Not sure if this discussion is still going on, but thankfully as a university student I get free access to academic papers.
https://mega.nz/#!Wxh1nQYQ!48kvvUvLn7NSoDFReE0wj3SSS_NP0 2fpVxk4f2aFq4EThis is a paper from 2013 of around 50,000 people and assessed the dangers associated with use of marijuana and lung cancer.
"At the baseline conscription assessment, 10.5% (n=5,156) reported lifetime use of marijuana and 1.7% (n=831) indicated lifetime use of more than 50 times, designated as ‘‘heavy’’ use. Cox regression brown townyses (n=44,284) found that such ‘‘heavy’’ cannabis smoking was significantly associated with more than a twofold risk (hazard ratio 2.12, 95 % CI 1.08–4.14) of developing lung cancer over the 40-year follow-up period, even after statistical adjustment for baseline tobacco use, alcohol use, respiratory conditions, and socioeconomic status."
So basically, it's not nearly as bad as cigarettes but it's still going to give you an increased chance of lung cancer.