A Mernda couple will continue giving their son illegal cannabis medication, despite hospital orders banning him from using it.

Their defiance comes as Victorian Opposition Leader Daniel Andrews reinforced his pledge to legalise medicinal marijuana, if Labor wins the election.

Three-year-old Cooper Wallace takes cannabis oil four times a day.

“If it's helping him we will continue to do so,” mother Cassie Batten said.

But it's illegal and last week, lawyers from Epping's Northern Hospital banned Cooper from receiving cannabis oil at the facility.

Against doctor's orders, the couple removed Cooper from hospital.

“If they suspected or saw us then they would confiscate it and call the police,” Mrs Batten said.

Today the Opposition reinforced its push to legalise medicinal marijuana.

“A very sad situation where the lawyers are determining the healthcare that Cooper gets, rather than the doctors,” he said.

“I've committed our team to changing this law to drag this law into the 21st century.”

Doctors are divided; while clinical research is encouraging, they warn families shouldn't take matters into their own hands.

“The use of medicinal cannabis needs to be done in controlled circumstances in specific situations,” Dr Tony Bartone said.

The state government has approved more clinical trials of cannabis-based medicines, but today the premier softened his stance, saying patients such as Cooper could apply for an exemption.

But Cooper's parents say, they don't have any time to waste.