In a major policy controversy that may ultimately rival that surrounding public e-cigarette use, communities around the country and world are grappling NOW with whether public smoking bans should include marijuana, and whether leaf vaporization of marijuana or tobacco is less harmful than combustion.  In this project, we will ask whether multiple brief exposures to tobacco and marijuana secondhand smoke (SHS) cause lasting damage to cardiovascular health, and if exposure to non-combustion leaf “vaporization” products from tobacco and marijuana is less harmful to vascular health than exposure to smoke. 

We and others have demonstrated that short exposures to tobacco SHS, as brief as one minute, can cause transient drops in blood vessel function, specifically a property of arteries called FMD that enables them to rapidly grow in diameter when more blood needs to be passed the limbs or heart.  FMD is important in maintaining the health of arteries.  Impairment of FMD can increase the risk of atherosclerosis in the long term, as well as the risk of heart attack and stroke.  In humans who are exposed frequently to SHS, FMD is chronically impaired; therefore, it is likely that multiple brief insults cause long-term vascular health problems.  Using a rat model of blood vessel function with great similarity to human blood vessel function, we have shown that marijuana SHS has a similar effect on vascular function than tobacco SHS that takes longer to recover, with a one-minute exposure leading to substantial impairment of FMD that lasts for at least 90 minutes.  Our results indicate that combustion products in smoke from either tobacco or marijuana, rather than nicotine or cannabinoids, are responsible for this harmful effect.  Media reports of our results have already stimulated much public debate about whether it may be safer to use vaporizers for marijuana (the kind that slowly heats the plant material instead of burning it), and tobacco companies have also been attempting to introduce similar products for tobacco that may be safer than combustible cigarettes.  (E-cigarettes, which aerosolize liquid solutions of nicotine or THC, are a different product.)  The leaf vaporization approach may or may not avoid the combustion products that lead to the vascular harm. 

The public, clinicians, and policy makers need to know the extent of potential harm caused by both tobacco and marijuana SHS, to ensure that increasing marijuana legalization does not undo decades of progress of smoke-free laws and smoking denormalization; and it is important to determine whether people who use leaf vaporizers face the same acute vascular risks as those who smoke or inhale SHS.  Our findings will be actively disseminated to the community, clinicians, policy advocates, regulators, politicians, and journalists.