Roadside drug testing and medicinal cannabis: what patients need to know

September 9, 2026

Random roadside saliva testing is now operating across New Zealand. If you are prescribed cannabis and you drive, this is the law change that matters most to you. Here is what it does, what your prescription is and is not worth, and what happens if you test positive.

What changed

The Land Transport (Drug Driving) Amendment Act 2025 came into force on 15 December 2025. It lets Police stop any vehicle, anywhere, at any time and screen the driver's saliva for four drugs: THC, methamphetamine, MDMA and cocaine. No suspicion of impairment is required. It works like random breath testing.

Testing began in the Wellington region on 15 December 2025, scaled up from April 2026, and has since expanded nationwide.

It still will not be as universal as breath testing

The official line at launch was that drivers can expect to be tested anytime, anywhere. That is true as a matter of law. As a matter of operations, the practical constraints have not gone away.

An oral fluid test takes several minutes per driver, against roughly twenty seconds for a breath test, and each test carries a real per-unit cost to the government, reported at up to around $45. You cannot run a drug checkpoint the way you run a booze bus.

The early numbers bear that out. In roughly the first five months of testing in the Wellington region, around 300 drivers were tested and seven infringement notices issued. Compare that with a single four-day operation in New South Wales, which put through about 9,000 drug tests. The volumes are not remotely comparable.

The reasonable expectation, then, is targeted testing rather than blanket testing: at checkpoints, after crashes, where an officer already suspects impairment, or as part of an operation focused on dangerous driving. That is not a guarantee, and it is not a reason to plan your driving around not being caught. It is context for how likely you are to meet one.

How a stop actually works

An officer wipes a testing pad along your tongue. The device used is the Securetec DrugWipe 3 S.
If that first screen is positive, you take a second roadside screening test.
If both are positive, you are prohibited from driving for 12 hours. This happens at the roadside, on the spot.
A saliva sample is also collected and sent to a laboratory, where it is analysed for 25 substances.
An infringement notice is only issued if the laboratory result comes back positive.

Refusing the test, or leaving before the result is ready, gets you an infringement notice and the 12-hour ban anyway.

A lower-level infringement tier now exists

This is the part that gets lost. Before this law, having THC in your system was dealt with as a criminal matter and the legitimacy of prescribed cannabis was not recognised at all. Now there is an infringement pathway sitting below the criminal offences, and prescribed use is recognised in statute.

Police have published the infringement penalties: $200 and 50 demerit points where one qualifying drug is detected, $400 and 75 demerit points where two or more are detected, alongside the 12-hour driving prohibition. An infringement is not a conviction and does not carry automatic disqualification.

The criminal penalties still exist above that, for evidential blood results over the criminal limits and for driving while impaired.

Worth doing the maths on the demerits, though. A licence is suspended at 100 points, so a single $400 infringement puts you three quarters of the way there.

What your prescription is worth

This is the part patients most often get wrong, so it is worth being precise.

At the roadside, your prescription does nothing. It is not an exemption. It will not stop the test, will not change a positive result, and will not save you from the 12-hour driving ban. Police have been explicit about this.

Afterwards, it may well save you the fine. Section 64(1AB) of the Land Transport Act gives a medical defence to the oral fluid infringement offences. You qualify if you have a current, valid prescription for the drug written by a health practitioner, and you have complied with any instructions from your prescriber or the manufacturer about driving and about mixing the medicine with alcohol or other medicines.

As Police Superintendent Steve Greally put it when the law came in, the medical defence means people with a legitimate reason for the drug being in their system can say so, and "in some cases will have their infringement waived".

Note the second half of the statutory test. The defence is not just "I have a prescription". It is "I have a prescription and I followed what I was told about driving". Which is a good reason to have that conversation with your prescriber and to know what you were told.

How to apply for the medical defence

You apply to Police after you receive the infringement notice. There is an online form: Medical Defence Application Form, Impaired Driving (Drug Driving), Section 64 Land Transport Act 1998. A downloadable PDF version is also available on the Police medical defence page.

You will need your current prescription and a copy of the label from the container the medicine was dispensed in.

Two traps worth knowing about, both stated on the form itself:

Police cannot consider a medical defence for a notice you have already paid.
They also cannot consider it once the notice has been transferred to the Fines Collection Unit of the Ministry of Justice.

So do not pay it to make it go away, and do not sit on it. Apply promptly.

Practical suggestion: keep your dispensing label, or a photo of it, and a copy of your prescription somewhere you can find them, since the label goes with the medicine and the medicine may not be where you are.

Presence is not impairment

A saliva test tells you a substance is present above a set threshold. It does not tell you whether the person is impaired. This is not a fringe view: the AS/NZS standard Police use to set oral fluid detection thresholds says itself that oral fluid results should be related to recent exposure rather than impairment.

Estimates of how long THC stays detectable in saliva vary widely, commonly cited as somewhere around 8 to 12 hours after use and longer for frequent or heavy users. Detection can therefore outlast any effect by a long way. Police themselves say they cannot advise how long after taking a substance it is safe to drive, because metabolism varies too much between individuals, and they refer people to their prescriber.

Police scientific advisers have also said that people taking cannabis-based medication exactly as prescribed are unlikely to return a positive roadside screen. Whether that holds up for daily patients on higher doses is something the next couple of years of enforcement will answer. How these tests are applied and interpreted in practice, and in court, will become clearer over time, particularly where impairment is disputed and particularly around the practical application of the 12-hour prohibition.

Where this leaves patients

Honestly: in an uncomfortable position, and one we think deserves more attention than it gets. The law recognises the legitimacy of prescribed cannabis, which is real progress on where things stood a few years ago. But the recognition arrives after the stop, not during it. A patient who is not impaired, has done nothing wrong, and is taking their medicine exactly as directed can still lose twelve hours of driving and have to go through a paperwork process to get out of a fine.

The 12-hour ban is the sharpest edge of it. For someone with a job to get to, kids to collect, or a rural address, it is not a minor inconvenience.

What to actually do

Talk to your prescriber about timing, dosing and driving, and write down what they tell you. The medical defence depends on you having followed it.
Leave a real gap between using your medicine and driving. Ask your prescriber what gap suits your product and dose.
Keep your documentation accessible. Current prescription, dispensing label, both easy to lay hands on. A photo on your phone is a good start.
Do not pay the infringement if you intend to apply for the medical defence. Apply first.
If you feel impaired, do not drive. If you are unsure, wait longer, get a ride, or plan your dosing around when you need to drive. The medical defence covers presence. It does not cover impairment, and driving impaired is an offence with a prescription or without one.

Where to read the source material

Police publish the infringement penalties and the medical defence process on their own site, the Ministry of Transport has a page on the 2025 Act, and the NZ Drug Foundation keeps a detailed and regularly updated explainer aimed at people who use drugs rather than at enforcement agencies. Those three are the ones we would send a member to.

This is general information, not legal advice, and the rollout is still evolving. Check the current position with Police or the Ministry of Transport before you rely on anything here. If you are a patient with questions about your own situation, talk to your prescriber.