The upcoming dramatic comedy stars Ruffalo as Adam, a recovering addict who undergoes a 12-step programme to cope with the condition.
Ruffalo reveals he researched the part by visiting patients in treatment and admits he was stunned by the stories he heard.
He tells New York Magazine, "People say, 'Sex addiction, oh really? Come on, who could get enough of that?' And then you go into these sex-addict meetings, and you hear these stories of people who are masturbating a hundred times a day and have to go to the hospital because there's nothing left and they whittled it down and they're bleeding."
The Avengers star hopes the new movie serves to draw attention to the disorder.
He adds, "I think it seems like so many celebrities and athletes and politicians might use it as a 'get out of jail free' card, but I know a lot of addicts, and so I know how there's a lot of bad behaviour that can be chalked up to any kind of addiction. For a long time, I don't think people believed in alcoholism, you know, and I think we're probably at the threshold of a decade of serious sex addiction."