Mr Cameron has said politicians are entitled to a private past
David Cameron has advised people against taking drugs, following newspaper allegations that he had smoked cannabis as a schoolboy.
Asked whether cannabis use was wrong, he said: "It is something I would advise strongly against. Drug taking is against the law and it's wrong."
He has refused to confirm or deny the cannabis use claims, saying politicians were entitled to a "private past".
But he has admitted there were things in his past that he regretted.
While on a trip to Stockholm on Monday, Mr Cameron was questioned about the story - which surfaced in a book - serialised in the Independent on Sunday.
Both the Independent and the Mail on Sunday reported that school authorities called the police to investigate drug use among pupils at Eton, 25 years ago.
They reported that a 15-year-old Mr Cameron was not expelled, as were some other boys, because he had smoked cannabis but not sold it.
Asked about his views on cannabis use on Monday, Mr Cameron told the BBC: "I have seen contemporaries, constituents who have got into terrible trouble with drugs and their lives have gone into a downward spiral.
"I have always said we need to have better drugs education in schools, we need to have better treatment programmes so we can get addicts off the streets and into treatment to cut the crime that they are committing and make our society safer.
"So we need to have sensible drug policies in this country."
He added: "When younger, lots of people do things that they shouldn't - I was one of them - and I regret those things but I think people should judge me now on the policies we have put forward."
A number of Tory frontbenchers have spoken publicly to defend Mr Cameron and to support his refusal to speak about his private life before politics.
And even Labour Home Secretary John Reid appeared to agree that politicians were entitled to a private life before being elected to office.
"I think this is one of those 'so what' moments," he told the BBC's Politics Show.