Jeremy Hunt admitted to The Times that he had a "cannabis lassi", a yogurt based drink, when he was backpacking through India as a young man.
Days before Conservative members of parliament open nominations for candidates to be their new leader, Environment Secretary Michael Gove said he used the Class A drug on several occasions when he was working as a journalist.
Raab said he smoked marijuana at uni and Johnson said he'd done both cannabis and cocaine while studying at Oxford.
'It was 20 years ago and yes, it was a mistake, ' he said.
An upcoming biography of Gove includes the revelation of his drug use.
"It was 20 years ago and yes, it was a mistake", he told the Daily Mail newspaper, adding "But I don't believe that past mistakes disqualify you". International Development Secretary Rory Stewart told the Telegraph he smoked opium at a wedding in Iran 15 years ago.
He added: "I think it is the case that, if I were to be elected prime minister of this country, then of course it would be the case that I would be able to go to the United States and I think it's foolish to suggest otherwise".
Speaking on BBC One's Andrew Marr Show, he said: "I do have a profound sense of regret about it all and I am very, very aware of the damage that drugs do".
The Tory leadership hopeful previously admitted taking the class A drug several times when he was a journalist. 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?'
Meanwhile, in what appears to be a current freaky trend of attempting to appear more street-wise and "down-to-earth" to Tory members (i.e. voters in the impending leadership race), Rory Stewart, another of the Tory leadership contenders, recently apologised after admitting he had smoked opium at a wedding in Iran. One of the things that I would absolutely say is it is a mistake which I profoundly regret.
The Conservative Party's 160,000 dues-paying members will vote on the final two candidates to pick the next party leader, who will also become prime minister.
Raab, who had already admitted taking cannabis as a student, said: "At university, I tried cannabis, not very often as I was into sport".
"There was a period before university when I had quite a few (cannabis joints)", he said.