New research shows how long it takes for cannabis degradation to subside

New research has shown for the first time how long cannabis users are likely to be affected and when it may be safe for them to drive.

The findings, researchers and advocates say, reinforce the case for changes in drug driving laws across much of Australia.

Researchers at the Lambert Initiative for Cannabinoid Therapeutics at the University of Sydney found that users had a disability for three to 10 hours after taking moderate to high doses of the intoxicating component of cannabis, tetrahydrocannabinol (THC).

THC can be detected in the body weeks after cannabis use, meaning users could be fined and forfeited their license, despite not being affected by the drug.

The research, published in Neuroscience & Behavioral Reviews, analyzed 80 scientific studies on the effect of THC on driving performance, conducted over the past 20 years.

It found that the exact level of deterioration depended on the dose, whether the THC was taken orally or inhaled and how often the person used the drug, among other factors.

“Our analysis indicates that a disturbance can last up to 10 hours when high doses of THC are taken orally,” said study lead researcher Danielle McCartney.

“However, a more typical attenuation duration is four hours when lower doses of THC are consumed via smoking or vaporization and simpler tasks are performed.”

The study also found that regular cannabis users were less affected by THC than those who used cannabis occasionally.

Dr. McCartney said people can be disabled for six or seven hours if higher doses of THC are inhaled and complex tasks, such as driving, are assessed.

Her research is the first comprehensive meta-analysis to establish a disability timeframe.

“Our evidence should hopefully help people make informed decisions and policymakers to make evidence-based policies and tell people how long to wait before driving,” she said.

The Therapeutic Goods Administration (TGA) has approved 100,000 prescriptions for medicinal cannabis in Australia.

Lambert Initiative Academic Director Iain McGregor said medical cannabis users were particularly interested in knowing when it was safe for them to drive, despite the law being clear on the matter.

“You get a tremendous amount of a prescription drug in people who are told, ‘You can’t drive a car at all, you can’t even have one molecule of THC in your system,’ which, you know, is just ridiculous,” said Professor McGregor .

“THC can be detected in the body weeks after cannabis use, while it is clear that the duration of the disorder is much shorter. Our legal frameworks should probably catch up.”

Former magistrate David Heilpern said the investigation showed that roadside drug testing laws needed to be changed.

Mr. Heilpern took early retirement, in part because of his frustration at seeing so many medical cannabis patients lose their driver’s license and sometimes their livelihood after being caught driving with small amounts of THC in their system.

“We had a situation where people were taking their medications as prescribed, they were not driving in an unfavorable way and yet they lost their driver’s license, were fined and given a criminal record,” he said.

‘I started driving home from work and thought, I just can’t do this.

Mr. Heilpern said that cannabis is the only prescription drug in Australia that you cannot drive with even a detectable level.

He is part of the Cannabis Law Reform Alliance, which advocates for changes to state laws and provides medical cannabis users with a defense if they test positive on a roadside drug test.

The defense already exists in Tasmania and there are bills in parliament in Victoria and South Australia. NSW’s parliament rejected a bill on the matter in October.

“In NSW we already have that law as it applies to morphine,” said Mr. Heilpern.

“If you have detectable morphine levels in your system and you can show that you have a prescription for it, then you have a defense.

“All we have to do is do that for cannabis. It’s a very simple change and it solves the problem.”

Gino Vambaca, co-founder of Harm Reduction Australia, said Australian laws punish people for past drug use, not unsafe driving.

“It’s not a road safety campaign anymore, it’s a search and punishment campaign,” he said.

“We don’t condone people who use drugs and drive, but what we’re saying is that the police are making no attempt to even measure impairment.

“To people who use medical cannabis, we should say, ‘Do you want to drive or do you want pain relief, because you can’t do both.’

“And that’s a terrible choice they have to make.”