i used to read a lot about psychopaths and remember its an ambiguous term. in general a psychopath would lack the ability for empathy, fear, and be more-or-less an unconscious being completely enslaved to the passions. (a la Forrest Gump or Jack Nicholson in The Departed - not the Shining) so some benefits would be that you would perform well under pressure, could inflict harm without remorse, immediately recover from a breakup, make a great daredevil or militant - however, you wouldn't be able to appreciate much of anything outside of food, sex, and perhaps dominance. also, if you're both a psychopath and a moron you'll probably end up dead or in prison fairly young.
the right combination of drugs could, depending on the individual, alter a brain enough to produce a disposition nearing that of a 'psychopath'. possibly just methamp + opioids (might need to toss in a weak tranquilizer or hypnotic) of course it can't be just anyone and the effects would dissipate
i'm not very psychopathic mainly because of the fear aspect - i feel fear, routinely.
my take/