An international team of researchers from Australia and the United States assessed the global prevalence of illicit drug use and quantified its adverse effects on health, as measured in years of life lived with disability (YLDs), years of life lost (YLLs), and disability-adjusted life years (DALYs).
Investigators reported that more people were likely to be dependent on opioids and amphetamines than on other controlled substances, and that overall, illicit drug use was responsible for 0.9 percent of DALYs worldwide. (Tobacco smoking was estimated to cause 6.3 percent of DALYs worldwide; alcohol was estimated to cause 3.9 percent.) By contrast, researchers reported that "regular cannabis use made a very small contribution to disease burden through its contribution as a risk factor for schizophrenia" - a link which was acknowledged to be "controversial" in an accompany commentary since existing research on the plant's potential association with the disease is not yet definitive.
In total, researchers estimated that 13.1 million people globally are dependent on cannabis, including 1.8 million people in North America. Investigators estimated 15.5 million people worldwide were dependent on opioid drugs and 17.2 million were dependent on amphetamines.
Full text of the study, "Global burden of disease attributable to illicit drug use and dependence: findings from the Global Burden of Disease Study 2010," appears in The Lancet.