Shannon,

Thanks for your question.  There are two areas that I would like to address in order to answer your question.  The first is the effect of marijuana on the lungs.  Long term use of marijuana (cannabis) causes chronic irritation of the airways, along with chronic mucus and sputum production.  There is also an effect on the small to medium sized airways, similar to tobacco smokers and, over time, the damage to lung tissue can cause chronic lung disease.  I have not been able to find an association between smoking marijuana and lung cancer.

The other area to discuss is the addictive potential of smoking cannabis.  Most young people consider marijuana a "soft drug" with little addictive potential.  Studies have shown that some people, especially teens, have a greater chance of addiction to marijuana.  Many people feel that smoking marijuana can lead to use of more powerful, addictive drugs, but this is more behavioral than cannabis related.  The bottom line is that marijuana in some individuals can be addictive, and associated with behavior changes that can interfere with daily activities including school, work, and social behavior. 

I hope this has been helpful.

Martin Cane, M.D.