By Helen Poulsen, PHF Science Forensic Toxicologist
The highway has entered a new era. In December 2025, a long-discussed system finally rolled out: oral fluid roadside drug testing. Drivers stopped at checkpoints can now be screened on the spot for recent use of a defined range of drugs: methamphetamine, MDMA, cannabis, and cocaine.
Efforts to improve road safety by reducing drug-impaired driving have been decades in the making. More than 20 years ago, an initial parliamentary bill proposing drug testing for drivers failed to pass, largely because there was little evidence at the time that drug use (outside of alcohol) was a significant issue on New Zealand roads.
That changed with later research. A study conducted by PHF Science examined drug use among drivers killed in road crashes and found substances other than alcohol were, in fact, a contributing factor. The findings helped shift the conversation and laid the groundwork for future policy.
In December 2009, new legislation was introduced. Under these rules, police needed “just cause” to stop a driver, typically based on observed poor driving. If a driver passed a breath alcohol test but still appeared impaired, they could be required to complete a roadside impairment assessment. Failing that assessment meant providing a blood sample for drug testing.
The goal was clear: remove impaired drivers from the road before they could harm themselves or others.
However, the system had limitations. Drivers who were hospitalised after a crash were often unable to complete an impairment test. To address this, lawmakers introduced a provision allowing prosecution if a driver had a Class A controlled drug in their blood, even without direct proof of impairment. In New Zealand, Class A drugs include methamphetamine, cocaine, heroin, and LSD.
A broader harm reduction approach
New Zealand’s approach to road safety hasn’t focused on drugs alone. Over the past decade, a series of legislative changes have aimed to reduce harm on the roads, particularly around alcohol and young drivers.
In 2011, stricter rules were introduced for drivers under 20, lowering the legal blood alcohol limit from 30 mg per 100 mL to zero tolerance. At the same time, the minimum age for a driver licence increased from 15 to 16, and testing requirements became more rigorous. A few years later, in 2015, the legal blood alcohol limit for drivers aged 20 and over was reduced from 80 to 50 mg per 100 mL.
Has it worked?
Measuring the impact of these changes, especially when it comes to drug use, is not straightforward. Reliable, unbiased data can be difficult to obtain. However, one way to assess trends is by comparing drug use among drivers who died in road crashes before and after these changes.
Presence of drugs in fatal New Zealand road accidents
| Drug | Number 2004-2009 | % | Number 2013-2018 | % | |
| No drugs | 515 | 49.2 | 438 | 40.2 | |
| Alcohol | 319 | 30.5 | 291 | 26.7 | |
| Cannabis | 313 | 29.9 | 275 | 25.3 | |
| Stimulants | 54 | 5.2 | 111 | 10.2 | |
| Opioids | 29 | 2.8 | 83 | 7.0 | |
| Sedatives | 39 | 3.7 | 60 | 5.5 | |
| Drivers | 1043 | 89 | 1089 | 80 | |
| Under 20 years | 167 | 12.8 | 102 | 7.4 |
Source: PHF Science Coronial Database
Two similarly sized datasets, with comparable demographics, show some clear patterns. Alcohol and cannabis use among these drivers decreased slightly. However, there was a rise in the presence of other substances, including stimulants, opioids, and sedatives.
There were also encouraging signs. Fatalities among drivers under 20 declined. Moreover, the more recent dataset took six years to collect compared with five for the earlier one, further suggesting an overall reduction in driver deaths.
The data gaps
This data doesn’t tell the whole story: it fails to account for injured drivers, those hospitalised after crashes, or other people affected by these incidents.
Testing practices can also introduce bias. Not all hospitalised drivers are routinely tested for drugs. For example, in 2018, around 700 blood samples from hospitalised drivers were analysed. Of those, 359 (51 per cent) tested positive for cannabis, methamphetamine, and/or MDMA, while cocaine was not detected.
However, even this dataset is skewed. The drivers tested had not exceeded the legal alcohol limit, because when alcohol is present above the limit, additional drug testing is rarely carried out. This makes it more challenging to fully capture the role drugs play in road crashes.
Why change was needed
Over time, it became clear the existing system wasn’t always flagging drug-impaired drivers. The reliance on impairment testing meant many cases went undetected.
In December 2019, the Government agreed to introduce compulsory roadside oral fluid drug testing. Designing this system required careful work, including setting appropriate thresholds for both roadside screening devices and blood drug levels, aligned with established drink-driving impairment measures.
An Independent Expert Panel was formed to guide this process. The panel recommended blood limits for 25 different drugs, based on scientific evidence, international standards, and data from impaired drivers in New Zealand.
The panel didn’t recommend oral fluid thresholds for roadside devices or for laboratory testing, because for many drugs, these are already defined in existing standards, which governs oral fluid testing procedures.
How drug testing works
The roadside test process is quick and non-invasive. Drivers are asked to wipe part of the testing device down the front of their tongue. This part of the device is then placed into a cassette containing a liquid ampoule (a sealed container of fluid), which is broken to carry the saliva sample through the testing strip.
Like a Covid-19 rapid test, the device includes control lines to show it’s working. If drugs are detected at or above the threshold set within the device, additional lines appear, indicating the presence of cannabis, cocaine, methamphetamine, or MDMA. If a driver returns a positive result at the roadside, they must provide a larger oral fluid sample. This is sent for laboratory analysis to confirm if any drugs are present at or above the laboratory cut-off threshold.
While roadside screening focuses on four key drugs, laboratory testing is broader. Samples are analysed for the full range of 25 drugs covered by legal blood limits. Importantly, the oral fluid drug thresholds are different to blood drug limits, and represent recent use of the drug. Furthermore, this testing is targeted, meaning it will not identify other medicinal drugs outside of this defined panel.
One exception is amphetamine-based ADHD medications. While amphetamine-is not tested for at the roadside (no ADHD medications will test positive), if a driver does test positive at the roadside for one of the four drugs, then a laboratory analysis will test for all 25 drugs which includes amphetamine.
Medicinal cannabis
Medicinal cannabis is available in a range of formulations and can be administered in different ways. Because of this variability, patients are typically given tailored advice on how to use their medication safely, particularly in relation to driving.
It’s also important to note that THC thresholds used in both roadside and laboratory testing were established before medicinal cannabis became widely available. These thresholds are designed to detect levels associated with recent recreational use, rather than prescribed medicinal use.
People taking cannabis or amphetamine based medications exactly as prescribed are unlikely to return a positive roadside oral fluid test. Individual responses can vary, and the laboratory confirmation process provides an additional safeguard to ensure accuracy and fairness before any enforcement action is taken.
The ultimate responsibility remains with the driver of a vehicle, and if they are experiencing any impairing effects they should not drive. They should always check with their health practitioner to seek medical advice
Looking ahead
With more widespread testing and a higher likelihood of detection, the hope is that drivers will think twice before getting behind the wheel after using drugs. Ultimately, the goal is simple: reduce harm, save lives, and make New Zealand’s roads safer for everyone.