Kelly in the Media

The Opposition and crossbench MPs had joined forces in Parliament to allow users of the drug to seek the approval of a doctor to defend any drug-driving charges if they were tested by police and brought to court.

However, Mr Picton said this created a “risky” loophole and he would move to reverse the rule when Parliament resumes this week from the winter break.

“The very clear advice we have from SA Health (and) the Australian Medical Association is that a doctor won’t be able to confidently say to somebody ‘This is safe to use in a driving situation’,” he said.

“I don’t see how we could support a law that allows some people to get behind the wheel of a car … and put people at risk.”

People who are found to have THC — the active drug in the cannabis plant — in their system are currently given a written direction not to drive for five hours.

In July, Dignity Party MP Kelly Vincent moved in Parliament’s Upper House to allow medicinal cannabis users to drive if they had a certificate from their doctor.

She was supported by Liberal and crossbench MPs.

Ms Vincent’s proposal would require patients to be approved by a doctor as competent to drive while on the drug, in much the same way as drivers who take strong medications are tested now.

The change cannot become law without also receiving approval from Parliament’s Lower House, where Mr Picton will this week try to overturn it.

Liberal police spokesman Stephan Knoll said his party would continue to support allowing medicinal cannabis users to drive because the vast majority of the drug variants prescribed by doctors did not have a psychoactive effect.

“You’re still going to be stopped on the side of the road (by a police drug test) but you’ll then have to prove in court — through having gone to a doctor — that you weren’t under the influence while driving,” Mr Knoll said.

“(The change) is only a defence to a prosecution.”

In April, the State Government reduced restrictions on approved cannabis medicines so doctors can now prescribe them for periods of two months without having to seek state approval.

Between 2012 and 2016 there were 4,474 people who tested positive for THC while driving on South Australian roads.