As other commenters have noted, the study misses an important fourth: vaporized THC products. Nicotine is common to e-cigarettes and cigarettes; combustion byp

As other commenters have noted, the study misses an important fourth: vaporized THC products. Nicotine is common to e-cigarettes and cigarettes; combustion byproducts are common to cannabis and tabacco smoke. There shouldn't be much overlap between cannabis smoke and e-cigarettes, because the latter isn't meant to be combusted. Likewise, people vaporize THC below its combustion point, so it shouldn't have much overlap with nicotine products. My suspicion (as a casual user of all of the above) is that there isn't one "smoking gun" (pun intended) but putting anything other than clean fresh air into your lungs is probably bad for your heart because blood travels directly from the lungs to the heart before it passes through the liver.