Are you sure? From the State Department website:
The GOS[Government of Singapore] nonetheless is concerned about the increase in addiction rates and recidivism among drug offenders who have undergone treatment. There are currently about 9,000 addicts undergoing rehabilitation in Singapore treatment centers, the same number as in 1995.
Figures for the Netherlands--
Demand Reduction. The Netherlands has extensive demand reduction programs and lowthreshold medical services for addicts, who are also offered drug rehabilitation programs. Authorities believe such programs reach about 7080 percent of the country's 25,000 harddrug users (in a total population of 15.1 million).
http://www.state.gov/www/global/narcotics_law/1996_narc_report/index.html
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Using a figure of 3 million for Singapore in 1996, that works out to an addiction rate of about 0.30%. Using the State Dept. figures for the Netherlands, the addiction rate was about 0.17%.
For comparison, here are the latest govt. figures I could find for the US:
"There were an estimated 980,000 hardcore heroin addicts in the United States in 1999, 50 percent more than the estimated 630,000 hardcore addicts in 1992." [that's a 0.35% rate in a population of 280,000,000]
--www.usdoj.gov/ndic/pubs07/794/heroin.htm
I'll do some homework and get back to you.