The Girls actor and his co-star Andrew Garfield both lost more than 30 pounds (13 kilograms) to play two 17th-century Jesuit priests who are persecuted in Japan in Martin Scorsese's latest movie.

Adam admits the shoot in Taiwan last year (14) was gruelling because he was dealing with sweltering heat, hunger and extreme tiredness as his weight loss pills kept awake at night.

"It made sense: we were playing Jesuit priests in the 17th century who were starved and beaten," he tells Britain's Telegraph magazine. "But it was one of the hardest things I've had to do... just because of the physical toll it takes on you.

"Sometimes you would show up to do scenes and all you had energy for was just to listen and respond. But then sometimes a scene wasn't working and you're like, 'I have no idea how to figure this out!' Plus you're waking up three times a night to go the bathroom because you're taking these water pills to drop weight."

He had three weeks to return to his usual weight before shooting resumed for TV series Girls. Recalling the sensation of eating normally again, he says, "The first time I had a scoop of peanut butter, I could literally feel my brain turn on. Suddenly, you're like, 'Oh my God, I can think again!'"

Adam's co-star Liam Neeson sparked fears for his health when he was pictured looking thin and frail in July (15). He lost 20 pounds (nine kilograms) for the role, and he previously told that Adam's military background meant the young actor took the weight loss a lot further than the others.

"Martin (Scorsese) wanted us all to look a bit more gaunt...," Neeson said. "I know Adam went to the extreme. He's an ex Marine and when he's given an order, he follows it through. He was like something out of Auschwitz. Martin requires this level of (dedication) and I think it pays off."

Adam trained as a U.S. Marine but was discharged before he was deployed to Iraq in 2004 following a motorcycle crash.