Jada Pinkett Smith once "passed out" on set after taking a "bad batch of ecstasy".
The 49-year-old actress admitted the "eye opening" incident - which took place when she was working on 1996 movie 'The Nutty Professor' - served as a wake-up call to her over her relationship with drugs and alcohol.
Speaking on the latest episode of 'Red Table Talk', she said: "I had one incident on 'Nutty Professor'. I went to work high and it was a bad batch of ecstasy."
But Jada lied to her colleagues about the incident, though it made her vow to change her habits.
She added: "I told everybody that I must’ve had old medication in a vitamin bottle. That’s what I said. ... But I tell you what I did though. Got my ass together and got on that set. That was the last time.
Since then, the 'Girl's Trip' star has been "cold turkey", aside from an occasional glass of red wine.
She added: “I cannot touch vodka. I cannot touch rum. Rum’s another one. No dark liquor.”
Although she didn't use drugs or alcohol every day, Jada - who has children Willow and Jaden with husband Willow Smith - admitted there was a time when she was a "weekend party girl" and began taking increasingly stronger substances to sustain her highs.
She said: "Your threshold becomes so high that what it takes for you to get to the place you need to get to.
"It'll take me two bottles to get to—okay, if I do ecstasy, weed, and alcohol at the same time, I'm gonna get there faster and I can keep the high going because then I can just keep drinking 'cause I know ecstasy's gonna last me about three, four, five hours.
"The weed, you know, that's just gonna keep me just smooth. And then the alcohol's gonna keep it going. I can just keep taking drink, drink, drink."