every bottle of opiate based drugs i've ever got my hands on have said that using them could cause severe liver damage, but who knows how true that is, and you risk it anyway with alcohol, so...
I can say, though, that there is definitely less of an after effect using opiates than benzos. Which is to say, pop a vicodin and you feel fine the next day, but pop a xanax and you still feel a little out of it/hazy when you wake up.