Marijuana is probably going to give you cancer
The BLF report contradicts a study from earlier this year claiming that marijuana does not cause lung damage. Back in January of 2012, Stefan Kertesz, an associate professor in the UAB Division of Preventive Medicine, published a study claiming that occasional marijuana use was associated with increases in lung air flow rates and increases in lung capacity. His data showed that even up to moderately high-use levels — one joint a day for seven years — will not decrease air-flow rates or lung volumes.
The Kertesz study did not make mention of marijuana as a potential carcinogen.
What makes marijuana particularly dangerous, say BLF researchers, is the way that it is smoked. Cigarette users quickly exhale their smoke, whereas cannabis users tend to hold it in for as long as possible to better absorb its THC content. It's this practice of holding smoke in the lungs that significantly exacerbates its carcinogenic effects.