Green’s Dictionary of Slang

pertaining to drug use/users.

1971		L. Bangs in Psychotic Reactions (1988) 63: If your school or hotrod or doper clique ever really did get that loose, you would be so heavy you would pierce the very ground.
1996		Eble Sl. and Sociability 33: Some of the slang items built by the addition of -er are [...] doper ‘that which is associated with marijuana smoking’ (‘The doper music is loud tonight’).
2000		F.X. Toole Rope Burns 162: The irony of being a doper cop hit him in the face like a slab of hog liver.