahydrocannabinol (THC), the active ingredient in marijuana, seems to keep it from promoting lung cancer.