Given the increased risk of chronic obstructive pulmonary disease (COPD) among smokers of tobacco, there is concern that a similar risk may exist among smokers of marijuana. A limited body of evidence suggests an association between regular marijuana smoking and adverse effects on respiratory health. Studies that address this possibility have many limitations, however. The finding by Tan and colleagues that smoking both marijuana and tobacco is associated with a greater risk of COPD than smoking only tobacco suggests an additive effect of the 2 substances on lung health. This study involved an older population that is more at risk of COPD. Marijuana smoking by itself probably does not lead to COPD
