FOLLOWING a Lismore magistrate's decision earlier this week to acquit a driver of being under the influence of cannabis, a drug law expert from Southern Cross University has criticised the Random Drug Test regime as prohibition dressed up as road safety.

SCU School of Law and Justice lecturer specialising in drug law Aiden Ricketts condemned the random drug testing regime for not being evidence based and said it risks bringing "the law into disrepute".

"My understanding is that magistrates are very uncomfortable making convictions on this issue because there is no evidenced link between the positive reading on the drug test and the impairment of the driver," Mr Ricketts said.

"Unlike the alcohol laws, where there has been extensive research into the effects alcohol has on our driving and the level of impairment based on the amount of alcohol consumed, there has been insufficient research into the effects of cannabis."

FAIR TEST?: The roadside test used to detect drug drivers, picking up cannabis and methamphetamine. Helen Spelitis

Mr Ricketts explained that this lack of research into levels of impairment has led the government to taking a strict no tolerance policy, meaning any trace of THC warrants a conviction of the driver.

"You are not guilty of being drug affected whilst driving a car, you are guilty of failing the test and showing a trace of the drug in your system," he said.

"That is the essence of the widespread criticism of the law, it claims to be there as a road safety law but it is really just backdoor prohibition of those substances."

Member for Clarence Chris Gulaptis hit back at Mr Ricketts' claims, labelling them as "ludicrous", ensuring the law was in place to save lives.

"I think that is nonsense, bear in mind taking illicit drugs like cannabis is illegal, period," Mr Gulaptis said. "This program is about saving lives pure and simple, and anyone who wants to put a different spin on it than that is ludicrous."

Earlier this week Lismore magistrate David Heilpern found Lismore man Joseph Carrall not guilty of a drug driving offence on the grounds the defendant had "honest and reasonable belief" he did not have a detectable quantity of cannabis in his system.

Mr Carrall had been told on a previous occasion by a police officer conducting a saliva test that if he waited a week before driving there would be no cannabis detectable in his system.

Mr Carrall's defence lawyer, Steve Bolt, said "the second time he was tested, the test proved positive but that was nine days after he said he had last consumed cannabis."

The court accepted that it was a truthful account and found that in that situation, it was a reasonable proposition for him to rely on what the officer had told him previously.

The acquittal of Mr Carrall has thrown open a debate on the issue with experts believing the tests to be unreliable and many unsure of what the true time it takes for cannabis to leave the system.

Centre For Road Safety executive director Bernard Carlon said he believes the testing can pick up residual cannabis up to 12 hours after it has been consumed.

In his judgment Mr Heilpern said: "That gauntlet is apparently part of the mystery and uncertainty-by-design of the current testing regime."