"In conclusion, while both tobacco and cannabis smoke have similar properties chemically, their pharmacological activities differ greatly. Components of cannabis smoke minimize some carcinogenic pathways whereas tobacco smoke enhances some. ... [C]urrent knowledge does not suggest that cannabis smoke will have a carcinogenic potential comparable to that resulting from exposure to tobacco smoke."
Unlike tobacco smoke exposure, cannabis smoke exposure - even long-term - is not positively associated with cancers of the lung or upper aerodigestive tract
"Despite the presence of carcinogens in marijuana smoke in concentrations comparable with those that are found in tobacco smoke, the weight of evidence from well-designed epidemiologic studies does not support the concept that habitual marijuana use in the manner and quantity in which it is customarily smoked, when adjusted for tobacco, is a significant risk factor for the development of lung cancer."
"To investigate the association between cannabis smoking and lung cancer risk, data on 2,159 lung cancer cases and 2,985 controls were pooled from 6 case-control studies in the US, Canada, UK, and New Zealand within the International Lung Cancer Consortium. ... Compared to non-habitual or never users, the summary OR was 0.88 for individuals who smoked 1 or more joint-equivalents of cannabis per day and 0.94 for those consumed at least 10 joint-years. ... Results from our pooled analyses provide little evidence for an increased risk of lung cancer among habitual or long-term cannabis smokers."
"We conducted a population-based case-control study of the association between marijuana use and the risk of lung and upper aerodigestive tract cancers in Los Angeles. ... Although using marijuana for > or =30 joint-years was positively associated in the crude analyses with each cancer type (except pharyngeal cancer), no positive associations were observed when adjusting for several confounders including cigarette smoking. ... Our results ... suggest that the association of these cancers with marijuana, even long-term or heavy use, is not strong and may be below practically detectable limits."
"We hypothesized that there would be a positive association between marijuana use and lung cancer, and that the association would be more positive with heavier use. What we found instead was no association at all, and even a suggestion of some protective effect."
"The purpose of this retrospective cohort study was to examine the relationship of marijuana use to cancer incidence. The study population consisted of 64,855 examinees in the Kaiser Permanente multiphasic health checkup in San Francisco and Oakland (California, United States), between 1979-85. ... Follow-up for cancer incidence was conducted through 1993 (mean length 8.6 years). Compared with nonusers/experimenters (lifetime use of less than seven times), ever- and current use of marijuana were not associated with increased risk of cancer of all sites in analyses adjusted for sociodemographic factors, cigarette smoking, and alcohol use. Marijuana use also was not associated with tobacco-related cancers or with cancer of the following sites: colorectal, lung, melanoma, prostate, breast, cervix. ... We conclude that, in this relatively young study cohort, marijuana use and cancer were not associated in overall analyses."
Cannabis smoke exposure, even long-term, is not associated with the sort of significant adverse pulmonary effects associated with tobacco - such as COPD.
"[I]t has been pragmatic to assume that cannabis and tobacco would have similar respiratory effects. ... The research that has been done, however, offers a different story. The most common serious respiratory consequences from smoking tobacco are Chronic Obstructive Pulmonary Disease (COPD) and lung cancer. Epidemiological evidence that smoking cannabis causes either of these is scant."
"Although regular smoking of marijuana is associated with an increased risk of symptoms of chronic bronchitis and evidence of inflammation and injury involving the larger airways, lung function findings, although mixed, do not provide compelling evidence that habitual marijuana smoking in the manner and amount that it is generally smoked increases the risk of COPD, at least at the population level."
"Neither current nor former marijuana use was associated with increased risk of cough, wheeze, or chronic bronchitis when compared to never marijuana users. ... Current and former marijuana smokers had significantly higher FEV1 (forced expiratory volume) ... when compared to never users. ... Both current and former marijuana use was associated with significantly less quantitative emphysema ... when compared to never users, even after adjusting for age, ... current tobacco smoking pack years, and BMI. ... In agreement with other published studies, we also did not find that marijuana use was associated with more obstructive lung disease. ... Among older adults with a history of tobacco use, marijuana use does not appear to increase risk for adverse lung function. ... There may be no to little increased risk of marijuana use for a further increase in respiratory symptoms or adverse effects ... among those with a history of concomitant tobacco use."
