Smoking hazards are touted as the final word condemning medical marijuana by prohibitionists intent on denouncing the medical utility of cannabis. That argument lacks substance, however, as cannabis is now known to have specific characteristics that minimize the risks of smoking, and also because an increasing number of marijuana patients now choose alternative methods of ingestion that do not rely on combustion.
Tobacco has dramatic negative consequences for those who smoke it. In addition to its high addiction potential, tobacco is causally associated with over 400,000 deaths yearly in the United States, and has a significant negative effect on health in general. More specifically, over 140,000 lung-related deaths in 2001 were attributed to tobacco smoke. Comparable consequences would naturally be expected from cannabis smoking since the burning of plant material generates a large variety of compounds that possess numerous biological activities. However, it is important to remember that tobacco is carcinogenic even when chewed or absorbed without inhaling tobacco smoke. Chewing tobacco is known to promote cancer of the mouth, for example, while cannabis is proven to have no such cancer-causing properties.
While cannabis smoke has been implicated in respiratory dysfunction, including the conversion of respiratory cells to what appears to be a pre-cancerous state; cannabis smoke has not been causally linked with tobacco related cancers such as lung, colon, or rectal cancers. Recently, Hashibe, et al carried out an epidemiological analysis of marijuana smoking and cancer. A connection between marijuana smoking and lung or colorectal cancer was not observed. These conclusions were reinforced by the recent work of Tashkin and coworkers who were unable to demonstrate a link between cannabis smoke and lung cancer.
Furthermore, compounds found in cannabis have been shown to kill numerous cancer types including: lung cancer, breast, and prostate cancer, leukemia, lymphoma, glioma, skin cancer, and pheochromocytoma. The effects of cannabinoids are complex and sometimes contradicting, often exhibiting biphasic responses. For example, in contrast to the tumor killing properties mentioned above, low doses of THC may stimulate the growth of lung cancer cells in vitro. Nonetheless, it is clear that no cases of smoke-related cancers have ever been documented.
Smoking methods and materials vary widely among cannabis users. Gauging the effects of marijuana smoke on the lungs and respiratory system is extremely difficult due to the wide variety of smoking techniques. The many variables apparent in evaluating the respiratory risks of smoking cannabis include not only the method of inhalation but also the potency and purity of the product consumed.
Smoking properly cultivated, high-potency cannabis using a dual action hot/cold water pipe may lessen tar intake without reducing delivery of medicinal compounds, according to Dr. Lester Grinspoon, M.D. Conventional water pipes, however, do little to lower the ratio of tar to THC. The hand-rolled cigarette (joint), presents a much lesser health risk than do all types of conventional pipes. Marijuana cigarettes burn at lower temperatures than most pipes, reducing the potential for heat damage to respiratory tissues. With the advent of hemp rolling papers, even the questionable residue of wood paper may be avoided. In the future, developments in vaporizer technology offer a potentially risk-free method of inhalation by vaporizing medicinal cannabinoids without burning the plant material.  Unfortunately, legal complications and enforced ignorance stymie this harm-reduction technology. Dr. Grinspoon submitted information to the Institute of Medicine on prototype vaporizers prior to its Marijuana and Medicine report, yet, in the words of Tod Mikuriya, M.D., the federal government's highest medical authority "pointedly chose to omit" any reference to the smokeless marijuana vaporizers.
Cannabis prohibition severely cripples both scientific research and public information on risk-free smoking methods. Additionally, legislation outlawing "drug paraphernalia" reduces public access to safer smoking techniques. To complicate the matter even firther, popular media portrayals commonly support the misconception that marijuana smokers should inhale deeply to gain the greatest effect. While novice smokers might mistake the symptoms of hyperventilation for the subtle psychoactive qualities of THC, experienced cannabis users eventually discover that all smoking methods are more advantageous when performed with less vigor.
Cannabinoids are fat-soluble and readily absorbed by the respiratory system, entering the bloodstream almost immediately upon contact. In fact, cannabinoids are so easily assimilated that second-hand smoke can cause one to test positive in a urinary drug screening after just 20 minutes of passive exposure. , ,  Tars and other smoke by-products, on the other hand, are not fat-soluble and require comparatively prolonged saturation to penetrate soft lung tissue. Therefore, inhaling deeply and holding the smoke in the lungs for more than a few seconds is not only useless, it also causes greater exposure to toxic substances. To achieve the greatest medical benefits of inhaled cannabis smoke, then, the optimum method is a few seconds of moderate inhalation.
Dr. Gregory T. Carter of the University of Washington writes:
"Despite risk for bronchitis, the main advantage of smoking is rapid onset of effect and easy dose titration. When marijuana is smoked, cannabinoids in the form of an aerosol in the inhaled smoke are rapidly absorbed and delivered to the brain, as would be expected of a highly lipid-soluble drug. However, smoking anything, including marijuana, carries health risks for the lungs and airway system. A healthier option is vaporization. Because the cannabinoids are volatile, they will vaporize at a temperature much lower than actual combustion. Heated air can be drawn through marijuana and the active compounds will vaporize, which can then be inhaled. This delivers the substance in a rapid manner that can be easily titrated to desired effect. Vaporization therefore removes most of the health hazards of smoking." 
Note: an advisable regimen for patients concerned about potential health risks associated with smoking cannabis includes the daily intake of a multiple B-complex vitamin supplement and a basic antioxidant formula including one mixed carotene supplement, 400-800 IU of natural vitamin E, 200 micrograms of selenium, and 1,000 to 2,000 mg of vitamin C taken two to three times per day.
Any potentially deleterious effects of cannabis smoke may be complete avoided through various methods of oral ingestion.
Related sections: Cancer, Contaminants, Immune Responses, Respiratory Disease, Toxicity, Upper Respiratory Infection.
 " Cananbis and tobacco smoke are not equally carcinogenic", Robert Melamede, Harm Reduction Journal, 18 Oct., 2005 (See: Abtracts and Studies section of this website)
 Gieringer, “Marijuana Water Pipe and Vaporizer Study.” MAPS bulletin, 1996, CANORML, http://www.norml.org/canorml/
 Wishnia, “The IOM Medical-Marijuana Report.” High Times, July, 1999
 Geiringer, op. cit.
 Mason, Perez-Reyes, McBay, and Folz, “Cannabinoid concentrations in plasma after passive inhalation of marijuana smoke.” Journal of Analytical Toxicology, Vol. 4, pp. 172-174, July 7, 1983
 In another study, passive study to exposure of 16 cannabis cigarettes over a six day period was shown to equal one cannabis cigarette actively smoked, Source: Cone and Johnson, “Contact highs and urinary cannabinoid excretion after passive exposure to marijuana smoke.” Clinical Pharmacological Therapy, Vol. 40, No. 3, pp. 247-256, September 1986
 Amtmann, Weydt, Johnson, Jensen, Carter, “Survey of Cannabis Use in Patients with Amyotrophic Lateral Sclerosis.” Source: Cannabis MD, www.cannabismd.org/reports/carter4.php
 “Ask Andrew Weil.” Health questions answered online, http://www.cgi.pathfinder.com/drweil/