The Natural Born Killers star portrays an unhinged Los Angeles Police Department officer in the drama, but getting into character took its toll on Harrelson.
He tells The Guardian Weekend magazine, "It was an intense time. The problem was being seeped in paranoia because that was so much the attitude of the character. That really affected me because I don't normally do paranoia. Well, sometimes, of course. But it's an emotion I try not to affect myself with.
"I had weird s**t happening. Not stuff I'd care to talk about. But (sic) being aggressive and strange with friends who had not been offensive, but I took it as offensive. A couple of friends said, 'I can't wait till you're done with this role because I know this ain't you doing it.'"