What Happens When You Breathe in Someone Else's Marijuana Smoke

Systematic review searching 6 databases from inception to October 2017. Abstract and full-text review were conducted in duplicate. Included studies were human, in vivo, or in vitro with more than one case, published in English or French, reporting original quantitative data. Study quality was assessed using the Downs and Black checklist. 15 studies met inclusion criteria from 1,701 abstracts.

As marijuana legalization expands, secondhand smoke becomes a public health policy question analogous to tobacco. This review provides the evidence base for policies around where marijuana can be smoked, with implications for shared housing, public spaces, and workplace regulations.

The authors recommend aligning marijuana and tobacco smoking bylaws as the most effective policy approach. This is notable because it implies marijuana secondhand smoke should be treated with the same public health seriousness as tobacco secondhand smoke, even though the specific health risks may differ.

All included studies were rated good to poor quality. No evidence was found on long-term exposure effects or third-hand smoke. The 15 included studies used varied methodologies and exposure conditions, making direct comparison difficult.