Charlize Theron ''got hit in the face with depression'' after piling on the pounds for her role in 'Tully'.

The 42-year-old actress gained almost 50lbs in less than four months to portray Marlo in the new drama and she admitted she wasn't much ''fun'' to be around during the shoot.

She said: ''I gained close to 50 pounds for this film. I just I wanted to feel what this woman felt, and I think that was a way for me to get closer to her and get into that mindset.

''You know, it was a huge surprise to me. I got hit in the face pretty hard with depression.

''Yeah, for the first time in my life I was eating so much processed foods and I drank way too much sugar. I was not that fun to be around on this film.''

While Charlize - who has children Jackson, six, and two-year-old August - enjoyed the first few weeks of tucking into whatever she fancied, it quickly became a chore.

She told 'Entertainment Tonight': ''The first three weeks are always fun because you're just like a kid in a candy store. So it was fun to go and have breakfast at In-N-Out and have two milkshakes.

''And then after three weeks, it's not fun anymore. Like, all of a sudden you're just done eating that amount and then it becomes a job. I remember having to set my alarm in the middle of the night in order to just maintain [the weight].

''I would literally wake up at two in the morning and I'd have a cup of cold macaroni and cheese just next to me.

''I would wake up and I would just eat it...I would just, like, shove it in my throat. It's hard to maintain that weight.''

The Oscar-winning actress took around 18 months to shed the weight again and admitted it ''was hell'' trying to get her usual physique back.

She said: ''There's nothing fun about that. It took about a year and a half. It was a long journey, very long journey.''

Charlize previously gained a lot of weight for her role in 'Monster' and she admitted she was ''worried'' because it took her far longer to lose the pounds again this time around.

She said: ''I was worried. I was like, this is taking a really long time.

''Because on 'Monster', I just didn't snack for five days and I was fine. You know your body at 27 is a little different than your body at 43, and my doctor made sure to make me very aware of that. Like, you are 42, calm down, you're not dying, all good.''