They both put tar in your lungs. A tobacco smoker generally smokes far more cigarettes than a cannabis smoker. Per-breath, cannabis seems to put more tar in your lungs, since it's generally unfiltered. But a tobacco smoker takes many more breaths of smoke.

Some information here:

https://www.drugabuse.gov/publications/research-reports/mari...

As far as I can tell, vaping is far, far safer than inhaling smoke, for both tobacco and cannabis. The healthiest strategy is to avoid all of these things of course.

Nicotine is potentially harmful in a few ways but mostly it's the constituents of tobacco smoke, particularly nitrosamines: https://www.bbc.com/future/article/20121116-can-we-ever-have....

Nicotine is a harmless nootropic on the level of caffeine, it's inhaling combustion products that is the big problem.

Yes. This is a common misconception. It’s not that inhaling any kind of smoke is inherently dangerous. It’s specifically the oxidative damage that tobacco causes that makes it so uniquely deleterious. Reactive oxygen species are no joke.

By contrast cannabis is a natural anti-oxidant. Smoking cannabis might be correlated with more bronchitis but none of the cancer, heart disease, [insert every other tobacco harm]. BTW I seem to recall particle size is different between tobacco and cannabis smoke but I think the oxidative damage is the main reason