No Link Between Pot Smoking, Cancer Wed Oct 19, 7:02 PM ET WEDNESDAY, Oct. 19 (HealthDay News) -- Even though they're chemically similar, marijuana smoke is less likely than tobacco smoke to cause cancer, according to one expert review of the literature. The review, by Dr. Robert Melamede of the University of Colorado, Colorado Springs, noted that tobacco and marijuana smoke differ in a number of ways, particularly in the fact that marijuana smoke contains tetrahydrocannabinol (THC) , while tobacco smoke contains nicotine. Nicotine increases the cancer-promoting effects of smoke, while THC reduces those effects, he explained. And even though THC and nicotine act on related cellular pathways, they bind to different receptors to activate these pathways, the review found. Cells in the lungs and respiratory passages are lined with nicotine receptors but these cells don't appear to have THC receptors. This may explain why smoking marijuana has so far not been linked with lung cancer, a major cause of death from cigarette smoking. Research has also shown that marijuana kills cancer cells and reduces tumor growth. This is, in part, because marijuana reduces the formation of blood vessels that nourish tumors. However, the review warned that the effects of marijuana are complex and sometimes contradictory. It also noted that many people use marijuana and tobacco together, and the two drugs may interact in complex ways. While some governments are reluctant to approve marijuana for medicinal use, the review noted that there's increasing evidence that marijuana can improve the lives of patients with a broad range of health problems, including insomnia, AIDS, multiple sclerosis and Alzheimer's disease. The review will be published in an upcoming issue of the journal Harm Reduction.