Mobile Drug Testing (MDT) in Australia: How Roadside Saliva Tests Actually Work
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The process, from "please pull over" to a lab result
Mobile drug testing (MDT) looks casual — a swab, a few minutes — but it's a multi-stage legal process, and understanding it helps you stay calm and make fewer mistakes. The broad sequence is similar nationwide; details vary by state.
1. The stop. Police can stop you at a static testing site or anywhere as a mobile patrol. You must stop and comply with a lawful direction to undergo testing — refusing an oral fluid test is itself a serious offence in every jurisdiction, usually treated at least as severely as a positive result.
2. The first screening test. A saliva swab, typically scraped along the tongue. It screens for THC, methylamphetamine and MDMA — and in some states cocaine. It does not test for impairment, dose, or when you took your medication. CBD is not a target substance.
3. The second test (if the first is positive). You'll be directed to a testing bus or roadside unit for a second oral fluid sample analysed on more sensitive equipment. Many first-positives end here when the second test disagrees.
4. The driving ban. After a confirmed positive screening you will be banned from driving for a period — commonly 24 hours. Driving within the ban is a separate offence. Arrange transport; do not move the car "just around the corner."
5. Laboratory confirmation. Your sample goes to a lab. The roadside result is indicative only — the laboratory analysis is the evidence. Charges typically follow only after lab confirmation, which can take weeks.
6. Paperwork. Depending on your state and the offence, you may receive an infringement/penalty notice or a notice to attend court. Nothing arriving for a while does not mean the matter is over.
What you must do, and what you may decline
- You must provide the oral fluid sample when lawfully directed, and provide your licence and identifying details.
- You are not required to answer questions about what you've taken, when, or your prescription at the roadside. Being polite and calm is smart; volunteering a timeline of your medication use is evidence you can't take back. "I'd prefer to get advice before answering questions" is a complete sentence.
- If police suspect impairment (not just presence), a different and more serious process can follow — including a driving assessment or blood test. Comply with lawful directions; get advice early.
Why patients on stable doses still test positive
Roadside tests detect the presence of THC in oral fluid, which correlates poorly with both impairment and time since dose. Regular patients can test positive many hours — sometimes days — after their last dose, long after any impairing effect has passed. That mismatch is the core of the reform debate, but under current law in most states, detection is enough. See: how long does THC stay detectable?
Practical notes for prescribed patients
- Keep your prescription details and dispensing records accessible (photo on your phone is fine). In most states this won't prevent a charge, but it matters later — for court, for Victoria's licence discretion, and under NSW's proposed scheme.
- Note everything immediately after any stop that goes badly: time, location, what was said, when you last dosed. Contemporaneous notes are gold for your lawyer.
- Never drive impaired. Every defence, discretion and proposed scheme in the country evaporates if you're impaired — and it's dangerous.