The Sweeney star sheds his tough guy image to play a man diagnosed with the condition, which causes severe memory loss and confusion.
DVDs of the thriller, which also features Jim Sturgess, are set to hit stores in the U.K. later this month (Jan13), but Winstone is upset the movie did not make it to the big screen.
He tells Britain's Metro newspaper, "(The film) is about a serious illness that affects a hell of a lot of people. I wanted to do it justice. Trying to combine the illness and a thriller and come out the other end with the final film was rewarding.
"The disappointment was we couldn't find anyone to put it in the cinemas. It's disappointing when you can't get a release because of the subject. Films sometimes have something to say and we don't get to see them."