Alcohol is nearly as harmful as heroin and tobacco is more dangerous than cannabis, LSD or ecstasy, according to a new classification table of drugs published in a medical journal Friday.
The table, published in The Lancet, was drawn up by a group of leading British scientists and ranked heroin, cocaine, barbiturates and street methadone as the most harmful drugs, closely followed by alcohol in fifth place.
Tobacco was assessed to be the ninth most dangerous drug behind ketamine -- commonly used as a horse tranquilizer -- benzodiazepines, which are prescription tranquillisers, and amphetamines.
Cannabis was said to be the 11th most harmful. LSD was ranked 14th and so-called "clubbers' drug" ecstasy in 18th, or third last, place.
The classifications were based on individual drugs' so-called "harm scores" -- the physical damage to the user; how likely the drug was to induce dependency; and the effect of its use on families, communities and society.
Each of the three categories was split into nine categories of risk and independent experts including psychiatrists, chemists and forensic scientists ranked each category on a scale from 0 ("no risk") to 3 ("extreme risk").
Heroin scored 2.7 on the harm scale with alcohol just under 2. Tobacco scored 1.7 and ecstasy scored just over 1.1.
One of the scientists, Professor Colin Blakemore, the chief executive of the government-funded public health body the Medical Research Council, said their findings differed markedly from the existing drugs classification in Britain.
"Alcohol and tobacco are way up there in the league table, with alcohol being not very far behind demonised terrors of the street like heroin," he said.
His colleague, Professor David Nutt, from the University of Bristol, western England, said isolated cases of unpleasant and unpredictable responses to drugs were allowed to dictate policy.
"A more scientific view is that these risks have to be assessed against their effect on the whole population," he added.
Possessing Class A drugs like heroin, cocaine and crack, ecstasy and LSD currently carries a maximum seven-year prison sentence; cannabis is a Class C drug, while alcohol and tobacco are unclassified.
Blakemore said he hoped policy makers would "take note" that their table differed substantially from the official classification, which a separate British study published on March 8 also criticised as inadequate.
The RSA Commission on Illegal Drugs, Communities and Public Policy said Britain's drug laws should be replaced by a system recognising the harm to health of substances like alcohol and tobacco rather than crime prevention.