A drugged motorist has been acquitted of dangerous driving after experts said being on ice could have a positive effect on driving ability.

Leah Lenarczyk, 39, who had a mid-level concentration of methylamphetamine in her system, beat a dangerous driving charge in the South Australian District Court over hitting and seriously injuring a 12-year-old boy after running a red light in 2012.

She was found guilty of a lesser charge of driving without due care.

• Stephen Dank banned for life from AFL
• Treasury snubs negative gearing
• Australia Post slashes jobs

The case has raised concerns from police and road safety authorities who will study the verdict to see if laws need to be changed.

Judge Barry Beazley said the prosecution had not proved that methylamphetamine had seriously affected the woman’s driving after two expert witnesses said ice, while illegal, could have positive effects on driver alertness, depending on its concentration.

The driver was on the substance known as ice. Photo: AAP

Professor Jason White, from the University of South Australia, told the court that taking ice could make people aggressive and agitated but could also reduce fatigue and increase mental and physical performance.

Clinical forensic toxicologist Michael Robertson said the effects of ice included increased mental awareness and improved alertness and concentration.

Judge Beazley noted that the District Court was not a “court of morals”.

“The fact that the accused had consumed an illicit drug is of no relevance, save that it had an adverse effect upon her driving,” he said.

On that point he was satisfied that Ms Lenarczyk was not so affected by ice that she was incapable of effective control of her car.

Assistant Police Commissioner Linda Williams said while each case had to be considered on its merits, police would study the verdict and work with the state government to consider if legislative changes were required.

But she said driving while drugged remained an offence and it would be “business as usual” for police.

“We will still be out there looking for people drink-driving and drug-driving,” she said on Friday.

“We would want people to be very clear that this is a dangerous pastime if you’re going to take drugs and drive a car.”

The Motor Accident Commission said it would also review the verdict.

“Last year 24 per cent of people killed on our roads had some type of illegal drug in their system,” the commission’s general manager of road safety Michael Cornish said.

“Drug driving does affect your behaviour on the road and increases the risk, not only to yourself, but to the community at large.”

– AAP