Members of the UK Independent Scientific Committee on Drugs undertook a multicriteria decision modelling analysis to analyse harms associated with various different drugs and substances.[1] In total, 20 drugs were scored on 16 different harms criteria.[1] The modelling suggested that heroin, crack cocaine, and methamphetamine were the most harmful drugs to individuals, and that alcohol, heroin, and crack cocaine were the most harmful to others.[1]

Reference:
[1] Nutt DJ, King LA, Phillips LD; Independent Scientific Committee on Drugs. Drug harms in the UK: a multicriteria decision analysis. Lancet 2010; 376 (9752): 1558–1565.