ABSTRACT
While it is generally accepted that drug use can have serious consequences for health and social well being, establishing a causal relationship between substance use and ill-health is problematic. As pointed out with regard to attributing causation between alcohol use and alcohol related problems: ‘Causality here is not a matter of Newtonian physics, and uncertainty is part of every equation’ (Edwards et al., 1994). The uncertainty in attributing causation is all the greater with substances other than alcohol and tobacco. Users of illicit drugs seldom use only one drug exclusively. Heroin users in some countries, for example, will often use benzodiazepines. In many countries the majority of illicit drug users also use tobacco. Attributing causality to the use of a particular drug is therefore difficult.
