Billybob, those types of cases are brought now and again, and I don't know of one that has won. Probably is one out there, but I'm not familiar with it.
Typically, Pharma cases (and I have a lot of them) deal with the side effects (to the patient). Although, this is against the doctors, I think to survive sj, you'd have to show that nutso was taken meds exactly as prescribed and docs knew or should have known the drugs were likely to cause some sort of violent psychotic break. A way uphill battle that would be expensive and require a lot of dueling experts.
A l
I'm sure it would be harder to prove a mental connection as opposed to a medical one, but there's been a growing body of info and cases ever since the first "Prozac defense". And it raises the question that if a drug is the cause of/excuse for violence in the context of criminal defense and there is data tying it to violent acts why would it not be a known side effect.
http://ssristories.com/index.php?p=won
And here's a recent, (though foreign) case,
Judge Agrees Prozac Made Teen A Killer
http://www.huffingtonpost.com/dr-peter-breggin/judge-agrees-prozac-made-_b_989536.html
Many of the school shootings have an SSRI,(antidepressants) connection,
http://ssristories.com/index.php?p=school