Talking about her time as a singer before finding fame in Black Eyed Peas, the 42-year-old said her vice was the drug crystal meth - commonly known as ice - and became so paranoid she thought the Federal Bureau of Investigation was tracking her.
The singer revealed she was hallucinating daily when taking drugs.
Fergie - real name Stacey Ann Ferguson - went into specific detail about the after effects of the strong stimulant: 'At my lowest point, I was [suffering from] chemically-induced psychosis and dementia'. "I was hallucinating on a daily basis", she told iNews.
"It took a year after getting off that drug for the chemicals in my brain to settle so that I stopped seeing things", the mother to Axl, 4 (with Duhamel), continued. Recalling one particular incident where her paranoia was at an all-time high, Fergie explained she thought the "CIA, FBI and a SWAT team" were tracking her, so she made a decision to attempt to seek refuge in a church.
She confessed that she even sought refuge in a church, and this probably happened because she was raised Catholic.
"I remember thinking: 'If I walk outside, and the SWAT team's out there, I was right all along". "And if it really is the drugs, I don't want to live my life like this any more, anyway'".
Now a mum-of-one, the singer said the "drugs thing" was "a hell of a lot of fun" but is thankful she was able to overcome it. "It was a freeing moment".
The beauty was recording her new album Double Dutchess, which she released two months ago, in the middle of splitting from her husband and she used the heartache and pain she was going through to help write some of the tracks. "Because that's my strength, my faith, my hope for something better", she said. That's why we wanted to find our footing with our separation before we announced it publicly: to make sure we really got it together for our kid'.