DrugWipe Roadside Drug Tests: Why Police Get Them Wrong

And How This Can Be Used in a Drug Driving Defence

Roadside DrugWipe tests are widely used by police to identify drivers suspected of drug driving. They appear simple, but these devices are highly sensitive, easily compromised, and legally significant in ways most drivers,  and many police officers (and defence solicitors), do not appreciate.

Roadside drug driving procedure is often overlooked as inconsequential due to the years of case law in drink driving cases. However, there are some material differences with drug driving cases due to the conditions required for an evidential blood sample to be taken in drug driving investigations.

A DrugWipe test is not only an indicator of possible drug presence; it is one of two legal triggers that opens the gateway allowing police to demand a blood sample.

When the test is not performed correctly, that legal gateway may be open to challenge as it may be possible to argue that the police had no lawful basis to require a blood specimen, in which case, a drug‑driving charge may fail entirely.

This article explains:

• how DrugWipe tests work
• the errors officers commonly make
• the scientific problems with THC and BZE/Cocaine (the only substances capable of being detected on a DrugWipe)
• the statutory requirements under Section 7(3)
• how an incorrect DrugWipe or missing nurse’s opinion can form a complete defence

What Is a DrugWipe Test?

A DrugWipe is a type‑approved preliminary drug test used at the roadside or in custody. It is a lateral flow device (like a Covid test), designed to detect drugs such as:

• Cannabis (THC)
• Cocaine and BZE (a cocaine metabolite)

Saliva is collected on the blue sampling pad.

Before the test can even begin, the red pads must turn yellow confirming adequate saliva has been collected.

Importantly:

• A DrugWipe is not a proof‑of‑guilt device and cannot be used as evidence of being over the drug drive limit.
• It is merely a screening tool.
• Its reliability depends entirely on the officer following the manufacturer’s instructions exactly.

Why Procedure Is Everything

DrugWipe results are reliable only when the instructions are followed precisely.  The manufacturer explicitly warns that incorrect use means the result should not be relied upon. This is no secret, it is clearly displayed on the leaflet provided by the manufacturer.

This is why, in legal terms, the procedure becomes evidence. If the procedure is flawed, the result is flawed and the legal basis for arrest or blood testing may collapse.

The Most Common DrugWipe Mistakes Officers Make

1. The 10‑Minute Rule Ignored

Drivers must not eat, drink, smoke, vape, chew gum or use mouth spray for 10 minutes prior to sampling. However, officers frequently test drivers immediately after:

• drinking water
• vaping
• using mints/sprays

These interfere with saliva flow and can invalidate the test.

2. Incorrect Saliva Sampling

Manufacturer instructions prohibit:

• touching the sampling pads
• collecting insufficient saliva
• proceeding when pads do not turn yellow

If the pads remain red, the test must be repeated. Often, it isn’t.

3. Device Not Properly Checked

Officers should check:

• packaging integrity
• expiry date
• “unused device” control indicators

These checks are often missing, undocumented, or not shown on body‑worn footage.

4. Timing Mistakes – The Most Frequent Error

DrugWipe results must be read at 8 minutes after activation.

Frequent timing faults include:

• guessing the time
• no timer used
• reading too early
• reading too late
• relying on an incorrect “15‑minute window”

Incorrect timing means the test is not compliant with the instructions or type‑approval requirements.

5. Mishandling the Device

The test must lie flat.

Officers often:

• shake it
• hold it vertically
• tilt it
• move it around while the fluid flows

Because DrugWipe relies on capillary action, movement can distort how the liquid reaches the test and control lines.

6. Misreading Faint Lines

Manufacturers state that any red test line, even faint, indicates a positive.

Errors include:

• treating faint lines as invalid
• wrongly assuming faint means negative
• failing to follow the interpretation guide

7. Relying on Invalid Tests

If control lines do not appear, the test is invalid and must be repeated. Yet invalid tests are frequently used to justify arrest.

THC and Cannabis: Why Results Don’t Always Mean Impairment

The legal limit for THC in blood is extremely low; 2 µg/L. This means:

• THC can be detected long after any impairment has passed
• drivers who feel completely normal can exceed the limit
• residual levels can persist for many hours or days

This creates a situation where drivers are prosecuted not for intoxication, but for leftover traces.

When a flawed DrugWipe triggers the arrest, the fairness of the whole process becomes questionable.

