Senior author Theo Voss of the Institute for Health Metrics and Evaluation at the University of Washington in Seattle and colleagues said marijuana beat cocaine, heroin, methamphetamine and hallucinogens when it comes to prevalence of users.
The researchers said the United States, Britain, Russia and Australia had the highest burden of drug abuse.
The study, published online in the journal The Lancet, showed more than half of the estimated 78,000 deaths worldwide from drugs in 2010 were caused by pills for relieving pain.
Worldwide, more people were dependent on opioids and amphetamines than other drugs.
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