The smoking of cannabis is the most harmful method of consumption, as the inhalation of smoke from organic materials can cause various health problems.
By comparison, studies on the vaporization of cannabis found that subjects were "only 40% as likely to report respiratory symptoms as users who do not vaporize, even when age, sex, cigarette use, and amount of cannabis consumed are controlled." Another study found vaporizers to be "a safe and effective cannabinoid delivery system."
While a study in New Zealand of 79 lung-cancer patients suggested daily cannabis smokers have a 5.7 times higher risk of lung cancer than non-users, another study of 2252 people in Los Angeles failed to find a correlation between the smoking of cannabis and lung, head or neck cancers. Some studies have also found that moderate cannabis use may protect against head and neck cancers, as well as lung cancer. Some studies have shown that cannabidiol may also be useful in treating breast cancer. These effects have been attributed to the well documented anti-tumoral properties of cannabinoids, specifically tetrahydrocannabinol (THC) and cannabidiol.