Daniel Radcliffe says he turned up to the Harry Potter set drunk, with many scenes where he was "dead behind the eyes''.
The 22-year-old Harry Potter star, who is promoting his new film Woman in Black, said that he had a "very addictive personality'' and "drank a lot''.
"It was bad. I don't want to go into details but I drank a lot and it was daily - I mean nightly,'' he told UK's Heat Magazine.
"I can honestly say I never drank at work on Harry Potter. I went into work still drunk, but I never drank at work. I can point to many scenes where I'm just gone. Dead behind the eyes.''
Radcliffe, who quit drinking when he was 21, told UK's Shortlist magazine his heavy drinking was affecting his social life.
"I was living in constant fear of who I'd meet, what I might have said to them, what I might have done with them, so I'd stay in my apartment for days and drink alone,'' he said.
"I was a recluse at 20. It was pathetic - it wasn't me. I'm a fun, polite person and it turned me into a rude bore."
The young star said "blacking out was my thing'' and he could not remember his "couple of fun drunken nights out''.
Radcliffe said while people told him he had a problem, it was only when he acknowledged it itself that he was able to stop drinking.
But now that he was sober, he enjoyed being "smug about it''.
"Actually, after our Christmas party on Broadway, I had fun going into the rooms of people I knew had got really f---ed up the night before, and shouting at them. Just to be an a---hole.''