Paul McCartney has quit drugs for the sake of his eight-year-old daughter, Beatrice.

The former Beatle, who was once jailed in Japan for marijuana possession, tells Rolling Stone magazine that he no longer uses illegal substances.

He says, "I did a lot, and it was enough... When you're bringing up a youngster, your sense of responsibility does kick in, if you're lucky, at some point. Enough's enough - you just don't seem to think it's necessary."

But the "Maybe I'm Amazed" singer, who has been a fervent advocate for the legalisation of pot in the past, is surprised activists haven't won that battle yet - although he can now understand the other side of the argument.

He adds, "It's such a difficult argument... You know the argument that if booze is legal, why not that, and then the argument against it is that we don't need another (legal drug)... I'm not going to be the judge of how to deal with it; somebody else can figure that out."

Beatrice is McCartney's daughter from his second marriage to Heather Mills.