The highly carcinogenic effects of nicotine and other compounds contained in cigarettes and other tobacco-related products are well recognized (92). Perhaps less well appreciated is the fact that smoked cannabis can contain more tar and polycyclic aromatic hydrocarbons than smoked tobacco (93). While its link to lung cancer is tenuous (66;94), cannabis smoking has been linked to chronic bronchitis and there is growing evidence for cannabis-related impairment of respiratory function (95). A cannabis joint can produce as much airflow obstruction as 2.5-6 tobacco cigarettes (96) and multiple population studies support the adverse respiratory effects of cannabis (97-100). Taylor and colleagues (99) found that even after adjustment for tobacco use, respiratory symptoms in young adult cannabis dependent subjects exceeded those observed in tobacco smokers smoking 1-10 cigarettes/day. Cannabis-dependent individuals experience wheezing, exercise-related shortness of breath, nocturnal wakening with chest tightness, morning sputum, coughing, chest sounds and phlegm production (100). Individuals who use both cannabis and tobacco have a markedly elevated risk of respiratory distress, compared with cannabis use or tobacco use alone (99;101). For instance, Moore and colleagues (100) found that
