The father of a young girl who uses medicinal cannabis to treat her severe form of epilepsy has vowed to continue lobbying for law reform, after being found guilty of charges of possession and cultivation.

Michael Lambert was surrounded by his family, including his five-year old daughter Katelyn, when the magistrate handed down his decision in Gosford Local Court today.

Katelyn suffers a debilitating form of epilepsy known as Dravet Syndrome but her doctors have seen a remarkable improvement in her condition since she started taking imported cannabis oil in 2014.

Mr Lambert admitted to the charges but argued he had no choice but to help treat his daughter, who had already suffered irreparable brain damage because of regular, severe seizures.

He said he began cultivating the drug as a back-up out of fear the supply could be cut off at any time.

"I was just a normal father trying to do the best by my daughter ... I just did what I had to do to save my daughter's life and the court has found that I'm a criminal," he said.

"I knew this was a high hurdle to win.

"If Katelyn can't win on medical necessity, then nobody can win on medical necessity."

'Science can't circumvent law'

In handing down his lengthy judgement, Magistrate Bruce Williams acknowledged medical evidence from Katelyn's doctors that her health significantly improved after taking the oil but maintained the court "couldn't set a moral policy".

Katelyn's father Michael says since taking medicinal cannabis his daughter's quality of life has improved significantly. ( Supplied: Barry Lambert )

He told the court there was no doubt science was "in a state of flux" on medicinal cannabis and research was ongoing but no-one could "circumvent the law".

He found Mr Lambert guilty of the two charges but he did not record a conviction.

Outside court, Mr Lambert said it was up to authorities to change the law to help countless other families like his own.

"To give people like myself a defence for saving their child's life when they have no other choice," he said.

"We didn't prefer cannabis medicine over any other medicine.

"Hold your breath for five years until there's an approved medicine a doctor can prescribe because there is no approved medicine.

"There's only untested medicines. He just blamed me for using an untested medicine but that's the Government's policy at the moment."

Family calling for register to protect those using hemp oil

Mr Lambert did not hold back on taking a swipe at the NSW Government.

"She's (Katelyn) got brain damage, she's permanently disabled but she's smarter than the Health Minister of NSW and got more compassion than Gladys Berejiklian," he said.

"They don't care."

Katelyn Lambert suffered permanent brain damage due to the seizures she was having. ( ABC News: Meredith Griffiths )

Katelyn's grandfather, Barry Lambert, who has investments in the medicinal cannabis industry, said the Government should consider an interim measure in the form of a special register to protect citizens.

"The states should declare a register where people like Katelyn can register and they can test the oil to make sure there's nothing harmful about it," he said.

"The problem in NSW is confusion with marijuana and this is not what that debate's about here. We're not arguing about that ... that's a different issue.

"The fact is hemp extract is wonderful for various conditions, in particular epilepsy."

The Lambert family is preparing to discuss the matter further with NSW Premier Gladys Berejiklian later this month, and has also been approached by Federal Liberal Democrat, David Leyonhjelm.

The case comes just weeks after new scientific evidence, published in the New England Journal of Medicine, showed that medicinal cannabis helps children with severe epilepsy.