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Defences for impaired driving

Information about the defences for the offence of driving while impaired by a drug.

It is a statutory defence to a charge of driving while impaired if:

  • only prescription or non-prescription drugs are present and
  • driver proves that they did not know or could not reasonably be expected to know that the drug taken would impair driving when used according to advice by a registered medical practitioner, dentist or pharmacist and
  • drug was used according to that advice (advice written or oral & includes any labelling or info included in packaging).

Commentary in Motor & traffic law Victoria suggests that it is probable that driver will have legal burden of proving that they were authorised to have a particular prescription only drug in their possession.

This defence is not available where a mixture of permissible and illicit drugs are present.

See s. 49(3B)—Road Safety Act 1986 (Vic) and Motor & Traffic Law [5610.263V]

Expert evidence

A certificate from an approved analyst will be sufficient proof that drug was present in blood or urine sample. The necessary particulars are contained in Regulation 207A.
Approved analysts who can provide certificate for proof that drug was present in blood are listed in Government Gazette.

There has been no similar listing of approved analysts for purposes of urine analysis.

More information


Road Safety Act 1986

  • s. 3(1)—defines prescribed illicit drugs
  • s. 49(3B)—defence if analysis carried out discovers only permissible drug and driver did not know would impair driving and the drug was used according to advice

See Road Safety Act 1986 (Vic).


Motor & traffic law Victoria

Motor & traffic law Victoria has commentary of defences, including:

  • an introduction [5610.263A]
  • defence driver while impaired [5610.263V]

See Motor & traffic law—Victoria.