The film, which opened Friday and focuses on what it says is the United States' often misguided war on drugs, features interviews with celebrity activists like Russell Simmons and Woody Harrelson.
Eminem spoke of his addition to prescription pills, which he came clean about in his 2010 album "Recovery."
"When I took my first Vicodin, it was like this feeling of 'Ahh.' Like everything was not only mellow, but [I] didn't feel any pain," Eminem said in the documentary. "I don't know at what point exactly it started to be a problem. I just remember liking it more and more. People tried to tell me that I had a problem."
A combination of Xanax, Valium and Vicodin landed the rapper in the hospital in critical condition at one point.
"Had I got to the hospital about two hours later, I would have died. My organs were shutting down. My liver, kidneys, everything," he said. "They were gonna have to put me on dialysis. They didn't think I was gonna make it. My bottom was gonna be death."