Michael Caine "nearly got a hernia" from smoking Marijuana.
The 'Harry Brown' actor said he was never a fan of drugs, and the only time he ever smoked cannabis it had a devastating effect on him.
He said: "Marijuana seemed like the most innocent of drugs, but I read it affects your memory.
"I thought, 'I can't do it because I'll forget my lines.' Then one day I did smoke a marijuana cigarette and I started to laugh and I laughed for five hours.
"I nearly got a hernia, so I thought, 's*d that' and never got started on drugs.
The veteran actor, 76, said he was much happier drinking beer.
He added: "I drank a lot of alcohol - that was my drug. I was never an alcoholic, but I could get drunk every now and again. You can get bombed on English beer very easily."
Michael also defended the actions of peers in the 60s - when his hometown of London was awash with casual sex and drugs - saying it was natural to a generation growing up in the wake of World War II.
He added: "It was amazing. It was a time when the British working class said, 'We're going to enjoy ourselves'. You have to remember, we'd just had a war.
'Harry Brown' is released in UK cinemas on November 11.