Cocaine & BZE: The Unfair Reality

BZE (benzoylecgonine) is not psychoactive. It is simply a metabolite created when the body breaks down cocaine.

Key points:

• BZE stays in the system far longer than cocaine
• levels can rise even after cocaine has left the body
• a person can exceed the BZE limit with no impairment at all

Legal limits:

• Cocaine: 10 µg/L
• BZE: 50 µg/L

This means:

• a driver may test positive due to past use
• they may be perfectly sober
• yet still be charged

When the gateway to blood testing is flawed, defending such cases becomes even more compelling.

The Statutory Gateway: Section 7(3)(bc) – The Legal Significance of the DrugWipe

Under Section 7(3) of the Road Traffic Act 1988, police can only require a blood or urine sample at a police station if very specific conditions are met.

For most drug‑driving cases, police rely on:

Section 7(3)(bc)

A blood/urine requirement at a police station is only lawful if:

“as a result of the administration of a preliminary drug test, the constable has reasonable cause to believe the person has a drug in his body.”

This means:

✔ A properly administered DrugWipe

✔ producing a valid result

✔ giving reasonable cause

If any part of the DrugWipe procedure was defective:

• the officer did not have lawful grounds to demand a blood sample
• the statutory gateway was never opened
• the requirement for blood was unlawful
• the resulting blood evidence may be excluded
• the charge may fail completely

This is why flawed DrugWipe procedure is not a minor issue; it can be case‑ending.

The Second Gateway: Section 7(3)(c) — Nurse or Doctor’s Opinion

Police also have a separate pathway to lawfully require a blood or urine sample.

Section 7(3)(c)

A blood/urine requirement is lawful if:

a registered medical practitioner or nurse expresses the opinion that the person is under the influence of drugs.

This gateway requires:

• an actual clinical assessment
• a recorded opinion
• given before the blood requirement

It does not require a DrugWipe. However, in practice:

• nurses rarely give a formal “under the influence” opinion
• officers often fail to document the assessment
• custody records may be incomplete
• body‑worn footage may contradict the claimed symptoms

If a nurse’s opinion was not properly obtained or recorded, this gateway cannot be relied on.

Without Either Gateway – The Prosecution is Doomed!

Think of Section 7 as two doors:

Door 1 — DrugWipe (7(3)(bc))

Must be performed correctly to create reasonable cause.

Door 2 — Nurse Opinion (7(3)(c))

Requires a medical professional to state the person appears under the influence.

If neither door was lawfully opened, then:

• the police had no legal power to require blood
• the sample was obtained unlawfully
• the blood result may be inadmissible
• the prosecution may not be able to continue

This is why roadside procedure is often the most important issue in a drug‑driving case.

How a Defence Team Challenges These Issues

Experienced defence practitioners analyse:

• body‑worn video
• roadside timing
• saliva sampling
• pad colour change
• device checks
• handling/positioning
• faint‑line interpretation
• invalid tests
• custody medical notes
• whether a nurse expressed an opinion
• whether Section 7(3) was lawfully activated

Often, even a single procedural error can undermine the entire case.

Frequently Asked Questions

Does a positive DrugWipe mean I’m guilty?
No. It is a screening device only.

Can a faulty DrugWipe be used as reasonable cause?
No. If the test is invalid or performed incorrectly, Section 7(3)(bc) may not be satisfied.

If the police relied only on the DrugWipe, can an error be a complete defence?
Yes. If the DrugWipe was improper, the blood requirement may have been unlawful.

What if the nurse did not give a clear opinion?
Then Section 7(3)(c) may not apply, and the blood requirement may be unlawful.

Conclusion

DrugWipe tests look simple, but they are legally and scientifically complex. Because roadside tests often form the sole basis for demanding a blood sample, any flaw in the procedure can invalidate the police’s legal powers under Section 7.

When neither the DrugWipe gateway nor the nurse‑opinion gateway is properly activated, the blood sample may have been unlawfully required — and the entire case may fall apart.

Drug‑driving allegations involving THC and BZE are already scientifically difficult.

When combined with procedural errors, timing mistakes, or invalid preliminary tests, they frequently provide strong grounds for a defence.

Our track record in this field of specialist motoring law speaks for itself. Between 2021 and 2025 we achieved acquittals in 98% of the drug driving cases we defended. This stat comes from 172 winning cases out of 175 in that period. In many of these cases the DrugWipe procedure featured as a defence argument.