Well I suppose if a high percentage of people in bands, like nothing more than getting completely off their faces, then there's bound to be quite a few songs about drugs. My top 5 are:

1 Feels Good Hits of the Summer - QOTSA
2 Heroin - Velvet Underground
3 Don't Fight It Feel It - Primal
Scream
4 Eight Miles High - Byrds
5 Under The Bridge - RHCP