If people didn't take illicit drugs then the whole drug "scene" with all its associated issues would disappear. Hence we have to ask, why do people take these illicit drugs in the first place? I am no expert but it seems to me there are three types of drug user:

1. Those who dabble occasionally to get the "high" but that's it.
2. Folk from group 1 who go on to become physically addicted (do all folk from group 1 inevitably end up in group 2, I don't know?)
3. Those who take them in order to slip into oblivion to escape the hopelessness of their situation.

I don't have any sympathy for Group 1 as the risks are very well known now, so there is no excuse (akin to smoking). So eliminating Group 1 would eliminate Group 2. Group 3 folk are in a different category and the only way here is to help them get back on their feet and improve their worth/self-esteem. Sounds simple but as there may be a myriad of factors at play, not easy.