The West Australian premier has indicated he could support medicinal marijuana being given to patients in palliative care but maintains it is a very damaging drug.

Colin Barnett said he did not support the legalisation of medicinal cannabis, but administering the drug in tablet form would reduce its harmful effects.

"I believe that if you have a person in palliative care, some of the components of that drug can be administered probably by tablet and in a way that doesn't have the other harmful effects of cannabis," Mr Barnett told News Limited on Thursday.

"But it is a very damaging drug, and if we were to just simply say you can have cannabis for medicinal purposes, I think you would see a proliferation of that drug throughout our community."

Mr Barnett has recently kept himself out of the debate to legalise medicinal marijuana, but told parliament in 2010 that there was some scope for therapeutic use of cannabis.

In July, opposition leader Mark McGowan announced WA Labor's plan to legalise cannabis for medicinal use, saying it was a controversial proposal but the right thing to do.

Mr McGowan told the state branch's annual conference that spray or tablet-form cannabinoids were a compassionate and intelligent solution to the pain, vomiting, nausea and poor appetite endured by people who were terminally or chronically ill.

State Health Minister Kim Hames has previously said there was evidence that cannabis and its extracts were beneficial in treating a range of conditions, but more research was needed.

About 250 people attended a rally at the WA Supreme Court Gardens earlier this month, urging the WA government to make marijuana available to those who are sick and dying.

On the same weekend, the Uniting Church's WA synod voted in favour of supporting changes to state law to allow doctors to prescribe the drug, which would be administered under supervision.