Australia's first marijuana trial will get under way in NSW later this year in a bid to provide people suffering chronic pain alternative treatment options.

NSW Premier Bob Carr said the appetite-inducing qualities of marijuana would be legally harnessed under a medicinal cannabis scheme, which was greeted with bipartisan support.

Mr Carr said the trial was aimed at easing the suffering of people who came to the attention of a working party on cannabis he established in 2000.

The premier told parliament it was a compassionate scheme, helping people who suffer from wasting due to cancer and HIV/AIDS, nausea from chemotherapy, severe or chronic pain, muscle spasticity due to multiple sclerosis and spinal cord injuries.

There would be strict safeguards and penalties in the proposed legislation, which will be introduced in the spring session of parliament, he said.

NSW joins nine US states, Canada and the Netherlands in legalising marijuana for medicinal use.

Opposition leader John Brogden gave the proposal his in-principle backing and said initial talks with National Party leader Andrew Stoner indicated it would have coalition support.

Patients would get medical cannabis through a new Office of Medicinal Cannabis within the NSW Health Department, Mr Carr said.

Those convicted of an illicit drug offence (except a minor personal use offence), parolees, minors and pregnant women would not be eligible to register as a user, he said.

Meanwhile, the trial received mixed response from health and community groups.

The NSW Cancer Council cautiously welcomed the plan, saying marijuana could help relieve the pain many cancer patients suffer with treatments like chemotherapy.

But spokeswoman Anita Tang warned smoking was not a good way to take any medication, because of the damaging and cancer-causing effects on the lungs.

The chairman of Quit Marijuana Program at Sydney's Westmead Hospital, Jill Pearman, said the government's plan was "absolutely scandalous" and encouraged NSW taxpayers to protest the move.