The 55-year-old actress - who won the Academy Award for Best Supporting Actress in recognition of her role as Oda Mae Brown in `Ghost` - was so nervous before the prestigious ceremony, she smoked some pot in the hope of "relaxing herself".
She said: "I learned a great lesson though. Never smoke pot before there`s the possibility of having to talk to one hundred million people. Smoking cigarettes and pot every now and then are one thing that relaxes me and I thought, `I`ve got to relax.-
"So I smoked this joint that was the last of my home grown and honey, when he said my name and I popped up, I was like, `Oh f**k, oh f**k, up the stairs one two three four five, onto the podium. There`s millions of people, OK grab the statue.- I knew I should have never had done it."
However, the `Sister Act` star admitted as soon as her mother saw her accept the award she realised she was under the influence of a drug.
Speaking during a voiceover session for her 1992 movie `The Pagemaster` in a video obtained by gossip website TMZ, Whoopi added: "My mother called me afterwards and said, `You smoked didn`t you? Your eyes were just glistening.-
"So I panicked and got the Oscars tape to see whether you could tell and you just couldn`t. I know you`re not supposed to admit that you smoke pot but I don`t drink alcohol!"