All Smoke Is Not Created Equal

Originally published at blog.NORML.org

Long-term exposure to tobacco smoke is demonstrably harmful to health. According to the United States Center for Disease Control, tobacco smoking is the leading cause of preventable death in the United States, and chronic exposure to tobacco smoke is linked to increased incidences of cancer as well as vascular disease. Inhaling tobacco smoke is also associated with a variety of adverse pulmonary effects, such as COPD (chronic obstructive pulmonary disease).

Does smoking cannabis pose similar dangers to lung health? According to a number of recent scientific findings, marijuana smoke and tobacco smoke vary considerably in their health effects. So then why are lawmakers in various states, such a Minnesota and New York, imposing new restrictions prohibiting the inhalation of herbal preparations of cannabis?

Marijuana Smoke vs. Tobacco Smoke

Writing in the Harm Reduction Journal in 2005, noted cannabis researcher Robert Melamede explained that although tobacco smoke and marijuana smoke have some similar chemical properties, the two substances possess different pharmacological activities and are not equally carcinogenic. Specifically, he affirmed that marijuana smoke contains multiple cannabinoids – many of which possess anti-cancer activity – and therefore likely exerts “a protective effect against pro-carcinogens that require activation.” Melamede concluded, “Components of cannabis smoke minimize some carcinogenic pathways whereas tobacco smoke enhances some.”

Marijuana Smoke and Cancer

Consequently, studies have so far failed to identify an association between cannabis smoke exposure and elevated risks of smoking-related cancers, such as cancers of the lung and neck. In fact, the largest case-controlled study ever to investigate the respiratory effects of marijuana smoking reported that cannabis use was not associated with lung-related cancers, even among subjects who reported smoking more than 22,000 joints over their lifetime. Summarizing the study’s findings in The Washington Post, pulmonologist Dr. Donald Tashkin, Professor Emeritus at the David Geffen School of Medicine at UCLA, concluded: “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.”

A meta-analysis of additional case-control studies, published in the International Journal of Cancer in 2014, similarly reported, “Results from our pooled analyses provide little evidence for an increased risk of lung cancer among habitual or long-term cannabis smokers,” while a 2009 Brown University study determined that those who had a history of marijuana smoking possessed a significantly decreased risk of head and neck cancers as compared to those subjects who did not.

Marijuana Smoke and Pulmonary Function

According to a 2015 study conducted at Emory University in Atlanta, the inhalation of cannabis smoke, even over extended periods of time, is not associated with detrimental effects on pulmonary function, such as forced expiratory volume (FEV1) and forced vital capacity (FCV). Assessing marijuana smoke exposure and lung health in a large representative sample of U.S. adults, age 18 to 59, they maintained, “The pattern of marijuana’s effects seems to be distinctly different when compared to that of tobacco use.” Subjects had inhaled the equivalent of one marijuana cigarette per year for 20 years, yet did not experience FEV1 decline or deleterious change in spirometric values of small airways disease.

Marijuana Smoke and COPD

While tobacco smoking is recognized as a major risk factor for the development of COPD – a chronic inflammation of the airways that may ultimately result in premature death – marijuana smoke exposure (absent concurrent tobacco smoke exposure) appears to present little COPD risk. In 2013, McGill University professor and physician Mark Ware wrote in the journal Annals of the American Thoracic Society: “Cannabis smoking does not seem to increase risk of chronic obstructive pulmonary disease or airway cancers… Efforts to develop cleaner cannabinoid delivery systems can and should continue, but at least for now, (those) who smoke small amounts of cannabis for medical or recreational purposes can breathe a little bit easier.”

Mitigating Marijuana Smoke Exposure

The use of a water-pipe filtration system primarily cools cannabis smoke, which may reduce throat irritation and cough. However, this technology is not particularly efficient at eliminating the potentially toxic byproducts of combustion or other potential lung irritants.

By contrast, vaporization heats herbal cannabis to a point where cannabinoid vapors form, but below the point of combustion – thereby reducing the intake of combustive smoke or other pollutants, such as carbon monoxide and tar. Observational studies show that vaporization allows consumers to experience the rapid onset of effect while avoiding many of the associated respiratory hazards associated with smoking – such as coughing, wheezing, or chronic bronchitis. Clinical trials also report that vaporization results in the delivery of higher plasma concentrations of THC (and likely other cannabinoids) compared to smoked cannabis. As a result, the authors affiliated with the University of California Center for Medicinal Cannabis Research and elsewhere now acknowledge that vaporizers provide a “safe and effective” way to for consumers to inhale herbal cannabis.

The Bottom Line

Based on this scientific record, it makes little sense for lawmakers to impose legislative bans on herbal cannabis products, such as those that presently exist for patients in Minnesota and New York and which are now being proposed in several other states (e.g., Georgia and Pennsylvania). Oral cannabis preparations, such as capsules and edibles, possess delayed onset compared to inhaled herbal cannabis, making these options less suitable for patients desiring rapid symptomatic relief. Further, oral administration of cannabis-infused products is associated with significantly greater bioavailability than is inhalation – resulting in more pronounced variation in drug effect from dose to dose (even in cases where the dose is standardized). These restrictions unnecessarily limit patients’ choices and deny them the ability to obtain rapid relief from whole-plant cannabis in a manner that has long proven to be relatively safe and effective.