"Sometimes publicists get really mad with me for talking about stuff like that — but I don't care," the singer and actress told Britain's Times newspaper.
"For me, it's something I went through," she continued. "It's an epidemic, and it's important to talk about it because it's a very, very hard thing to stop."
The star, who will hit theaters later this fall alongside Penelope Cruz in "Nine," opened up about her drug use in the Sunday edition of the newspaper.
"It started with ecstasy. I loved ecstasy. Loved it, loved it. It was great at first, then it just went…" she added making a downward motion with her hand.
And the star, who previously admitted to having a crystal meth problem, said that drug was a hugely detrimental force.
"It ruins you," she told the paper.
Fergie blames some of her past troubles on having been a child star (she starred on "Kid's Incorporated" as a youngster).
"Definitely. What happens when you're a child professional is that you have to be, well, professional. You're taught not to have tantrums, to always people-please," she said. "That's part of how I got into [drugs] later."
These days though, life is good. She has the band, the movie and a very handsome man, Josh Duhamel, whom she married earlier this year.
But she still has some trouble in the form of the tabloid press.
"I'm trying to get a thicker skin," she said. "I like to be aware of people's perceptions of me, but when you put it as a priority, as a means to judging your worth, that's when it can be dangerous.
"There's no rule book on how to do this," she added.