Back in 2010, former government drug czar David Nutt released the findings of a study which revealed alcohol to be the most dangerous drug based on harm caused to users and harm caused to others.
For the study, members of the British Independent Scientific Committee on Drugs was asked to rate 20 drugs on 16 criteria such as drug-specific damage, mortality, dependence and international damage. Drugs were scored on a 100-point scale. Here is a display of the weighted scores:
Alcohol was found to have scored the highest (72) on the rating system. It was followed by heroin (55),
crack (54), crystal meth (33) cocaine (27), tobacco (26),
amphetamine/speed (23), cannabis (20), GHB (18), benzodiazepines (15),
ketamine (15), methadone (13), butane (10), qat (9), ecstasy (9),
anabolic steroids (9), LSD (7), buprenorphine (6) and magic mushrooms
(5). Again, that's 3.6 times as dangerous as pot.
These findings, published in the lancet, back up claims that got Nutt fired about the hypocrisy of certain drug laws. According to the Guardian, Nutt believes that research into mental illness is being hampered by the prohibition of drugs such as psilocybin and LSD.