Heavy habitual marijuana smoking does not cause an accelerated decline in FEV1 with age.

To assess the possible role of daily smoking of marijuana in the development of chronic obstructive pulmonary disease (COPD), we evaluated the effect of habitual use of marijuana with or without tobacco on the age-related change in lung function (measured as FEV1) in comparison with the effect of nonsmoking and regular tobacco smoking. A convenience sample of 394 healthy young Caucasian adults (68% men; age: 33 +/- 6 yr; mean +/- SD) including, at study entry, 131 heavy, habitual smokers of marijuana alone, 112 smokers of marijuana plus tobacco, 65 regular smokers of tobacco alone, and 86 nonsmokers of either substance were recruited from the greater Los Angeles community. FEV1 was measured in all 394 participants at study entry and in 255 subjects (65 %) on up to six additional occasions at intervals of > or = 1 yr (1.7 +/- 1.1 yr) over a period of 8 yr. Random-effects models were used to estimate mean rates of decline in FEV1 and to compare these rates between smoking groups. Although men showed a significant effect of tobacco on FEV1 decline (p < 0.05), in neither men nor women was marijuana smoking associated with greater declines in FEV1 than was nonsmoking, nor was an additive effect of marijuana and tobacco noted, or a significant relationship found between the number of marijuana cigarettes smoked per day and the rate of decline in FEV1. We conclude that regular tobacco, but not marijuana, smoking is associated with greater annual rates of decline in lung function than is nonsmoking. These findings do not support an association between regular marijuana smoking and chronic COPD but do not exclude the possibility of other adverse respiratory effects.