The "Carter" defence in Canadian DUI law.

Components of the "Carter defence" defence, named after the case of R. v. Carter, are still sometimes used in 2026. Carter defences use expert witness testimony to dispute the accused's intoxication level while driving. While the accused’s BAC reading may be above .08, the defence discredits its relevance to guilt. At issue is:

1. the amount of alcohol that was ingested by the accused and in what timeframe;


2. the accused’s likely intoxication level given their age, gender, weight, height, and other personal factors.

The purpose of the Carter defence is to find “reasonable doubt”. You essentially present to the court that given the amount of alcohol ingested in the period of time prior to the arrest and given the accused’s size, it is doubtfdul that the reading is accurate. Judges may acquit based on the Carter challenge.

Carter defences usually require the testimony of the accused or other witnesses to their drinking and a toxicologist (expert witness). The purpose of the expert witness is to say that "the accused would not have been over 80 mgs at the time of driving”. Highlighting relevant factors relating to the accused's personal circumstances (size, weight, medical history) are usually an important part of this analysis.

What is the current state of the Carter defence in Ontario DUI law?

The Federal government recently amended the Criminal Code to further limit Carter type defences by saying it was illegal to be impaired within two hours of driving. Expections remain for getting drunk after driving. When the accused drank and the time of intoxication is still important.

*Please note: DUI law in Canada is constantly changing. It is important to contact a lawyer immediately to determine what defences are currently available options in your particular case.

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