This article is very misleading and a good example of why a lot of these so called Public Health articles are BS. I work in this field, and I can tell you anecdotally at least (and we are talking thousands of cases I've reviewed) that although pot smokers don't seem to have an increased risk of lung cancer, they do seem to have very high rates of head and neck cancers. These cases usually involve men in their 40s-60s, and most of the ones I've seen also smoke tobacco. Also, epidemiologically speaking they do not have a method in the cancer case reporting programs to record whether or not a person smokes pot. We do collect tobacco and alcohol information, and in the military and VA hospitals Agent orange, Asbestos and Chemical Exposure information is collected as well. THERE IS NO ONE on a national, sustained basis collecting information on mariuuana smokers and cancer.
I can tell you what my significant other's experience has shown after treating thousands of drug addicts: Most of them started out using pot.
Horrible stuff!