Several approaches.
There is contingency management / motivational interviewing, but bribery is probably a better way to describe it. You just ask what the person wants, what is good/desired and produce benefit from the medications. This presupposes that the medications actually have a benefit. If that cannot be objectively shown, then that is the problem and not the person. And if the medicaitons do help then either show that goals of getting a job, money, stuff is furthered by the medications, or at least possibly so enough to show a reason to try them. Alternatively, if the medicines work, then instituting a payment system for showing up and taking them.

Alternatively, the way you train a dog with behavior problems is putting them in a group of well-behaved animals. This is called residential treatment facility. It also works for 12 step programs with sponsors, cults, army barracks, religious retreats, Asian re education camps....any of which could be used instead of residential treatment facilities for the same purpose; it's mainly a case of which works better for the individual.