The research, conducted by Professor David Nutt of Britain's Bristol University and his colleagues, proposes that a new framework be created for the classification of harmful substances, based on the actual risks posed to society. The study ranks alcohol and tobacco among the ten most dangerous substances.

The Bristol University researchers used three factors to determine the harm associated with any drug, including physical harm to the user, the drug's potential for addiction, and the impact on society of drug use.

The researchers asked two groups of experts - psychiatrists specializing in addiction and legal drugs, and police officials with scientific or medical expertise - to assign scores to twenty different drugs, including heroin, cocaine, ecstasy, amphetamines and LSD. Nutt and his colleagues then calculated the overall rankings. The experts ended up agreeing with each other - but not with the current British dangerous substances classifications.

While heroin and cocaine were ranked most dangerous, followed by barbiturates and street methadone, alcohol made the list as the fifth most harmful drug and tobacco as the ninth most harmful. Marijuana came in 11th, and ecstasy came in nearly last.

Yet, according to existing British and U.S. drug policies, alcohol and tobacco are legal, while marijuana and ecstasy are both illegal. Previous studies, including one from a British parliamentary committee in 2006, have questioned the scientific rationale for Britain's drug classification system.

Tobacco causes 40 percent of all hospital illnesses, while alcohol is blamed for more than half of all visits to hospital emergency rooms. The substances also harm society in other ways, damaging families and occupying police services.

The researchers hope that the study will provoke debate within the UK and beyond about how drugs - including socially acceptable drugs such as alcohol - should be regulated. While different countries use different markers to classify dangerous drugs, none uses a system like the one proposed by the Bristol University study, which could serve as a framework for international authorities.

Other experts in the field not connected to the research feel that this study is the first real step towards an evidence-based classification of drugs and that, based on the paper's results, alcohol and tobacco could not reasonably be excluded.

While experts agreed that criminalizing alcohol and tobacco would be challenging, they said that governments should review the penalties imposed for drug abuse and try to make them more reflective of the actual risks and damages involved. The study called for more education so that people were aware of the risks of various drugs.