Effects of Second Hand Marijuana Smoke

by Richard Liang

Figure 1: Second hand smoke from marijuana may be just as harmful as second hand smoke from tobacco.


Though it is known that second hand smoke from tobacco is extremely detrimental to one’s health, second hand marijuana smoke is often seen as less harmful. However, a recent study led by Dr. Xiaoyin Wang and his team of researchers from the Cardiology Division of The University of California supports the theory that second hand marijuana smoke might not be so harmless after all.

The experiment involved two groups of rats, one that was exposed to second hand marijuana smoke and another that was exposed to second hand tobacco smoke. To simulate real-world conditions, 35 mL of smoke was administered to each group every two seconds. The femoral artery flow-mediated dilation (FMD) of the rats was monitored as an indicator of vascular health. If the endothelium, or the inner lining of blood vessels, is able to constrict and dilate in a normal manner, a normal FMD is produced. If the endothelium of blood vessels is damaged by something like smoke, then the FMD will be impaired. The FMDs of all the rats were measured before and after exposure to their respective type of second hand smoke.

The results suggested that both second hand marijuana and second hand tobacco smoke have similar detrimental cardiovascular effects. It seems that tetrahydrocannabinol (THC), the active ingredient in marijuana, does not play a role in FMD impairment; rather, common chemicals or ultrafine particles found in any kind of smoke, including diesel exhaust, candle smoke and incense smoke, were found to cause more damage. This was hypothesized because THC free marijuana yielded a similar result to marijuana with THC. Exposure to second hand marijuana smoke for one minute impaired FMD for 90 minutes, while exposure to second hand tobacco smoke for one minute impaired FMD for 30 minutes. From these results, it can be seen that marijuana smoke has detrimental cardiovascular effects similar to, or even worse than, tobacco smoke. Though further research may be necessary, individuals should be mindful of the smoke that they are breathing.  


  1. X. Wang, et al., One minute of marijuana secondhand smoke exposure substantially impairs vascular endothelial function. Journal of the American Heart Association, (2016). doi: 10.1161/JAHA.116.004004
  2. Image retrieved from: https://pixabay.com/static/uploads/photo/2013/05/12/18/55/cigarette-110849_1280.jpg

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