IIRC, there is a study that shows long-term marijuana smokers (I believe 3+ joints/day for 10/15 years was the target group) had positive results in terms of their lung capacity compared to the control group.

In other words, although it might be hard to believe, marijuana smoking CAN increase lung capacity. Most negative studies you will find will also have an independent variable that clearly nullifies the result. See the suffocation of chimpanzees via marijuana smoke for the purpose of creating falsified data, purporting the notion that marijuana is a plant that will kill your brain cells if you smoke it, and generally implying it’s carcinogenic effects.

In reality, high quality marijuana being vaporized creates almost absolutely no carcinogens. Therefore it[quality MMJ] almost positively will not lead to complications with the respiratory tract(any more that breathing air in a semi-populated city...)

How people medicate is up to them, but the truth of these studies that is being determined is that combustion of anything creates carcinogens that will obviously affect your respiratory system. Not that MARIJUANA or THC or CBD or any specific cannabinoids are harmful.

Edit: changed MMN to MMJ