Lyric discussion by cih420 

Cover art for Opium lyrics by Marcy Playground

I agree Marcy Playgrounds self titled is one of my favorites of all time, however its success as well as downfall was from the success of sex and candy. I believe that the band talked about not includeing this single on their debut cd because it would take away from the other songs, which it did for most people.
Anyway I think this song is about being depressed, and using drugs ( in this case opium ) to get through your depression, until the side effects start to take effect...