Type to search

Cannabis Supporting Your Practice

Second-hand Cannabis Smoke: What (little) We Know So Far


Cannabis has been legal across Canada for six months. Meanwhile consumers and health professionals continue to ask questions about the health effects and long-term implications of using cannabis, particularly when it is inhaled second-hand.

In August of 2018, prior to legalization, the Canadian Medical Association Journal Open published the results of a systematic review led by Dr. Fiona Clement, Associate Professor and researcher at the University of Calgary, about the effects of second-hand cannabis smoke. While the study garnered attention for its finding that second hand “toke” could cause an individual to fail a drug test, it also suggests second-hand cannabis smoke could be harmful to our health and that more research is needed.

What We Know

According to Dr. Clement’s review, a person exposed to second hand smoke in a poorly ventilated and closed room could test positive for THC, and that THC is detectable in the body after 15-minutes of second-hand exposure. While the literature review does not replicate a real-life exposure situation, Clement described a relatable real world situation in an interview with Toronto City News  where an “…enclosed space maybe the size of a regular kitchen, all of the windows closed, relatively poor ventilation, and a joint being passed around while you’re having a conversation. People who are passively exposed, so not smoking themselves, can test positive in their blood or urine for THC levels above 5 nanograms per millilitre, which is being put out as the legal limit, with relatively modest exposure conditions.”

Early Recommendations

A position statement issued by president of The Canadian Lung Association reaffirms that, “There are still many unknowns about cannabis and its long-term effects on lung health, but we do know that the inhalation of smoke is harmful to lung health as the combustion of materials releases toxins and carcinogens. The statement also adds that, “Second-hand cannabis smoke contains many of the same toxins and chemicals found in directly inhaled cannabis smoke.

Acknowledging that more research is needed, The Canadian Lung Association remains concerned about the potential harmful effects of second-hand cannabis smoke.

The Ontario Lung Association is also warning of the possible health effects of second-hand cannabis smoke pointing out that cannabis contains many of the same metals, chemicals, and particulates as tobacco smoke with 33 of them being known carcinogens.

More Research Needed

Dr. Clement and her team emphasize that biologically, there is no way to prove THC levels are the result of second-hand smoke rather than active consumption. And though their research does suggest that second-hand cannabis smoke, though different in concentration of its components, is similar to second-hand tobacco smoke, she underscored that at this time, there is not enough published research to know how cannabis smoke compares to tobacco smoke.

We want to hear from you!

Leave a comment about this post in the box below, send your feedback by email, or call us at 1-855-716-2747.

Until next time!

CDA Oasis Team


Leave a Comment

Your email address will not be published. Required fields are marked *

%d bloggers like this: