Liberal Democrats senator David Leyonhjelm believes it's high time to legalise cannabis, but his push is set to remain a pipe dream with legislation likely to go up in smoke.

The Senate is debating his private bill which would allow state and territory governments to legalise and regulate the drug for recreational and medicinal use.

"It is high time we stopped interfering in adult choices," Senator Leyonhjelm told parliament on Monday.

With the coalition and Labor opposed to legalising cannabis, the draft laws will not pass the upper house but debate was adjourned before they were voted on.

Liberal senator Jane Hume cited numerous studies showing harmful effects of marijuana use, including links to mental health issues.

"It's unfathomable that anybody in this place could support a bill that increases a likelihood of teen suicide and of youth dropping out of school," she said.

Senator Leyonhjelm talked up savings for law enforcement and an estimated $300 million boost to GST revenue through regulating the drug.

The Greens also support legalising cannabis after changing their position earlier in the year.

Senator Leyonhjelm couldn't resist a dig at his crossbench sparring partners, taking aim at their old policy which only extended to medicinal use.

"This reflected the core Greens traits of elitism, wowserism and authoritarianism," he said.

Greens leader Richard Di Natale said the so-called war on drugs had been an unmitigated failure.

"It's about time we had some courage from our political leaders, that we recognise we need to start treating drug use as a health issue, not a law and order issue," Senator Di Natale said.

He outlined a plan for a regulated cannabis market with a focus on reducing harmful impacts.

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