Public Health Impact of Marijuana Compared With Other Drugs

"The public health burden of cannabis use is probably modest compared with that of alcohol, tobacco, and other illicit drugs. A recent Australian study96 estimated that cannabis use caused 0·2% of total disease burden in Australia—a country with one of the highest reported rates of cannabis use. Cannabis accounted for 10% of the burden attributable to all illicit drugs (including heroin, cocaine, and amphetamines). It also accounted for around 10% of the proportion of disease burden attributed to alcohol (2·3%), but only 2·5% of that attributable to tobacco (7·8%)."

Source: 

Hall W, Degenhardt L. Adverse health effects of non-medical cannabis use. Lancet. 2009 Oct 17;374(9698):1383-91. doi: 10.1016/S0140-6736(09)61037-0. PMID: 19837255.