I always take issue with that kind of cause-and-effect relationship. I mean, yeah, someone takes drugs and then they commit suicide, okay. But the types of personalities who will take (and abuse) drugs are the same personality types who are more prone to suicide anyway, which is WHY they're taking drugs in the first place. Because their coping skills at life are lacking (sez me). So how much do the drugs themselves have to do with it? Not necessarily much at all, if that makes any sense.
In other words, is banning drugs going to reduce the suicide rate? Methinks not.