We have plenty of research looking at chronic smokers of numerous decades, and the consensus is that there is no relationship between cannabis smoking and developing cancer.
Smoke from the combustion of any plant material, be it tobacco, cannabis or a leaf from the tree outside, produces a lot of toxins and carcinogens. Even sitting next to a wood-fueled campfire will lead to exposure to these substances, resulting in compromised cardiovascular function and other negative health effects. The pattern of abnormalities associated with cannabis smoking, as has been discovered thus far, seems to differ from tobacco smoking. Smoking anything at all is unhealthy, and if alternative methods of consumption are available, they’re highly recommended above smoking.
An important distinction to make here is that the negative side effects of cannabis smoking comes specifically from the combustion of plant matter, not the inhalation of phytocannabinoids, such as THC (the one that makes you high) and CBD. Cardiovascular issues are observed even in studies where all phytocannabinoids have been removed from the smoke inhalation. Alternative methods of smoking cannabis, such as vaporization, edibles, capsules, tinctures, transdermal patches, concentrates and more should be considered if one wishes to avoid the negative side effects.
Cannabis smoke differs from that of tobacco in a few notable ways. It contains roughly 20 times more ammonia, 5 times more hydrogen cyanide and nitrogen oxides, but lower levels of carcinogenic polycyclic aromatic hydrocarbons (PAHs). Some studies have refuted the drastically higher ammonia and hydrogen cyanide levels, finding relatively similar levels to that of tobacco, but all studies conclude that there’s less PAHs. Specifically, the carcinogens benzene, naphthalene and toluene have been found in cannabis smoke. Benzene is formed during the natural processes of combustion and can be damaging to the reproductive system when inhaled in very large quantities. Naphthalene is a potential carcinogen, and research on it is lacking. In high concentrations, it’s been shown to destroy red blood cells, and in one severe case was shown to cause organ damage. Toluene is a benzene derivative, though thankfully far less toxic. Overexposure to this compound has been shown to have negative effects on the central nervous system (CNS), as well as symptoms of headaches, nausea, fatigue, sleepiness and irritation of the eyes and upper respiratory tract. An important reminder is that traditional smoking of marijuana will not guarantee any of the above issues; those studies were done under specific circumstances involving unrealistically large amounts of carcinogens, much more than would be produced in traditional smoking, even when taken to the extreme.
Recent research has indicated that secondhand cannabis smoke impairs the cardiovascular system even more than secondhand tobacco smoke. It impairs the blood vessels’ ability to dilate, and seems to last longer for cannabis smoke than it does for tobacco smoke. It’s important to note that the chemical activity of cannabis smoke decreases very quickly once exhaled, meaning you would need to be inhaling cannabis smoke almost immediately after the exhalation of the smoker. Simply smelling smoked cannabis is not the same as secondhand smoke.
Even with these facts laid out, it’s simply unfair to compare cannabis smoke to tobacco smoke when you look at the effects caused by long-term smoking. A 2016 study examining chronic marijuana smokers, those consuming a few times a day for more than 20 years, found the only negative health effect to be an increased risk of periodontal disease, a gum infection that can destroy the jawbone if left unchecked. This condition is treatable and typically clears up in a few months. Contrarily, tobacco kills over 480,000 people in the US every year, more than firearms, motor vehicle accidents, HIV, alcohol and all illegal drug overdoses combined. There has never been a verified report of a death from cannabis since mankind began writing, including smoking.
Comprehensive and extensive research has been conducted on tobacco smoke, linking it to an array of lung issues, most drastically lung cancer. In contrast, studies conducted thus far have found no link between cannabis smoking and lung cancer, emphysema and respiratory infection. A number of well-designed epidemiologic studies suggest that the risk for lung or otherwise-related cancers from cannabis smoke is far lower than that of tobacco, though a meta-analysis of 19 studies conducted in 2006 found no correlation between heavy marijuana use and lung cancer when factoring out tobacco use. In 2012, Dr. Donald Tashkin, professor of medicine at UCLA, conducted a study examining 5,115 young adults over the course of 20 years, beginning in 1985, and found that marijuana smoke as a whole did not affect the rate of lung cancer among frequent users.
Further research suggests that the phytocannabinoids, like THC and CBD, found in the smoke alongside carcinogens may play a role in the lack of cancer from heavy marijuana smokers. Numerous phytocannabinoids and terpenes found in cannabis have been shown to have anticancer and antioxidant properties, and may counteract many of the carcinogens that are also inhaled while smoking.
Another key way that cannabis smoke differs from that of tobacco is its effects on the immune system. In general, cannabis has anti-inflammatory and immuno-suppressive effects, which are beneficial to patients suffering from inflammatory diseases such as inflammatory bowel disease or multiple sclerosis. On the other hand, since regular cannabis smoking causes airway issues, the immuno-suppressive effects may leave regular smokers more susceptible to respiratory infections. This is another area that requires much more research than the US Government is willing to allow. The anti-inflammatory and immuno-modulatory capacity of phytocannabinoids are well established, and these agents have a broad therapeutic potential in various inflammatory diseases, including cardiovascular diseases.
To recap the discoveries of dozens of scientific studies and papers done on this subject, overall, the negative effects of smoking cannabis are much lower than that of tobacco in regards to lung health. Regular cannabis smoking can cause physical airway damage and is associated with an increased risk of periodontal disease. Secondhand cannabis smoke exposure leads to impairments in cardiovascular function. There is no compelling evidence that cannabis smoke leads to obstructive airway disease or emphysema, and evidence suggests it helps to reduce arterial plaque and reduce the inflammation that causes it. A number of high-quality studies have failed to find a link between cannabis smoking and lung or upper airway cancers for occasional, moderate or chronic consumers. To date, despite decades of research, a link between cannabis smoking and lung cancer has never been found. Alternative methods of cannabis consumption, such as vaporizers, edibles, tinctures and more, do not carry any of the risks associated with cannabis smoke inhalation.