Cocaine at a Festival: Could You Still Be Over the Drug-Drive Limit Days Later?

Festival season brings a familiar pattern of enquiries. Someone uses cocaine on the Saturday, feels completely sober by the time they drive home on the Monday, and is then stopped and charged with drug driving. To many people this seems impossible, but it reflects exactly how the law and the science work.

Two different limits, two different substances

Under section 5A of the Road Traffic Act 1988, cocaine is caught by two separate specified limits, and it is important not to confuse them:

• Cocaine itself, the active drug, has a limit of 10 µg/L of blood.
• Benzoylecgonine, the main breakdown product (metabolite) of cocaine, has a limit of 50 µg/L of blood.

A driver can be charged on the strength of the benzoylecgonine reading alone. It does not matter that the parent cocaine has already fallen below its own limit, or is no longer detectable at all.

Why the metabolite lingers

Cocaine is cleared from the body rapidly, often within hours. Benzoylecgonine, however, is produced as the body processes cocaine and is eliminated far more slowly. Depending on the amount used, the pattern of use and the individual’s own metabolism, it can remain detectable in blood for a day or more, and for considerably longer in heavy or repeated users.

The practical consequence is that a person can feel entirely unaffected, be well past any sense of intoxication, and yet still return a blood benzoylecgonine result above 50 µg/L a day or two after they last used the drug.

Where the science becomes contested

Because benzoylecgonine is a marker of past use rather than current impairment, several questions can arise that a forensic toxicologist is well placed to address:

• Is the reported blood concentration consistent with the account of when and how much was used?
• Could the result reflect use days earlier rather than shortly before driving?
• Was the blood sample taken, stored and analysed in a way that could affect the result?
• Is there any suggestion of passive or unknowing exposure that should be considered?

How ATXpert can assist

An independent forensic toxicology report can interpret a benzoylecgonine result in the context of the case, explaining what the number does and does not show, whether it fits the driver’s account, and whether the analytical procedure was sound. Where the science supports it, that interpretation can be set out clearly for the court.

If you are advising a client charged with drug driving on the basis of a cocaine or benzoylecgonine reading, an early expert view can identify the strongest technical points in the case.