I did for a few years until I realized the futility of trying to convince drug addicts that not being on drugs was good for them.
Unfortunately, the reality is that most drug addicts prefer to be high, and the more they use, the stronger that preference. Worse, an aspect of many mental illnesses (especially the schizoid series) is paranoia regarding medication, so while ill most of the mentally ill will refuse their medications, though they may otherwise want to take their meds when not ill. (This is why stable housing is so important for the mentally ill: missing even a single dose can cause the illness to relapse, leading the individual to actively avoid medication.)
Unless you also volunteer to help the homeless on weekends.