@Pixie
"these costs would still apply if the drugs were legal, and perhaps would be more widespread, too. I can't see it would save money. And i would say lives are more important than money, anyway"
Not at all sure about that. Much of those trillions of dollars of costs to the public around the globe come from policing efforts, trying to control the drugs trade and then policing the drug -related crimes. A lot of the health costs associated with drug abuse could be ascribed, at least in part, to the fact that drugs are considered illegal so people will not seek medical help early enough; And because the drugs trade is illegal there are no quality controls over what goes into the drugs.
If you legalise the drug trade, regulate the manufacturing process, that offers greater security over the quality of the drugs themselves, and the exchequer get revenue from a trade that was formerly illegal and hence no tax no duty was paid, but now would be - and that revenue could offset costs of treatment etc.
There was a spate of cases of amputations in Glasgow back in the 1990s for instance, of heroin users, because the drug dealers there were cutting the heroin with all sorts of foreign additives, one of the most common being concrete dust which unfortunately lead to all sorts of serious health complications for IV drug users, as did the habit of sharing and reusing needles. All of these complications could be largely removed if the trade was legalised.