Ms Allan, who took over from Daniel Andrews as premier in September, was asked if she had smoked or consumed the psychoactive drug.

"It was a long, long time ago," she told reporters on Thursday.

"It's important that we object a sense of honesty into our contributions on this because it is a real issue for many in our community and it's best that we take a harm-minimisation approach."

The admission came after Victoria's upper house debated a bill to regulate adult use of cannabis on Wednesday.

While the government did not back it, Mental Health Minister Ingrid Stitt said it was "amenable" to discussions with the crossbench and taking advice from experts.

Ms Allan stressed the government had no plans to decriminalise adult use of cannabis and defended listening to experts on the topic.

"It doesn't necessarily mean that there's a change to government policy," she said.

Treasurer Tim Pallas said his view was Victoria should not have a criminal-approach to the drug.

"I should declare, I have used," he said.

Opposition Leader John Pesutto joined the procession of admitted users, saying he tried the drug three times at university.

"I'm not proud of it," he said, adding he did not support cannabis being legalised because of concerns about health impacts.

Data shows almost 40 per cent of Victorians have used cannabis, the Victorian Alcohol and Drug Association says.

Its chief executive Chris Christoforou commended the trio for having the courage to out their past cannabis experiences, given the stigma attached with using alcohol and other drugs.

"Admissions such as these from political leaders have the ability to humanise the issue, supporting those experiencing problems with alcohol and other drugs that they are not alone," he said.

"We encourage our political leaders to reflect on the need to progress cannabis law reform in Victoria."

The private member's bill, led by Legalise Cannabis Victoria, proposed legalising personal adult consumption but not in public.

Other features would have allowed adults to possess a small quantity of cannabis and for six plants to be grown at each home.

The state's independent Parliamentary Budget Office estimates Victorians spend up to $1.2 billion on cannabis through the illegal market each year.

Legalise Cannabis MP David Ettershank said it was safe to assume more MPs had consumed the drug.

"With legalising cannabis, it's not a question of if it's going to happen, it's a question of when and how," he said.

A parliamentary inquiry on Thursday also called for the government to create legislation to manage the industrial hemp industry.

Victoria was one of the first states in Australia to re-legalise industrial hemp in 1998.

But inquiry chair and crossbench MP Georgie Purcell said hemp farming and manufacture remained stunted due to prohibitive regulation, licensing and planning rules.

One of the inquiry's nine recommendations was to amend the Drugs, Poisons and Controlled Substances Act to remove industrial hemp and instead create separate legislation, in line with all other Australian states.

Australian Associated Press