Singapore is somewhat unique in that it's a country with very restricted freedoms, which have been given up in exchange for security/safety. It's extraordinarily rule-bound, and, in many ways, is the antithesis of the United States, in which freedoms reign. In such a structured, government controlled and monitored society, all sorts of rules can be laid down, and enforced through strict punishment. I wouldn't try and use it as a model for other countries.

But - hey, might be worth executing anybody who uses drugs to see what happens. But I hope you're going to start with the really destructive ones, like Alcohol and Nicotine before you start looking at the less harmful ones such as cannabis.