Marijuana is the most used illegal drug worldwide but painkiller addiction kills more people Prescription painkillers caused more than half of the estimated 780,000 worldwide drug-related deaths in 2010 A study by the University of Washington found that drug users most likely to use substance produced close to home Marijuana is the most used illegal drug worldwide but addiction to legal painkillers kills the most people, according to new research. Scientists found that cannabis was used more than cocaine and heroine in the first ever study of world-wide drug use. But experts from the University of Washington found that opioid painkillers such as vicodin, oxycontin and codeine caused more than half of the estimated 78,000 drug-related deaths worldwide. Study: Scientists have found that marijuana topped the list of most used illicit drugs worldwide, but prescription painkillers accounted for more than half of the estimated 780,000 drug-related deaths around the globe in 2010 The study, which did not include data on ecstasy and hallucinogens, also found that men in their 20s are most likely to abuse drugs, with the highest rates of abuse found in Australia, the UK, Russia and the U.S. The research, which was published in The Lancet, found that the rate of drug-related deaths in countries that take a hard-line against illicit substance abuse was much higher than in states where the policy is to wean people off drugs by using methadone clinics and needle exchange programmes. Theo Vos, from the university's Institute for Health Metrics and Evaluation and senior author of the study, said that although his team had few concrete numbers and had to rely on modeling techniques, the results still prove that there are drug problems in most parts of the world. Professor Vos added that people tended to abuse drugs produced close to home: cocaine in North America, amphetamines and opioids in Asia and Australia. The lowest rates of drug abuse were in Asia and Africa. New problem: Researchers warned that prescription drug abuse has only been a problem in the U.S for the past decade Abuse: While cannabis is the most popular illegal drug used, the study found that people are more likely to use drugs made closer to home, for instance people in North America are more likely to abuse cocaine (file picture) Michael Lysnkey, of the National Addiction Centre at King's College London, who co-authored an accompanying commentary warned that prescription drug abuse in the U.S only appears to have become problematic in the last decade and warned that health officials will need to address the issue. He said: 'It's possible in another 20 years, patterns will again change in ways we can't predict.' In a related study, scientists also found that mental health and drug abuse problems including depression, schizophrenia and cocaine addiction kill more people worldwide than AIDS, tuberculosis, diabetes or road accidents. In some developing countries such as India, attempts to stop AIDS have slowed drug abuse as they focus on helping people kick their addictions, according to Vikram Patel, of the Centre for Global Mental Health at the London School of Hygiene and Tropical Medicine. Worrying: A separate study found that mental health and drug abuse problems including depression, schizophrenia and cocaine addiction kill more people worldwide than AIDS, tuberculosis, diabetes or road accidents He recommended an approach to drug use similar to current controls on tobacco. He said: 'A decriminalized drug policy could potentially transform the public health approach to drug use. The enormous savings in the criminal justice system could be used to fund addiction treatment programs. The results of the study were published as the the U.S Government confirmed that it will not sue the states of Colorado and Washington to stop them from legalising marijuana. Instead of trying to reverse the legalisation following a vote in November, the justice department said that it will try and focus on stopping underage access to the drug and keeping drug cash from criminals. As well as the two states which legalised the drug asap, 20 other states allow the drug to be used for medicinal purposes. Marijuana is still banned by federal law.