In an interview with Huffington Post Canada's Althia Raj, Trudeau said his brother's legal trouble over a small quantity of marijuana was one of the experiences that influenced what he has called an "evolution" in his thinking on marijuana laws.
Trudeau told the Huffington Post that he has smoked marijuana five or six times in his life and that he does not do other drugs and doesn't particularly like to drink alcohol or even coffee.
He said the last time he smoked marijuana was about three years ago.
"We had a few good friends over for a dinner party, our kids were at their grandmother's for the night, and one of our friends lit a joint and passed it around. I had a puff," Trudeau said in the Huffington Post interview.
“I’m not someone who is particularly interested in altered states, but I certainly won’t judge someone else for it," he told Raj.
But, he added, “I think that the prohibition that is currently on marijuana is unjustified.”
Trudeau has come out in favour of the legalization and regulation of pot in recent months after earlier supporting an attempt by the Conservatives to toughen marijuana laws. The government has since passed a law that sets mandatory minimum sentencing for pot possession.
The Huffington Post said it asked all the federal party leaders when they last smoked pot. The Prime Minister's Office said Stephen Harper has never smoked marijuana, pointing out he has asthma, and NDP Leader Tom Mulcair's office said the opposition leader has smoked marijuana but refused to say when.
Brother faced possession charge
Trudeau told the Huffington Post his younger brother Michel, who died in a B.C. avalanche in 1998 at the age of 23, was facing a charge of marijuana possession after a small quantity of pot was found in his car by a police officer following an accident.
"Mich had charges pending against him when he died for marijuana possession even though it was just a tiny amount," Trudeau said, adding that this was a factor in his initial decision to back decriminalization.
Since then, Trudeau said, he has been persuaded by scientific studies and by groups such as NORML Women’s Alliance of Canada, that regulation and taxation of marijuana is the best way to keep it out of the hands of young people.
He said he still believes marijuana is harmful to young people and would support harsher penalties for selling marijuana near a school.
"I do not see this as a slippery slope…. I see this as an issue of legislators slowly catching up to where public opinion and public behaviour actually is," he told the Huffington Post.