Marijuana Gin was a mind-bending beverage imbibed by Dave Lister, at least according to Arnold Rimmer.
Given the name, it was apparently gin imbued with cannabis. It is unclear whether this was actually drank by Lister, or if it was merely Rimmer talking in hyperbole.
Rimmer accused Lister of being on it "again" after Lister described the first future echo, which Rimmer hadn't experienced yet. ("Future Echoes", Series I)