Medicinal cannabis user worried about new drug driving laws
Saturday, 5 April 2025
An Invercargill man who uses legally prescribed medicinal cannabis to treat his mental health believes he will return positive drug driving tests despite being unimpaired.
Legislation to allow roadside drug testing passed its final reading in Parliament in March and would come into force in April 2026.
The legislation gave police powers to randomly saliva test drivers at the roadside for drugs likely to include THC [psychoactive ingredient in cannabis], cocaine, ecstasy and methamphetamine.
If drivers test positive in two tests in a row at the roadside they would be immediately banned from driving for 12 hours.
The positive test would then be sent away and laboratory tested, and if that test confirmed drugs at a level indicating recent use that impaired driving, the driver would be fined and issued demerit points.
Jarvis said he was prescribed medicinal cannabis to treat his mental health after being diagnosed with Complex Post Traumatic Stress Disorder pertaining to Oppositional Defiant Disorder traits, stemming from being abused by adults in state care.
He said his previous prescribed medication — benzodiazepines — stupefied him and did not prevent him from waking in the early hours with “panic, terror and flashbacks” stemming from the past abuse.
But since taking prescribed medicinal cannabis in recent years, he had slept through the nights and woken with a clear mind.
The containers he received his medicinal cannabis in specified he could not drive within six hours of taking the product, and he stuck by that, he said.
He was not impaired when he drove after the six hours, he said.
“But now I am really worried. I use it every night for my mental health and cannabis doesn’t leave your system for days. So I am going to test positive with these tests every time I get pulled up, despite waiting six hours before driving and being unimpaired.”
Jarvis, who was awarded a King’s Service Medal in the 2025 New Year Honours list for his services to survivors of abuse in care, believed many people receiving prescribed medicinal cannabis for legitimate health issues would have the same concerns.
“There’s got to be better ways of dealing with drug driving as opposed to attacking patients such as myself who are abiding by the parameters of our medication.”
Transport minister Chris Bishop said the roadside tests would target recent, as opposed to historical, drug use.
A defence would be available for drivers to dispute an infringement notice if they proved they had a current prescription for the drug and had followed their doctors instructions to not drive within a specified time of consuming the drug.
They would, however, still be prohibited from driving for 12 hours if they had two positive tests in a row after being pulled over, in order to address any immediate road safety concerns.
A Ministry of Transport spokesperson said it was important drivers were not impaired and at risk of causing harm on the roads, whether prescribed a medication or not.
Cannabis Clinic medical director Dr Will Parkyn said studies showed that oral saliva tests for THC could be positive for 72 hours in regular users.
His concern was that patients who were using their cannabis medication as per their doctors instructions, and were driving unimpaired, would face penalties.
“This is because, with THC the test results can be positive for much longer than someone is potentially impaired.”
Studies showed regular users of THC built a tolerance to the impairment associated with its use, “so they could well have a positive result, despite no impairment”.
On one hand, he was pleased a medical defence was available for medicinal cannabis users.
“This means if a patient tests positive for residual THC but has been using their products as per our doctors' advice, they will have a medical defence.
“Unfortunately however, if they test positive at the roadside they will still have to stand down from driving for 12 hours, whether they are impaired or not.”
Using Jarvis as an example, Parkyn said the Invercargill man could take his prescribed medication at night, sleep well, and wake up fresh and unimpaired, “only to be pulled over [while driving], test positive for residual THC and face penalties, including the mandatory 12 hours stand-down from driving”.
Data from the New Zealand Drugs Trends Survey showed that in 2024, 160,000 medicinal cannabis prescriptions were written for Kiwis, he said.
A police spokesperson said police already undertook impaired driver testing for alcohol and drugs.
“The further addition of roadside drug driver testing to our existing practices is about ensuring that we have the tools to deter and detect those drivers that are over a level that is considered unsafe to drive.”