The Beatles musician has smoked the herbal drug since the band`s heyday in the 60s, but has given up marijuana
so he can be a better parent to his eight-year-old daughter, Beatrice, his child with ex-wife Heather Mills.
He told Rolling Stone magazine: "I did a lot, and it was enough. I smoked my share.
"When you`re bringing up a youngster, your sense of responsibility does kick in. Enough`s enough - you just don`t seem to think it`s necessary."
Paul - who is now married to American heiress Nancy Shevell - has previously confessed to using cocaine and trying heroin once when he was in The Beatles.
Speaking about his experiences with the drugs in a magazine interview in 2004, he said: "I tried heroin just the once. Even then, I didn`t realise I`d taken it. I was just handed something, smoked it, then found out what it was.
"It didn`t do anything for me, which was lucky because I wouldn`t have fancied heading down that road.
"I did cocaine for about a year around the time of `Sgt. Pepper...`
"Coke and maybe some grass to balance it out. I was never completely crazy with cocaine.
"I`d been introduced to it and at first it seemed OK, like anything that`s new and stimulating. When you start working your way through it, you start thinking, `Mmm, this is not so cool an idea,` especially when you start getting those terrible comedowns."
Paul and his first wife Linda - who passed away in 1998 - both used to smoke marijuana, but he was given a wake up call when he was put in prison for nine days in 1981, for trying to take the drug into Japan during a tour.
Of his ordeal, he said: "I kept thinking, `What have I done to my family?` I was thrown into nine days of turmoil. It was very, very scary."