The opposition says SA needs to participate with the other states on a focused regime covering the use of medicinal marijuana.

The South Australian opposition has called on the state to join the national research effort on medicinal cannabis.

Opposition Leader Steven Marshall said SA was the only state not engaged with the clinical trials being conducted in NSW.

The trials are looking at providing medical cannabis to children with severe, drug-resistant epilepsy, adults with a terminal illness and adults with chemotherapy-induced nausea and vomiting.

"The tardiness of the government in joining this national effort to improve the lives of people suffering a range of severe afflictions is disappointing," Mr Marshall said on Tuesday.

"Australian governments are looking at the use of medicinal cannabis - South Australia needs to be part of developing a focused regime which supports improved health outcomes."

The opposition said the government should appoint a South Australian observer to the trials and have local medical researchers plan for SA to participate.

The SA Greens will host a forum for MPs on Friday to discuss the need for sick and suffering South Australians to take part in the trials.

"South Australia needs to get in the game," Greens MP Tammy Franks said.

Health Minister Jack Snelling said the state government supported and would closely monitor the NSW trials.

But he said there were no plans to start a separate trial or replicate what was already happening.

"Medical opinion is currently divided on the use of medical marijuana,'' Mr Snelling told AAP. ``There are already patients that will be participating in these trials and we will monitor it closely."