The study, one of the most exhaustive of its kind, suggests that the classic three-tier definition of drugs - hard, soft and legal - should be overturned.
A team, led by Professor Bernard-Pierre Roques, one of France's leading authorities on narcotics, classified all drugs, legal and illegal, according to five possible ill-effects: physical dependency, psychological dependency, damage to the brain, damage to the body and damage to society. Alcohol scores as very high risk in the first two categories and high risk in the other three. Cannabis is graded as a low risk, very low risk or no risk in all categories. The most dangerous single drug is heroin, partly because of the dangers associated with the way it is taken. Tobacco should be in the next level of risk, alongside ecstasy and LSD.
The report, commissioned by the French Health Minister, Bernard Kouchner, will inflame the debate within the government on the legalisation, or decriminalisation, of cannabis.