Like tobacco smoke, marijuana smoke contains cancer-causing chemicals. There are 33 cancer-causing chemicals contained in marijuana. Marijuana smoke also deposits tar into the lungs. In fact, when equal amounts of marijuana and tobacco are smoked, marijuana deposits four times as much tar into the lungs. This is because marijuana joints are un-filtered and often more deeply inhaled than cigarettes.

A somewhat misleading infographic concerning the amount of tar deposited in smokers' lungs by marijuana is frequently shared on social media sites:
https://www.snopes.com/uploads/image...natarphoto.jpg

However, although it may be true that marijuana smoke deposits more tar into a smoker's lungs than tobacco smoke, the above-displayed photograph does not accurately depict the difference in overall harm caused to a tobacco smoker's lungs versus a marijuana smoker's lungs. Marijuana contains many of the same cancer-causing chemicals as tobacco smoke, but a recent study found no link between marijuana and an increased risk of lung cancer. According to Dr. Hal Morgenstern, a University of Michigan epidemiologist, this factor was likely attributable to the differences between marijuana and tobacco use:

When you think about people smoking 20 to 40 cigarettes a day for 40 years, they're smoking hundreds of thousands of cigarettes. The exposure that marijuana users get is more than a magnitude of difference less.

However, a study funded by the National Institute on Drug Abuse found that even heavy marijuana smokers did not have an increased risk of developing lung cancer:

We hypothesized that there would be a positive association between marijuana use and lung cancer, and that the association would be more positive with heavier use. What we found instead was no association at all, and even a suggestion of some protective effect.

https://www.snopes.com/fact-check/ci...marijuana-tar/

Mixed messages
The Consortium collated the data from six different studies in four countries all over the globe, and all six suggested that marijuana use does not lead to lung cancer, which was far from the results the scientists expected.

Some experts believe it’s due to the rate of consumption. Yes, marijuana deposits more tar into your lungs per gram than cigarettes, but cigarettes tend to be smoked more habitually and in higher quantities. Few people are smoking the equivalent of a pack a day in marijuana.


https://www.benzinga.com/markets/can...d-and-cancer-1