Alcohol, drugs and driving

Driving after drinking or taking drugs is one of the most serious things a driver can get wrong, because it slows reactions, blurs judgement and weakens control long before a person feels drunk. Irish law sets strict limits, and it sets a much lower one for the drivers who are least experienced. The consequences, both legal and human, are severe, and this is a topic the theory test treats seriously.

The two blood alcohol limits

There are two legal limits, measured in milligrams of alcohol per 100 millilitres of blood. For fully licensed drivers the limit is 50mg. For learner drivers, novice drivers in their first years, and professional drivers such as those driving buses, trucks and taxis, the limit is much lower at 20mg. In practice the 20mg limit is so low that even a single drink can put a learner or novice driver over it. Body size, food and the type of drink all change how alcohol affects you, which is another reason not to try to guess whether you are under the limit. The safest approach for any driver, and the only reliable one for a learner, is not to drink at all before driving.

Testing at the roadside

Gardai operate mandatory alcohol testing checkpoints and can require any driver to provide a breath sample. Refusing to give a sample is itself a serious offence. Drug driving is also tested at the roadside using an oral fluid test that can detect substances such as cannabis and cocaine, and impairment by any drug, legal or illegal, is an offence. If a test suggests you are over a limit or impaired, you can be arrested and taken for further testing.

Penalties

The penalties are heavy and are meant to be. Being caught over the limit can bring disqualification from driving, a substantial fine, and in more serious cases a prison sentence. A driving ban has knock on effects on work, insurance and independence that last far longer than the ban itself. Bans apply from the first offence, and repeat offences are treated far more harshly still.

Why impairment is so dangerous

Alcohol and drugs are dangerous behind the wheel because they attack judgement first. That means an impaired driver often feels confident and capable while their reactions, coordination and concentration are all worse than normal. Even a small amount slows how quickly you respond to a hazard, and it narrows how much of the road you take in. This is why the limits are set low, and why feeling fine is never proof that you are safe to drive.

The morning after and prescription medicines

Alcohol leaves the body slowly, at a rate you cannot speed up with coffee, food or a cold shower. A heavy night can leave you over the limit well into the next morning, so the morning after is a genuine risk that catches people out. Some prescription and over the counter medicines also cause drowsiness or slow reactions, so read the label and ask your pharmacist or doctor whether it is safe to drive. To build the wider habits of responsible driving, our Safe and Responsible Driving practice questions cover impairment, fatigue and attitude behind the wheel.