1) Funding programs to educate people with factual information about the dangers of substance abuse to persuade as many people as possible that using drugs is probably not in their best interest and, in particular, to persuade some of the individuals who are most at risk of going down that path that maybe spending some time on the psychotherapist's couch dealing with the root causes of their problems would be a good idea
2) Funding programs for at risk people without health insurance to provide affordable access to mental health services so they can resolve their problems before they resort to the dysfunctional strategy of using mood-altering substances to cope
3) Funding treatment for the addicts who want to get off drugs to successfully do so
Right now, 0% of the money that an addict spends on purchasing drugs goes towards anything positive. 100% goes straight into the pockets of the drug cartels and their middlemen with no social benefit whatsoever. What I'm saying is that you could lower the price of the drug just enough to make the profit-to-risk ratio unattractive to the cartels (and reduce the likelihood that a crackhead is going to have to burglarize your house in order to fund his drug habit) and simultaneously bring in enough tax revenue to fund programs aimed both at reducing the demand for drugs and reducing the societal impact of the problem by improving public mental health and providing treatment for addicts.