In the case of cocaine, there is an even more striking precedent for evidence being ignored: during the early 1990s the World Health Organisation conducted what is probably the largest ever study of global cocaine use. In March 1995 they released a briefing kit which summarised their conclusions, with some tantalising bullet points.
"Health problems from the use of legal substances, particularly alcohol and tobacco, are greater than health problems from cocaine use," they said. "Few experts describe cocaine as invariably harmful to health. Cocaine-related problems are widely perceived to be more common and more severe for intensive, high-dosage users and very rare and much less severe for occasional, low-dosage users."
The full report - which has never been published - went on to challenge several of the key principles driving prohibition, and was extremely critical of most US policies. It suggested that supply reduction and law enforcement strategies have failed, and that alternative strategies such as decriminalisation might be explored, flagging up such programmes in Australia, Bolivia, Canada and Colombia.
"Current national and local approaches which over-emphasize punitive drug control measures may actually contribute to the development of heath-related problems," it said, before committing heresy by recommending research into the unintended adverse consequences of prohibition, and discussing "harm reduction" strategies. "An increase in the adoption of more humane, compassionate responses such as education, treatment and rehabilitation programmes," it said, "is seen as a desirable counterbalance to the overreliance on law enforcement measures."
It specifically singled out anti-drug adverts which sought to modify behaviour through fear. "Despite a broad range of educational and prevention approaches, most programmes do not prevent myths, but perpetuate stereotypes and misinform the general public. Such programmes rely on sensationalized, exaggerated statements about cocaine which misinform about patterns of use, stigmatize users, and destroy the educator's credibility. This has given most education campaigns a naïve image and has reduced confidence in the quality and accuracy of these campaigns."