Tory leadership candidate Michael Gove has said he “deeply regrets” taking cocaine more than 20 years ago.
He told the Daily Mail that he had taken the drug at several “social events” while working as a journalist.
The environment secretary said he believed the “mistake” should not be held against him in his bid to become prime minister.
Members of the party are due to vote for a new party leader after Theresa May stepped down from the role.
Mr Gove, who served as justice secretary from 2015-16, is one of 11 Tory MPs who have said they intend to stand in the contest to replace her, with the winner expected to be announced in late July.
International Development Secretary Rory Stewart, who is one of those standing against him, has already apologised for smoking opium – a class A drug in the UK – at a wedding in Iran 15 years ago.
And Foreign Secretary Jeremy Hunt – another candidate – told the Times he had drunk a cannabis lassi while backpacking through India.
Mr Gove told the Mail: “I took drugs on several occasions at social events more than 20 years ago. At the time I was a young journalist. It was a mistake. I look back and I think I wish I hadn’t done that.
“I didn’t act with an eye to that. The question now is that people should look at my record as a politician and ask themselves, ‘Is this person we see ready to lead now?’
“I have seen the damage drugs can do to others and that is why I deeply regret the decisions I took,” he added.
BBC political correspondent Nick Eardley said, as a frontrunner for the leadership contest, Mr Gove’s confession was more significant than Mr Stewart’s.
He added it could take a few days for any impact on the leadership race to become apparent but that Mr Gove would be hoping his support in parliament and the wider Conservative Party did not take a dent.
‘Praised for his candour’
Speaking to BBC Radio 4’s Today programme, Daily Mail assistant editor Simon Walters – who interviewed Mr Gove – said the confession was unlikely to affect support from MPs or party members in London – but that could change further away from the capital.
He said: “In London, in metro-land, Tories in leafy Putney won’t think much about it… but out in places like Petersfield in Hampshire when the membership decides, they take a more traditional view about these things and they may well feel it’s a serious matter.”
He added: “I think he should be praised for his candour.”
Mr Gove’s fellow Tory leadership hopeful Dominic Raab, who has previously admitted smoking cannabis, told Today: “I think Michael has set out that he made a mistake.
“It was a long time ago, people will judge it as it is but I do believe in a second chance society.”
He added: “I certainly don’t feel it’s barred him from this race in any way.”
On Friday, Mrs May officially stepped down as the leader of the Conservative Party, but will remain as prime minister until her successor is chosen.
Leadership nominations will close at 17:00 BST on Monday, the party has said.
Leadership candidates need eight MPs to back them. MPs will then vote for their preferred candidates in a series of secret ballots held on 13, 18, 19 and 20 June.
The final two will be put to a vote of members of the wider Conservative Party from 22 June, with the winner expected to be announced about four weeks later.