I have a friend who was pretty out of control for a while, constantly doing coke, ketamine and acid at the same time, plus random pills. He now only smokes weed, and he smoked a fuckload. He smokes more weed than anyone I've ever known and i know alot of stoners. I don't know how he maintains productivity, or wakefulness for that matter! But he does a great job so I guess it works for some people. For me though, weed is my main addiction. Being stoned doesnt cause me to crave other drugs, but other drugs, especially psychedelics, make me need pot.