Marijuana does not impair lung function—at least not in the doses inhaled by the majority of users, according to the largest and longest study ever to consider the issue, which was published today in the Journal of the American Medical Association.
Researchers working on a long-term study of risk factors for cardiovascular disease (the Coronary Artery Risk Development in Young Adults or CARDIA study) tested the lung function of 5115 young adults over the course of 20 years, starting in 1985 when they were aged 18 to 30.
They found that marijuana use was almost as common as cigarette smoking in the sample, which was designed to reflect the U.S. population. Among participants, the average marijuana user toked 2-3 times a month, while the average tobacco user smoked eight cigarettes a day. Those who smoked both tended to do so slightly more frequently than those who smoked only cigarettes or only marijuana.