The 48-year-old actor said while he was shooting "Mission: Impossible III" in 2006, he was "fairly lost, and unhappy, and an alcoholic".
"It was awful, terrible," he told The Guardian while talking about his struggle. "It owned me."
"When I watch that film back, I can see where I was then, which was fairly lost, and unhappy, and an alcoholic," Pegg added.
The actor said he "micro managed" his condition for quite some time, till the ball dropped.
"One thing (addiction) does is make you clever at not giving anything away. People think junkies and alcoholics are slovenly, unmotivated people. They're not they are incredibly organised. They can nip out for a quick shot of whisky and you wouldn't know they have gone. It's as if you are micro-managed by it," Pegg said.
"But eventually the signs are too obvious. You have taken the dog for one too many walks," he added.
Pegg revealed that while he was on a trip to Comic-Con to promote his 2011 movie "Paul", he went missing for four days.
The actor said when he returned to the UK, his home, he went into rehab which helped him turn his life around.
"I got into it. I got into the reasons I was feeling that way. I went into AA (Alcoholics Anonymous) for a while, too. I don't think I would be here now if I hadn't had help," he said.
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