if i was president of new zealand *pfffft, lol* i wouldn't just say 'okay everyone, drugs are legal - go nuts'. i would introduce it over a ten year period. i would borrow to massively invest in education and infrastructure then:
1) legalise weed. available only from licensed dealers, such as coffee shops and bottle stores. very strictly regulated, with massive fines for selling to under 18s. cheap, easy access to weed would break the link between buyers and dealers who often push harder drugs on their weed-buying customers. reduced demand for heavier drugs would become apparent. reduced property crimes.
2) 2-3 years later, legalise pharmeceutical grade g, ecstasy and psychotropics. available only from chemists. again, massive fines for selling to underage punters. again, breaking the links between everyday users and hard core dealers. demand for speed, coke etc reduced (when you have access to a cheap booze, weed, e and lsd buzzes, not many would be bothered dealing with dealers). massive reduction in property crimes.
3) in year 5-6, legalise speed, cocaine and heroin, available only on prescription from specialist clinics. buyers must return every month for health and welfare checkups.
4) after ten years, allow commercial production of branded drinks, foods, supplements etc containing strictly regulated amounts of various drugs. coca cola could once again become the real thing.
yes there would be increased consumption of drugs for the first few years and there would be social costs, but people learn and self regulate and even when they do go down the toilet, they have expert help readily available, paid for by a massive increase in tax revenues and reduction in crime. drug taking would also be qualitatively incomparable, with safe, clean drugs available with proper dosage instructions (and perhaps sold complete with OD antidote drugs). tourism would have to be managed, maybe with organised drug taking districts as in amsterdam. the bottom line is this - prohibition is stupid, it does not, and will not ever work. radical solutions are called for.