Decriminalization and Use Rates
"The available evidence suggests that removal of the prohibition against possession itself (decriminalization) does not increase cannabis use. In addition to the Dutch experience from 1976 to 1983, we have similar findings from analysis of weaker decriminalization (with fines retained for the offense of simple possession of small quantities) in 12 US states (Single, 1989) and South Australia and the Australian Capital Territory (Hall, 1997; McGeorge & Aitken, 1997). The fact that Italy and Spain, which have decriminalized possession for all psychoactive drugs, have marijuana use rates comparable to those of neighboring countries provides further support."
MacCoun, Robert and Reuter, Peter, "Evaluating alternative cannabis regimes," British Journal of Psychiatry (London, United Kingdom: American Royal College of Psychiatrists, February, 2001) Vol. 178, p. 127.