What kind of damage can drugs do to your brain? Specifically Opiates and Alcohol?

Because my dad is not all there. And he has a history of abuse with those two drugs. Memory loss, nodding in and out, etc are symptoms of his behavior.

: http://alcoholdrugstreatment.info/what-kind-of-damage-can-drugs-do-to-your-brain-specifically-opiates-and-alcohol