Research funded by the National Institute on Drug Abuse (NIDA) suggests that secondhand smoke from marijuana could be at least as harmful to individuals' cardiovascular health as secondhand tobacco smoke, and perhaps more so.
Published in the Journal of the American Heart Association, the pre-clinical study using rats found that one minute of exposure to secondhand marijuana smoke generated levels of impairment in flow-mediated dilation (FMD) similar to those from secondhand tobacco smoke. FMD refers to the extent to which arteries enlarge in response to increased blood flow.
However, the study also found that FMD remained impaired for at least 90 minutes after a minute of exposure to secondhand marijuana smoke, whereas impairment following secondhand tobacco smoke is generally resolved within 30 minutes.
The background section of the study's abstract states, “Lack of evidence for marijuana [secondhand smoke] causing acute cardiovascular harm is frequently mistaken for evidence that it is harmless, despite chemical and physical similarity between marijuana and tobacco smoke.”
NIDA states that more research is necessary in order to quantify levels of secondhand marijuana exposure under various real-world situations.