Why police don't test for prescription drugs

Whenever police or media mention roadside drug testing, a wave of frustration inevitably follows in the comments. You’ve seen them. Maybe you’ve written one. They usually look something like this:

The logic seems simple: If roadside drug testing is about safety, why are people taking prescription meds — like Valium, Tramadol, or even ADHD stimulants — allowed to drive without scrutiny, while cannabis and meth users are caught out instantly?

Let’s unpack this.

What Actually Is Tested for?

Roadside drug testing in Australia roughly follows the AS/NZS 4760:2019 standard, which outlines drugs detectable in oral fluid (saliva). It focuses on substances most likely to impair driving and that can be reliably detected in a roadside setting.

The standard includes:

• Amphetamine-type substances: e.g., methamphetamine (ice), MDMA (ecstasy), amphetamine

• Cocaine

• Opioids: e.g., heroin, morphine, codeine

• Oxycodone: given its rising misuse, it's tested as a separate class

• THC (Cannabis)

While other substances can be tested in a lab — including benzodiazepines, alcohol, and designer drugs like K2 — they are not part of routine screening.

The Roadside Tech Has Limits

State police forces use a German made device called the DrugWipe — either the DrugWipe II (Methamphetamine, THC) or DrugWipe III (Methamphetamine, Cocaine, THC) depending on the jurisdiction. These are not used in Australian workplaces because they don’t meet the full Australian Standard. However, laboratory confirmation (usually conducted by NATA-accredited facilities) does meet the standard and is required before you end up in court.

But here’s the catch: the DrugWipe can only test for a handful of drugs, and each additional “panel” costs money, time, and comes with accuracy trade-offs. So police are prioritising substances:

• That have no legitimate reason to be in your system (Stoners, THC being prescribed doesn't mean you can drive with it in your system. Even dodgy online weed dispensaries make that clear to you before they sell you THC products)

• That impair driving

• That can be reliably detected in oral fluid at roadside

So Why Not Test for...

Prescription Amphetamines? (e.g. ADHD meds like dexamphetamine)

These drugs are prescribed and often improve cognitive performance and reaction time in people with ADHD. They don’t show up on the Methamphetamine (MET) test — the one used roadside. So unless someone is abusing street meth, they won’t be caught. That’s intentional. We don’t want people with ADHD going off their meds out of fear of a roadside test.

Opioids? (e.g. painkillers, codeine)

Technically, it’s illegal to drive while impaired, regardless of what drug causes the impairment (R v Liddicoat is a good case to look into for people being busted for driving with 'legal' drugs like opioids and benzo's in their system and then having accidents). But testing oral fluid for opioids is problematic. For example:

• A person might take cold/flu meds with codeine, feel fine, but still test positive.

• Another might be high on oxycodone but pass the test because of poor detection in oral fluid.

It’s messy — so police just don't bother testing for it as it would clog up the system.

Benzodiazepines? (e.g. Valium, Temazepam)

Benzos are a massive issue for impaired driving. But here’s the problem: They have long half-lives in the body, but short detection windows in saliva — as little as 4 hours. So someone could take a Valium at 2 a.m., drive at 8 a.m. still impaired, and test negative. That’s a terrible use of a test panel.

But... Isn’t This Unfair?

Yes — but it’s also the best available compromise.

Police aren’t looking to detect all drug use. They’re trying to detect recent, impairing drug use that can be verified quickly, reliably, and affordably on the roadside — and that makes the roads safer.

If you want a full-spectrum drug test like you’d see in a mining or transport workplace? That requires urine, a full lab panel, and time — which is simply not practical when pulling someone over on the M1. Also, urine presents separate problems as it wouldn't be showing recent use, it could be showing anything from 2 days to 9 months ago.

Takeaway

The frustration is real, and the Facebook commenters aren’t wrong to raise the question. But the answer isn’t as simple as “just test for everything.” Roadside drug testing is a blunt tool — not a diagnostic one. It’s designed for speed, deterrence, and clear court outcomes — not nuance.

Until the tech improves or the law changes, that's why your painkiller meds or Mum’s sleeping tablets aren’t showing up on the roadside test — even if they arguably should.