The harmful effects of tobacco are largely attributed to the hundreds of chemicals added to the product to ensure it burns at the right speed, to ensure it doesn't attract pests while growing, so it keeps longer once rolled into a cigarette, etc.
Once marijuana is produced on a larger scale those chemicals will enter the production chain. Just you watch. Already pot is loaded with chemicals from the fertilizers used by growers, but that's small potatoes to what will happen once industry takes over and moves to ensure their products are equal in every way from coast to coast.
There really aren't many additives. A lot of the most harmful substances in tobacco smoke (fromaldehyde, hydrogen cyanide, tar, arsenic, cadmium) are what is produced by buring the tobacco plant.
Just don't light stuff on fire and breath in the fumes/smoke.
Edit: I shouldn't say there aren't many. There a quite a few. I'm trying to emphasize most of the damage comes from the plant, not the additives.
Edited by Mattjvd, 15 November 2017 - 12:06 PM.