Robert Downey Jr believes it will take four years before his fiancee can truly enjoy being with him, because that's how long it will take him to conquer his demons.

The reformed hellraiser has battled addictions for most of his adult life and has warned girlfriend Susan Levin to be patient until he feels truly comfortable in his own skin.

But the CHAPLIN star remains optimistic he will get there eventually.

The 40-year-old says, "I am not used to being happy, because I was really busy either working or getting stoned for the past 14 years.

"I probably should meditate for four years with meal breaks.

"Susan understands she'll probably live another four years with me in hell before we'll be happy. But she gets it: I am a work in progress."