And the last I heard, oxygen was "combustible". Inhaling a combustible isn't a health risk; inhaling combustion products might be. But many pot smokers use a vape, set to well-below the combustion temperature for their chosen herb.
Vapes have issues too, which include exposure to heavy metals. By combustibles I mean anything you burn. Again, not a doctor and not a medical scientist so I may be using the wrong words but most people who use weed know these things. Most notably, anything that is smoked will incur a small but sharp rise in blood pressure. If you wear a heart monitor (or wrist watch with one) it's fairly trivial to detect.
- the possibility of psychosis or schizophrenia in people 16-35 (https://medicine.yale.edu/psychiatry/step/resources/Cannabis...)
- the same risk that inhaling any combustible has
- overeating
- cannabinoid hyperemesis syndrome (https://www.cedars-sinai.org/health-library/diseases-and-con...)
For some people the benefits outweigh the risks, especially when practiced in moderation.