WMG / Empire Records

There really was only "lots of sugar" in Eddie's brownies.
It could be that Mark is so weird on his own that he doesn't even need drugs to see himself in a Gwar video.

Lucas has a anti-social disorder

Lucas believes the store has magical powers
Several remarks he makes seem to imply that Lucas believes that the store is in some way magical, and benevolently so at that. Notably, his claim to be "guided by a force much greater than luck", and his assertion that nothing bad would happen to Debra now that she was "in the store."