Medicinal Cannabis Use & Driving in New Zealand Guide
Learn how medicinal cannabis use affects driving in New Zealand. Covers roadside drug testing, legal rights, medical defence and tips.
Education
Apr 23
If you're using medicinal cannabis and wondering how it fits with New Zealand's driving laws, you're not alone. Between prescriptions, road rules, and new drug testing laws coming in by the end of 2025, it can be a lot to wrap your head around. And while the laws are changing fast, the goal remains the same: to keep everyone safe on the road.
Whether you’re a long-time medicinal cannabis patient or just starting treatment, this guide is here to help you understand the key points, clear up confusion, and give you practical tips to stay confident on the road.
If you're using medicinal cannabis under the direction of a healthcare professional and you're not impaired, you can legally drive in New Zealand. However, this situation is complicated by the fact that roadside saliva tests detect the presence of THC—not impairment.
There’s currently no legal threshold for what counts as “too much THC” for a medicinal user. This makes it tricky. To stay safe, many healthcare providers recommend waiting at least 12 hours after taking THC-containing medicinal cannabis before getting behind the wheel.
The key is knowing how your body responds and planning ahead. Everyone processes THC differently.
Starting in late 2025, Police in New Zealand will begin conducting random roadside saliva tests to check for drugs. This works a lot like breath testing for alcohol. You don’t have to be showing signs of impairment—they can test you at random.
These tests are designed to detect a range of substances, including THC (tetrahydrocannabinol), the active compound in cannabis, as well as other drugs such as methamphetamine, MDMA and cocaine. THC can remain in your saliva well after any noticeable effects have worn off. In some cases, it may be present for up to three days, especially for regular medicinal cannabis users. This means that even if you are taking your medication exactly as prescribed, there is still a possibility you might test positive.
The saliva test is quick and simple. If no substances are detected, you can continue on your way. If a substance covered by the test, such as THC, is detected, you will be asked to take a second saliva test on the spot.
For detailed information, see the New Zealand Drug Foundation’s guide here.
If both saliva tests come back positive, you’ll be told not to drive for 12 hours. Your first test sample is then sent to a lab for confirmation.
If the lab test confirms the presence of THC (or other substances), you’ll receive a formal infringement notice. Penalties include:
Keep in mind, this does not mean you were impaired at the time. It simply shows that THC was present in your system. That is an important distinction, especially for medicinal cannabis users.
Yes. If you have been prescribed medicinal cannabis and are using it as directed by your doctor, you can apply for what is known as a medical defence.
However, this defence is not immediate. Even if you show police your prescription at the roadside, the 12 hour stand down still applies if you return two positive saliva tests. You will need to apply for the defence online after receiving the infringement notice.
Some doctors, patients and advocacy groups like the NZ Medical Cannabis Council have expressed concerns about this process. It can create unnecessary stress and confusion for people who are just trying to follow their treatment plan responsibly.
Research into THC and driving continues to grow. A 2025 study by Albrecht and colleagues found that crash risk increases significantly when blood THC levels are above 5 ng/ml. Levels below 1.5 ng/ml, however, didn’t appear to increase risk.
This supports what many experts have said, that the presence of THC does not always mean someone is impaired. People who use medicinal cannabis consistently may have detectable THC in their system without any impact on their driving ability.
The 2021 Independent Expert Panel on Drug Driving also highlighted how difficult it is to set a one-size-fits-all limit, due to individual differences in how THC is absorbed and processed.
Here are some simple and practical ways to protect yourself and others when it comes to driving and using medicinal cannabis,
Following these steps can give you a bit more peace of mind and help you feel prepared, especially if driving is part of your everyday life or something you rely on regularly.
Everyone responds to medicinal cannabis differently. Some people feel completely fine within hours, while others may take longer to feel confident about driving. If you're new to this kind of treatment or adjusting your dosage, it's best to be extra cautious.
And remember, it’s not just about the law. It’s about protecting yourself, your passengers, and others on the road.
1. Will carrying my prescription stop me from getting a fine?
Not at the roadside. Even if you have a valid prescription and are using medicinal cannabis as directed, it will not prevent the 12 hour stand down period if you test positive. However, your prescription can help later when applying for a medical defence to explain your situation and potentially have the penalty reconsidered.
2. Can I refuse a roadside saliva test?
No. You are required by law to comply with roadside drug testing. If you refuse to take the test, you may be issued with an infringement penalty.
3. I tested positive but wasn’t impaired. What now?
First, stay calm. You have the right to request an independent retest of your saliva sample, but this must be done at your own expense. If you are using medicinal cannabis under prescription and following your treatment plan, you can also apply for a medical defence. Be sure to keep copies of your prescription and treatment notes to support your case.
4. How long does THC stay in saliva?
This varies depending on how often you use THC-containing products, your metabolism, and dosage. For occasional users, THC might clear in 12 to 24 hours. For daily or long-term users, it could be detectable for 48 to 72 hours or more. This is why planning ahead and understanding your own usage pattern is important.
5. Is there a safe way to be sure I won’t test positive?
There is no exact science because everyone processes THC differently. However, a commonly recommended approach is to wait at least 12 hours after taking THC-containing medication before driving. If you're unsure how long THC may stay in your system, talk to your doctor. They may help you adjust your treatment timing or dosage if driving is an important part of your daily life.
This article provides general information only and does not replace advice from your doctor, lawyer, or healthcare provider. For help specific to your situation, speak with a qualified professional.
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