Lyric discussion by michvicious 

Cover art for Where My Mouth Is lyrics by Taking Back Sunday

"and i put my money where my mouth was until i couldn't breathe through my nose"

i think that clearly shows that it does have to do with drugs. my interpretation was that the drugs are what changed him and made him lose the friends so of course it's not JUST about drugs but he seems to be saying in plain english that drugs changed him and messed up his life.