Marijuana has topped the list of the most popular drug used world-wide, defeating cocaine, heroin, methamphetamine, hallucinogens and other drugs in a first-of-its-kind global survey of illegal drug abuse by the Institute for Health Metrics and Evaluation at the University of Washington.

Marijuana was also considered to be the least lethal illicit drug.

The Institute also found that addictions to popular doctor-prescribed painkillers like Vicodin, Oxycontin and codeine proved fatal in a majority of the people. Out of the nearly 78,000 worldwide drug-related deaths in 2010, more than half of them were caused by pain pill addictions.

Overall, among the drugs examined, 20-year-olds were found to be frequent drug abusers. Worst affected countries were Australia, Britain, Russia and the lowest rates of drug abuse were recorded in Asia and Africa.

The study was published online, Thursday in the journal, Lancet.

"Even if it is not very solid data, we can say definitely that there are drug problems in most parts of the world," said Theo Vos, of the Institute for Health Metrics and Evaluation at the University of Washington, the study's senior author.

Vos said that people get addicted to drugs that are produced locally - cocaine in North America, and amphetamines and opioids in Asia and Australia.

Other experts urged officials across the globe to introduce drug reforms and measures to prevent and address possible health problems from drug abuse.

"The illicit use of prescribed opiates in the U.S. has only happened in the last 10 years or so," said Michael Lysnkey, of the National Addiction Centre at King's College London, who co-authored an accompanying commentary. "It's possible in another 20 years, patterns will again change in ways we can't predict."