The answer to this question depends on the driver’s BAC level. In Ontario, it is illegal to drive a car while your BAC is at 0.08 or higher. Drivers could also face charges if their BAC is somewhere between 0.05 and 0.079.
It is possible for someone’s BAC to be at an illegal level after a night of drinking, depending on what they drank, how much, and genetic and lifestyle factors. That means some people who drive while hungover may be breaking the law.
However, even if you are not technically breaking the law, it may be unsafe to be behind the wheel while experiencing symptoms of a hangover.