Sigh. Yet another one-size-fits-all, "master-molecule" explanation (and a literal molecule this time... how nice) for actions carried out by complex human beings, each of whom is unique.
It's been known for some time that giving these drugs to adolescents or young adults can increase the risk for suicide or other violence. And, yes, they are overprescribed -- sometimes just as a way of controlling unwanted behavior. But -- ADHD is a real illness, and is treatable by these same drugs; depression is a real illness, and is treatable by antidepressants -- and in both cases, the treatment must be closely supervised by professionals who know what they're doing and are able to augment the drugs with other forms of treatment.
Here's a scenario: take an adolescent male who's seriously depressed, hostile, unable to function, no friends, poor schoolwork -- miserable and headed downhill, in other words. Now add a health system that's geared to short-term results of the kind that can be achieved with drug treatment, without other, long-term therapies that are typically needed to deal with major depression, and which many insurance companies don't cover. (Assuming the kid is insured at all.)
So he's on meds, and they start working. But his depression was caused by more than just brain chemistry -- he feels inadequate relative to parental expectations, or he may have been abused at home, or feel like an outcast at school -- whatever. Now he has more energy, but his problems haven't gone away.
This is an adolescent male we're talking about, remember? Raging hormones, poor impulse control, brain development not yet complete... Is it that surprising that every so often one of these kids acts out whatever he's thought about while depressed, now that he's sufficiently activated by the meds? Most likely suicide, but maybe revenge on a world that doesn't understand him?
It's not useful to look for a single cause for these events. I've seen statements to the effect that young shooters are always on one or other of these drugs, but I've yet to see anything other than anecdotal evidence for such a sweeping generalization. And even if it turns out to be true, it's worth remembering that the drugs were prescribed for a reason, whether good or bad -- whether the patient is seen as having problems or as being a problem.
It's also worth remembering that most violence is less dramatic than these mass shootings... if we want a safer society, we need to look at violence, and its multiple causes, as a whole, rather than focusing on a tiny but spectacular fraction of the homicides that take place every week in this country.
I also find it curious, perhaps ironic, that folks on both sides of this debate turn so readily to explanation-by-commodity, putting the blame on products (guns or drugs) that are widely used in large part because they're heavily marketed by the corporations that profit from their sale. I don't know what this means, except as a symptom of what a consumer-oriented society this has become -- but I find it interesting.