users education

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."

Cannabis is ranked one of the least harmful drugs by a study published in the UK medical journal, The Lancet.

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.
Cannabis use has been assessed by several studies to be correlated with the development of anxiety, psychosis, and depression. A 2007 meta-analysis estimated that cannabis use is statistically associated, in a dose-dependent manner, to an increased risk in the development of psychotic disorders, including schizophrenia. No causal mechanism has been proven, however, and the meaning of the correlation and its direction is a subject of debate that has not been resolved in the scientific community. Some studies assess that the causality is more likely to involve a path from cannabis use to psychotic symptoms rather than a path from psychotic symptoms to cannabis use, while other studies assess the opposite direction of the causality, or hold cannabis to only form parts of a "causal constellation", while not inflicting mental health problems that would not have occurred in the absence of the cannabis use.
Though cannabis use has at times been associated with stroke, there is no firmly established link, and potential mechanisms are unknown. Similarly, there is no established relationship between cannabis use and heart disease, including exacerbation of cases of existing heart disease. Though some fMRI studies have shown changes in neurological function in long term heavy cannabis users, no long term behavioral effects after abstinence have been linked to these changes.