The Greens want to legalise cannabis for Australians over the age of 18, in a bid to take the drug out of the hands of criminal dealers.

Key points: Richard Di Natale says cannabis needs to be sold in a "more tightly controlled" environment

Richard Di Natale says cannabis needs to be sold in a "more tightly controlled" environment He says countries that have legalised cannabis have seen a drop in drug-related crime

He says countries that have legalised cannabis have seen a drop in drug-related crime Under the plan there would be strict penalties for people caught selling to minors

Senator Richard Di Natale argued his party's proposal would not result in the widespread sale and use of cannabis, and claimed there would be strict regulations on sale and production.

The policy has support from former Australian Federal Police (AFP) commissioner Mick Palmer.

As part of the plan, an agency would be created to be the sole wholesaler of cannabis, as well as the outlet responsible for issuing licenses for prospective growers and retailers.

"As someone who was a drug and alcohol doctor, I've seen how damaging the tough on drugs approach is to people," Senator Di Natale told Channel Ten.

"We've got to take this out of the hands of criminals and dealers, [and] we've got to make sure it's within the hands of health professionals."

"We've got to have a much more tightly controlled and regulated environment."

The Greens have urged Australians to look to the United States, Spain and Uruguay as examples of legalising cannabis leading to a drop in drug-related crime, and argued it could also provide welcome revenue through the taxation system.

Under the minor party's plan, there would be strict penalties for people caught selling cannabis to minors.

Adults would be allowed to grow up to six cannabis plants for personal use.

Senator Di Natale said it was more harmful to continue banning the use of cannabis, and called on Australia to "get real".

"Nearly 7 million Australians choose to use cannabis," he said.

"That choice can land them with a criminal conviction, which can impact their opportunity to get an job.

"They're sourcing products of unknown quality and purity, and of course all they're doing is feeding the mega profits of criminal syndicates and criminal gangs."

AMA rules out support

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The Australian Medical Association (AMA) said it could not support the Greens' plan because of the serious physical and mental health impacts of cannabis use.

Mr Palmer maintained that while he was not generally a supporter of Senator Di Natale's party and policies, he did see merit in the idea of decriminalising cannabis.

"The very nature of law enforcement, when you have it focused on this sort of 'use and possess' crime or activity, is that it will discriminate against people that are most vulnerable," he told the ABC's AM program.

"People most likely to come to notice of police are Indigenous people, homeless people, people who suffer mental health and other health related problems, including people like Vietnam vets.

"We're not winning the war against drugs with the process we're using at the moment. We can't possibly win it."

Not all law enforcement experts agree.

Former WA police commissioner Karl O'Callaghan's son has battled drug addition, and he is worried decriminalising cannabis could trigger or exacerbate mental health problems.

"They may have an inability to function or work, and I think they're the problems that we should be concerned about when people move to make cannabis more widely available," he told AM.

"They are very significant and trying to get adequate help, even today, without decriminalisation is very, very difficult.

"I would be concerned that parents would be left with nowhere to turn if the services are not in place as a result of this proposed policy."

The Greens argue tax revenue from cannabis sales would be spent on mental health services, but the party has not specified how much money could be raised or how much would be spent in the sector.