Stress for me is a killer, by Friday night if I've had a hard week I'm either wishing I still had a pot dealer or I'm hitting up the liquor store for some whiskey.
Similarly high IQ is linked to depression, again likely for a mix of reasons from social isolation (aka being smarter than everyone) and having a greater ability for introspection into ones life (aka I could have done more with my life, etc.). Depression is often a major factor in alcoholism and drug abuse.
The question I wonder is does a high IQ predetermine what drugs a person is going to use. Smart people I've noticed seem to target pot and hallucinogenics. It always seems to be the idiots and suggestibles that end up with the heroin addiction.