British experts evaluated substances including alcohol, cocaine, heroin, ecstasy and marijuana, ranking them based on how destructive they are to the individual who takes them and to society as a whole.
Researchers analyzed how addictive a drug is and how it harms the human body, in addition to other criteria like environmental damage caused by the drug, its role in breaking up families and its economic costs, such as health care, social services, and prison.
Heroin, crack cocaine and methamphetamine, or crystal meth, were the most lethal to individuals. When considering their wider social effects, alcohol, heroin and crack cocaine were the deadliest. But overall, alcohol outranked all other substances, followed by heroin and crack cocaine. Marijuana, ecstasy and LSD scored far lower.
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The study was paid for by Britain's Centre for Crime and Justice Studies and was published online Monday in the medical journal, Lancet.
Experts said alcohol scored so high because it is so widely used and has devastating consequences not only for drinkers but for those around them.
"Just think about what happens (with alcohol) at every football game," said Wim van den Brink, a professor of psychiatry and addiction at the University of Amsterdam. He was not linked to the study and co-authored a commentary in the Lancet.
When drunk in excess, alcohol damages nearly all organ systems. It is also connected to higher death rates and is involved in a greater percentage of crime than most other drugs, including heroin.
But experts said it would be impractical and incorrect to outlaw alcohol.
"We cannot return to the days of prohibition," said Leslie King, an adviser to the European Monitoring Centre for Drugs and one of the study's authors. "Alcohol is too embedded in our culture and it won't go away."
King said countries should target problem drinkers, not the vast majority of people who indulge in a drink or two. He said governments should consider more education programs and raising the price of alcohol so it isn't as widely available.
Experts said the study should prompt countries to reconsider how they classify drugs. For example, last year in Britain, the government increased its penalties for the possession of marijuana. One of its senior advisers, David Nutt - the lead author on the Lancet study - was fired after he criticized the British decision.
"What governments decide is illegal is not always based on science," said van den Brink. He said considerations about revenue and taxation, like those garnered from the alcohol and tobacco industries, may influence decisions about which substances to regulate or outlaw.
"Drugs that are legal cause at least as much damage, if not more, than drugs that are illicit," he said.