A Greens senator says it's cruel to deny the ill access to medical cannabis because of the stigma associated with it.

Senator Richard di Natale, who is a doctor, says there's clear evidence that medical cannabis can be very effective for prescribed medical purposes.

"I just think it's cruel to deny people the option just because there's some stigma associated with it," he told the Nine Network on Sunday, amid a renewed push to legalise the drug for medical use.

"We're going to push to try and get people on all sides of politics to back this reform.

"The science and the evidence is very, very clear."