I don't watch movies on drugs, but I love tripped out movies so what I list would probably kick arse on drugs anyways - I will try not to repeat what others have said, too.
*Delicatessen
*Barraccuda (sp?)
*Dead Man
*Time Bandits
*Vidiot from the UHF
*ANYTHING BY DAVID LYNCH (but it might send too many people too a bad place)
*Episodes of Gumby (preferably those featuring evil gumby - boy was he evil!)
*Legend of the Overfiend (Manga film - I've forgotten the Japanese name)
*Virgin Suicides
*Jesus' Son
*American Beer
I'll think of some more later...
BTW - Sadly, Jeff Mills made a different edit of Metropolis to go with his soundtrack so it wouldn't match up if put with the Georgio Moroder Version (not for that express purpose, of course).