There is a kind of drug called "SSRIs" - which stands for Selective Serotonin Reuptake Inhibitors. These are drugs such as Prozac, Paxil and Zoloft that are supposed to regulate the amount of a neurological chemical made naturally in the body called "Seritonin". Basically the seritonin is there as a neurotransmitter. It allows a message to get to one nerve to the other. When the receiving nerve gets the message, it's called "reuptake". So, these drugs stop "reuptake" from occurring, thereby making more seritonin available in the brain and also cutting off the communication abilities of the brain.
I read somewhere that in experiments with rats, these "SSRIs" made the rats get insanely violent and that too much seritonin will do that to any animal, no matter how tame it is. I will post where I got this from once I figure out what book it was.
Some of the side effects of Selective Serotonin Reuptake Inhibitors are agitation, nervousness, sexual problems, nausea, fever, kidney problems, heart problems, liver failure and suicide.
Here's a Fox News investigation into SSRIs and other psychiatric drugs: