Roadside drug testing – an explainer for people who use drugs

There has been some confusion around the new rollout of roadside drug testing in Aotearoa. This regime has been marketed as a measure to reduce the incidence of people driving whilst impaired from drugs other than alcohol. However, this is clearly a charade with there being no evidence that such results will occur, and the regime being setup in a way which clearly just prohibits driving by anyone who has recently used drugs – not just those who are impaired. This new testing has led to some confusion as it all rests around two distinct pieces of legislation, enacted within a few years of each other, with a similar name, and a similar purpose. So, before we get into the testing itself, lets look over the legislation and the history of the regime that led us here (just scroll down for helpful tips): 

1. In 2022, Land Transport (Drug Driving) Amendment Act 2022 (2022 No 5) passed (2022 Drug Driving Law). This amended the Land Transport Act 1988 and is incorporated into it. This law was the first attempt to enable roadside drug testing however, this law required that testing devices met highly accurate criteria. No devices could be found that were accurate enough to be legal and thus, roadside drug testing did not occur under this amendment.

2. However, in March 2025, a new amendment act passed: the Land Transport (Drug Driving) Amendment Act 2025 (2025 Drug Driving Law). What has led to confusion is that this new version is not yet incorporated into the Land Transport Act 1988 - that is, if you go and look at the Land Transport Act 1988, it still shows you the 2022 Drug Driving Law. This is what a lot of information online is based on – so make sure to check the date of any articles or information that you read! This newer amendment was passed to enable the use of less accurate testing devices, and this is the law under which this new roadside drug testing regime is legislated.

3. The 2025 Drug Driving Law doesn’t come into force until 15 December 2025, at which stage it should be reflected in the Land Transport Act 1988. While this may make understanding of the law a bit simpler, legislation is still complex and thus, we have done our best to clarify the key points for people who use drugs in Aotearoa (recreational, medical, or otherwise)

What are these tests? Any police officer may require any driver of a vehicle to complete a roadside drug test (the police use the term ‘oral screening test’ – these are the new tests) or a compulsory impairment test (the old mechanism for detecting impairment). Whilst the compulsory impairment test tests for impairment directly and has some basis in scientific evidence, the new roadside drug tests only test for recent drug use. It is important to note here that whilst this law is being pushed as a measure to reduce drug impaired driving, the wording of the legislation explicitly states that it is driving after using drugs recently that is being penalised, not driving whilst impaired by drugs. ‘Recently’ here can mean up to a day or two ago, not just a few hours. Make no mistakes, this is a law designed to attack the rights of people who use drugs to freedom of movement and nothing else. There is no evidence that this law will reduce drug-impaired driving, it does not specifically target drug-impaired driving, the tests used are not even able to determine impairment, and the statistics used to justify this law conflate correlation with causation in a dishonest fashion.

These new tests consist of a mouth swab and the collection of a saliva sample. The police officer will use your sample to conduct a test at the roadside which will determine whether THC (the main psychoactive component of cannabis), cocaine, MDMA (aka ecstasy or pingers), or methamphetamine is present. If the first test is positive (they find one of the four drugs), the sample will be sent to a lab for further testing, and the officer will conduct a second test. Two positive tests will automatically lead to a 12-hour ban on driving and you will be stranded on the roadside. If the lab test identifies certain amounts of one of the drugs of interest (they use the term ‘qualifying drug’), then you will be issued with an infringement notice (like a speeding fine). The lab-based test will look for a much larger list of drugs than just the four tested at the roadside. Whilst the list of drugs that will be tested for through lab testing have not yet been released, it is likely to be a similar list to those already prescribed in the Land Transport Act for blood tests (Schedule 5, Land Transport Act 1988). We do not yet know how long the lab tests will take however, it is likely to be many weeks, if not months before people are informed of the results.

What are my options if I am stopped? If you are stopped and asked to complete an oral screening test, you are allowed to refuse. Refusal will however result in an instant 12 hour driving ban, a $400 fine, and 75 demerits (100 demerits results in a 3-month loss of license). Refusal of a test receives the same punishment as being identified with multiple drugs in your system. If you opt to do the test, the officer will do the first test. If this test is negative, you are free to go. Otherwise, if the test is positive, the officer will send a sample away to a lab and begin another test. If the second test is positive, then you will receive an instant 12 hour driving ban but no infringement (yet). The infringement will depend on whether the lab test identifies any of the drugs of interest.  An officer may require a person to do a compulsory impairment test only up to the second oral test. If an officer decides to do a compulsory impairment test instead of the final oral test, they cannot complete the oral test and thus, this removes the potential of an infringement notice or a 12-hour driving ban for the person. However, failing a compulsory impairment test does open the potential for harsher penalties than failing a roadside drug test, so this needs to be considered. Unlike the drug tests however, these tests can actually determine impairment if done correctly and thus, this option may be preferable. Unfortunately, the law simply states the officers may do this and there is no requirement that they offer the compulsory impairment test.

What influences the amounts of drugs in my system when driving? How can I reduce this? The amounts of drugs in a person’s saliva or blood are highly variable from individual to individual due to genetic variation. The amount of a drug in someone’s system may also not always be the same between different drug using occasions, where the same amount is consumed, due to environmental factors – this is why you may sometimes consume the exact same dose of a substance on two different occasions but feel very different effects. Many environmental factors can alter drug metabolism including how much you have eaten that day as well as what you have eaten. Many drugs, foods, and drinks can alter the metabolism of other drugs as well. This is particularly true for drugs such as Ozempic which speed up metabolism or grapefruit juice which can slow down metabolism of some substances.

Generally, blood and saliva levels of a drug will increase after ingestion as the substance is metabolised to a peak as effects are felt. After this, levels begin to decrease as the substance is excreted through the urine over time. Once the effects of the substance have subsided, the drug, and its metabolites, may exist in the body for a while longer – this period can be many hours or days and is the key problem with roadside drug testing. During this period, people are no longer under the influence of the consumed substances however, they are still likely to fail a drug test, whether that is a roadside test, or lab-based saliva or blood test. For people who are no longer impaired by their drug use and wish to ensure that they are not wrongfully charged by a roadside drug test, shortening this period and not driving until this period is over is essential. While the architects of this program would have you believe that they have set limits on the lab tests to ensure that people with low levels of drugs in their system are not penalised – the limits suggested by New Zealand’s current blood testing legislation as well as the limits typically used overseas suggest that more than half the people prosecuted for having drugs in their system will not be impaired. Our submission on this bill from last year has some good numbers on that if you’re interested.

Thankfully, each of the four drugs that will be tested for at the roadside, as well as many tested for in the lab, are used medically and thus, their metabolism and excretion from the body have been researched extensively. From this research we know that more acidic urine can speed up the excretion of some stimulant drugs such as cocaine, MDMA, and a variety of amphetamines, including methamphetamine. Flushing your system with something that will make your urine more acidic may be helpful here. However, it is important to note that excessive consumption of certain supplements as well as having more acidic urine can have its own health risks so be sure to do your research before relying on such methods. There is some evidence that cranberry juice or vitamin c supplements may make your urine more acidic and thus, enable faster drug excretion however, this research is limited and there have been some conflicting results. Note that despite being acidic, the metabolism of orange juice, lemon juice, and grapefruit juice have the opposite effect and thus, are not useful here.

In addition to the above information, the method of ingestion will likely influence how quickly drugs are metabolised and excreted from the system. Methods that result in the drug effects having a shorter duration will likely also result in drugs being out of your system sooner. Additionally, quantity and consistency of use will also increase the chance of failing a test. Using a lower dose and less often will reduce the amount of time that you spend with qualifying drugs in your system.

How is cannabis different to other drugs? Whilst simply clearing the drugs as much as possible from your system is the best method for reducing the chance of triggering a positive test for most drugs, the chemical nature of THC makes it quite distinct. THC is well known for sticking around in the body for much longer than other drugs – this has been a problem for people in workplace drug testing settings for years. This same feature of THC metabolism plays a role with roadside drug testing. Whilst clearing as much drug as possible is the best way to reduce saliva levels of most stimulant drugs, THC sticks around and saliva levels are more dictated by the amount of THC that has been present in the mouth. Thus, the form of THC and the way it is consumed can significantly affect how much THC contacts the mouth and how long it remains in saliva. Based on this, evidence suggests that the best way to minimise the amount of THC in saliva is to consume edibles. Tar and other compounds can increase the time the THC sticks around in the mouth and thus, vaping, smoking, and smoking mixed with tobacco will lead to THC sticking around longer in the mouth and thus, the risk of failing a test increasing. The below image shows a rough estimate of the risk of THC sticking around in the mouth and triggering a positive test based on the method of ingestion, with smoked tobacco combinations being the highest risk and edibles contained within capsules to be the least.

Lower risk

Capsules

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Edibles

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Vaped cannabis

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Smoked cannabis

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Cannabis & tobacco

Higher risk

 Whilst not completely foolproof, the best method ideally would be to consume edible cannabis extracts in capsule form, limiting exposure to saliva as much as possible.

The dry mouth experienced by cannabis smoking also reduces salivation and thus, makes the concentration of drugs in saliva much more potent. Staying hydrated can mitigate this issue slightly. In this same vein, consuming substances which increase salivation such as citric acid (sherbet) has the potential to reduce the chance of failing a test for a short period. Such effects are quickly diminished once excess saliva is swallowed and saliva levels return to normal.

How does this differ if you use drugs for medical reasons? Even if you do not use illicit drugs, this legislation may still impact you. People who use medicinal cannabis will still likely fail the roadside tests and face the 12-hour driving disqualification, even if using their medicine in accordance with their doctors’ directions. While a medical defence exists in the legislation, police have stated that medical patients cannot prove their medical status at the roadside and thus, must apply for the medical defence after the fact. Thus, it must be assumed that all medical consumers are at risk of a 12-hour driving ban whenever they drive.

Whilst the roadside tests are not likely to pick up any other drugs typically used for medical purposes, they are known to have a high false positive rate. This means that a lab test may be initiated simply because the roadside test gave an incorrect result. If this occurs, a much larger number of substances will be screened for through lab testing. Whilst a notice of which drugs will be screened for through oral fluid has not yet been released, it can be assumed that this it will likely reflect the currently legislated list of drugs for blood samples (Schedule 5, Land Transport Act 1988). This list contains numerous drugs used medically such as methadone, benzodiazepines, and opioid painkillers. In addition, the police have noted that dexamphetamine will result in failing a lab test despite this not being listed in Schedule 5 of the land transport act, suggesting that they intent to screen for a larger number of drugs than previously. It is uncertain at this stage how difficult a medical defence will be however the system reeks of a ‘guilty until proven innocent’ approach.

Where are these tests occurring? Currently the testing is being trialed in Wellington before being rolled out to the rest of the country after summer next year. Despite this, we have heard some unverified reports of police carrying out roadside drug testing in other areas and there is no legal limit on where they can do this. These unverified reports suggest that there are no road block style stops occuring outside of Wellington however, some police officers may have these devices on hand anywhere in the country. Be careful wherever you are and ensure you have measures in place to stay as safe as possible.

Top tips:

• Using smaller amounts of drugs and methods of administration with a shorter duration will result in lower levels of drugs in the system the next day.

• Acidifying your urine may speed up the excretion of stimulant drugs after a big night, lowering the chance of testing positive however there is not enough research for this to be relied upon.

• Only THC, cocaine, MDMA, and methamphetamine are tested for at the roadside. Non methylated amphetamines (e.g. MDA and amphetamine) and other drugs will not be tested at the roadside. When using drugs that are not tested at the roadside, it is important to note that driving with these drugs in your system is still illegal and these drugs may still be picked up in the lab test if false positives or other drugs give a positive result for the initial roadside test.

• Avoid smoking cannabis if you are concerned about passing a roadside test and opt for edibles instead, especially if you use medical cannabis.

• The medical defence only applies if following your doctors’ directions. Smoking medical cannabis is not the way that you are meant to take it and thus, this may prevent the use of the medical defence – ensure that you are using your medical cannabis as directed with a legally approved vaporiser.

• It is advised that people who use drugs have a backpack in their car and a plan to get home if they are stopped for random roadside drug testing. This is particularly important for people who use medicinal cannabis.

• Substances that increase salivation such as citric acid (often in sherbet) may temporarily reduce the chance of failing a test however, such methods are unreliable, and their effects are short lasting.

• Keeping hydrated, well fed, getting enough sleep, good oral hygiene, and waiting a reasonable length of time between consuming drugs and driving is the best way to ensure that you are not going to fail a roadside test and that as much of the consumed drugs are out of your system.

• Apps exist that are designed to quickly test for impairment before driving such as ‘DRUID’. These may be useful and are currently in use by several medicinal cannabis consumers. It is unlikely that such an app showing you to be unimpaired will have any legal benefit if you are caught by the police however, it is a good way to ensure that you are driving safely.

Further reading:

• The Police have put out a document outlining what this means for people with ADHD, here.

• An up to date article from the New Zealand Drug Foundation which explains this well: article.

• The polices webpage on roadside drug testing, here.  Up until the legislation was enacted on the 15^th of December, this page contained outdated information that was confusing many people. This has now been updated. This page frequently conflates the presence of drugs with impairment in a dishonest and un-scientific fashion however, it does state the processes involved clearly.

• If you’re a pharmacology nerd and into numbers, the cut-off values for failing a lab test are here.

SSDP would like to thank Dr Lee Miles for his help with some of the research in this article.