"[T]he pattern of marijuana's effects seems to be distinctly different when compared to that of tobacco use. ... In a large cross-section of U.S. adults, cumulative lifetime marijuana use, up to 20 joint-years, is not associated with adverse changes in spirometric measures of lung health."
"[H]abitual use of marijuana alone does not appear to lead to significant abnormalities in lung function. Findings from a limited number of well-designed epidemiological studies do not suggest an increased risk of either lung or upper airway cancer from light or moderate use. ... Overall, the risks of pulmonary complications of regular use of marijuana appear to be relatively small and far lower than those of tobacco smoking."
"Cannabis smoking is not equivalent to tobacco smoking in terms of respiratory risk. ... [C]annabis smoking does not seem to increase risk of chronic obstructive pulmonary disease (COPD) or airway cancers. In fact, there is even a suggestion that at low doses cannabis may be protective for both conditions."
"In this 20-year study of marijuana and pulmonary function, we confirmed the expected reductions in FEV1 (first second of expiration) and FVC (forced vital capacity) from tobacco use. In contrast, marijuana use was associated with higher FEV1 and FVC at the low levels of exposure typical for most marijuana users. With up to 7 joint-years of lifetime exposure (e.g., 1 joint/d for 7 years or 1 joint/wk for 49 years), we found no evidence that increasing exposure to marijuana adversely affects pulmonary function. ... Occasional and low cumulative marijuana use was not associated with adverse effects on pulmonary function."
"On the basis of my own work and a systematic and thorough review of the relevant literature on this subject, I have come to the conclusion that regular marijuana smoking does not lead to COPD and is not a significant risk factor in the development of lung or aerodigestive tract (head and neck) cancer, in contrast to the wealth of evidence implicating tobacco smoking as the major risk factor for both COPD and respiratory cancer."
Vaporization -- which heats marijuana to a point where cannabinoid vapors form - mitigates consumers exposure to potential respiratory hazards, such as the inhalation of combustive smoke or exposure to unwanted particulate matter
"[T]he four electrically-driven and temperature-controlled vaporizers investigated in this study efficiently decarboxylate acidic cannabinoids and release reliably the corresponding neutral cannabinoids into the vapor. Therefore, they can be considered as a promising application mode for the safe and efficient administration of medicinal cannabis and cannabinoids."
"The vapourizer runs heated air across the plant without igniting it, releasing the cannabinoids in a vapour free from the byproducts of combustion. ... Laboratory work shows that cannabis vapour is composed almost exclusively of cannabinoids with virtually no pyrolitic compounds. The vapourizer raises cannabinoid levels in humans but does not raise exhaled CO levels. In short, vapourizers show promise for cannabis users who want to avoid pulmonary problems and prefer a more rapid onset than edibles provide."
"Four cannabis users who reported respiratory symptoms (including two tobacco smokers) agreed to stop smoking cannabis and use the vaporizer for 1 month. ... After 1 month of vaporizer use, self-reported respiratory symptoms improved dramatically. ... These results suggest that the cannabis vaporizer is acceptable to users, and has the potential to decrease cannabis-related respiratory problems."
"The aim of the study was to investigate vaporization using the Volcano((R)) device as an alternative means of delivery of inhaled Cannabis sativa. ... CO (carbon monoxide) levels were reduced with vaporization. No adverse events occurred. Vaporization of cannabis is a safe and effective mode of delivery of THC."
"Vaporizers heat cannabis to release active cannabinoids, but remain cool enough to avoid the smoke and toxins associated with combustion. ... We examined self-reported respiratory symptoms in participants who ranged in cigarette and cannabis use. Data from a large Internet sample revealed that the use of a vaporizer predicted fewer respiratory symptoms even when age, sex, cigarette smoking, and amount of cannabis used were taken into account."
"The goal of this study was to evaluate the performance of the Volcano vaporizer in terms of reproducible delivery of the bioactive cannabinoid tetrahydrocannabinol (THC). ... Our results show that with the Volcano a safe and effective cannabinoid delivery system seems to be available to patients. The final pulmonal uptake of THC is comparable to the smoking of cannabis, while avoiding the respiratory disadvantages of smoking."