Vapor is efficient. A study from ucla looked at what the most efficient and in theory safest delivery mechanism for thc, the active paychodelic chemical in marijuana, is. It compared water bong, joint cigarette, pipe, and vaporizer. They calculated the amt of thc compared to contaminants and pollutants. Vapor then joint then pipe then water bong. This doesn't mean it's safe just requires least amt for fx.
YES. Recent studies have found links of lung cancer to smoking marijuana. Marijuana is a risk factor. Its impact is dependent on intensity of exposure and duration. The best information to date is that it is a carcinogen linked to developing lung cancer. Emphysema changes are demonstrated in lung tissue of mj smokers. However, limited specific data based on impact legal status has on mj studies.