What you need to know about drinking and driving

Although a legal limit does exist, it’s always best not to drive after you’ve been drinking. Here are the important reasons why.

Illustration of a person driving a car

Even a small amount of alcohol can affect your judgement and reaction time. This makes driving a motor vehicle after you’ve been drinking a potential danger to your own life and the lives of your passengers, fellow drivers and pedestrians.

To reduce this risk, governments around the world have put in place legal limits for how much you can drink and still drive a vehicle (1). Not complying with these limits can result in fines, losing your licence or even jail time.

Drinking changes how well and how quickly you react and make decisions

As the alcohol you drink is absorbed by the body, some will cross into your brain and affect how it processes information and how you respond to the world around you (2). The more you drink, the higher your blood alcohol content, or BAC (3), and the more alcohol reaches your brain. This, in turn, slows down your reaction time and coordination, and impairs your judgment. BAC is expressed as milligrams of alcohol per litre of blood and is a reliable indicator of how impaired you are that’s used for legal and enforcement purposes.

Countries have set legal BAC limits for drinking and driving, but these limits vary

Virtually all countries in the world have set legal limits on the maximum blood alcohol content allowed when driving a car (1). However, these limits vary. In some countries, no blood alcohol is permitted if you’re driving; in others, a BAC of up to 0.08 is allowed. A zero-tolerance policy is often in place for novice drivers and those learning to drive.

BAC limits are enforced by police, either through roadside breath testing or from blood samples. If you exceed the limit, you’re breaking the law. In certain jurisdictions, people who have repeatedly been caught with excessive BAC may have to use an alcohol interlock device before driving, which requires them to blow into a mouthpiece to start their vehicle and can prevent the engine from running if they’ve been drinking.

There’s a direct relationship between the amount of alcohol you drink and your BAC (3), but how quickly your BAC rises depends on who you are and, of course, how much and how quickly you’ve been drinking. The only reliable way to test your BAC is through a breath or blood test. Whatever the legal limit, the best option is not to drive after you’ve been drinking, and not to drink if you’re planning to drive.

Are you concerned about the effects of drinking on your body?

How much do you really know about alcohol?