This documentary is based on a study by Professor David Nutt, a psycho-pharmacologist at Bristol University and member of the Advisory Council on Misuse of Drugs, published early 2007. He and his team analyzed the evidence of harm caused by 20 drugs. They asked a group of 29 consultant psychiatrists who specialize in addiction to rate the drugs in categories related to physical harm, related to the likelihood of addiction and related to social harms. They also extended the analysis to another group of 16 experts spanning several fields including pharmacology, police, chemistry, forensics, psychiatry and legal services. The ranking: 20 Cathinone (Khat) 19 Amyl nitrite (Poppers) 18 MDMA/ Ecstasy 17 GHB 16 Anabolic steroid 15 Methylphenidate (e.g. Ritalin) 14 LSD/ Acid 13 4-MTA 12 Solvents 11 THC (Cannabis) 10 Buprenophine hydrochloride 9 Nicotine (Tobacco) 8 Amphetamine/ Speed 7 Benzodiazepine (e.g. Valium) 6 Ketamine 5 Alcohol 4 Methadone 3 Barbiturates 2 Cocaine/ Crack cocaine 1 Heroin