One Dutch study has compared cannabis use in San Francisco, where it is illegal, with Amsterdam, where it is illegal but de-penalised: 62 percent of those surveyed in San Francisco reported having used it at one time or another as compared with 34.5 per cent in Amsterdam.
P.Cohen and H Kaal, ‘
The irrelevance of drug policy: patterns and careers of experienced cannabis use in the populations of Amsterdam, San Francisco and Bremen’, CEDRO 2001.
A more recent European study found that 15.8 per cent of young men in Britain were reported to be using cannabis at least once a month, as compared with 9.7 per cent in the Netherlands. EMCDDA Statistics 2005,
http://stats05.emcdda.europa.eu/en/elements/gpstab08a-en.html