Drink and drug driving

In England, Wales and Northern Ireland the drink drive limit is:

• 80 milligrams of alcohol per 100 millilitres of blood.
• 35 micrograms per 100 millilitres of breath.
• 107 milligrams per 100 millilitres of urine.

In Scotland, the legal amount you can drink before driving is:

• 50 milligrams of alcohol in every 100 millilitres of blood.
• The breath alcohol equivalent is 22 micrograms of alcohol per 100 millilitres of breath.

 People often think in terms of Units of Alcohol, so here is some guidance on these.

What is an alcohol unit?

Drink unit calculator

It’s illegal to drive with drugs if either:

• You’re unfit to do so because you’re on legal or illegal drugs.
• You have certain levels of illegal drugs in your blood (even if they have not affected your driving).

Legal drugs are prescription or over-the-counter medicines. If you’re taking them and not sure if you should drive, talk to your doctor, pharmacist or healthcare professional.

It’s illegal in England, Scotland and Wales to drive with legal drugs in your body if it impairs your driving.

It’s an offence to drive if you have over the specified limits of certain drugs in your blood and you have not been prescribed them.

Talk to your doctor about whether you should drive if you’ve been prescribed any of the following drugs:

• Amphetamine, for example Dexamphetamine or Selegiline
• Clonazepam
• Diazepam
• Flunitrazepam
• Lorazepam
• Methadone
• Morphine or opiate and opioid-based drugs, for example Codeine, Tramadol or Fentanyl
• Oxazepam
• Temazepam

 You can drive after taking these drugs if:

• You’ve been prescribed them and followed advice on how to take them by a healthcare professional.
• They are not causing you to be unfit to drive, even if you’re above the specified limits.

You could be prosecuted if you drive with certain levels of these drugs in your body and you have not been prescribed them.

The law does not cover Northern Ireland - but you could still be arrested if you’re unfit to drive

Although many people think they are driving safely, alcohol impairs their judgement, reaction times and sense of reality.

It affects driving ability by causing: 

• Delayed reaction times.
• Blurred vision.
• Drowsiness.
• Inability to think, reason or plan ahead.
• Reduced concentration .
• Reduced ability to interpret road signs and speed limits.
• An inability to judge your position on the road, making it easy to cross the centre line etc.
• Impaired assessment of risk.

The only safe limit is no alcohol.

How the body processes alcohol differs from person to person, and this depends on a number of factors:

• Amount and type – how much alcohol has been taken how quickly.
• Age – younger people have lower alcohol tolerance, coupled with a lack of driving experience.
• Weight/size – the smaller you are, the lower your blood volume is likely to be and alcohol may affect you more.
• Gender – women are typically smaller and have proportionately more body fat and less body water than men, so drinking the same amount of alcohol is likely to result in a higher blood alcohol concentration.
• Water intake – dehydration leads to a higher concentration of alcohol in the blood.
• Food intake – alcohol is absorbed more slowly if there is food in the body.

If you take drugs as well as alcohol, your ability to drive safely will be affected even more, increasing further your risk of being involved in a collision. 

Different drugs affect driving differently, and people can also react to drugs differently.

The type of drug, the dosage, the length of time in the user's body, as well as the user themselves, all impact on how much a driver is affected.

A drivers’ attentiveness, perception of time and speed, as well as coordination and judgement can all be affected when using drugs.

Drug drivers can experience a range of effects, including:

• An inability to notice hazards.
• Lower reaction times.
• Erratic, aggressive and risk-taking behaviours.
• An inability to concentrate properly on driving tasks.

 Drugs may also cause:

• Nausea.
• Hallucinations.
• Confusion.
• Panic attacks.
• Paranoia.
• Tremors.
• Dizziness.
• Fatigue.

If alcohol has also been consumed, this will further increase the risk of being in a collision. 

Drugs that can be tested for at the roadside are cannabis and cocaine, while the evidential laboratory test can identify all the drugs covered by the law, including ecstasy, LSD, ketamine and heroin.

Police now make use of drug wipe and saliva testing kits to catch those who are unfit to drive having taken drugs. This has led to an increase in convictions.

If you are pulled over by the police on suspicion of drink driving, police officers will first use a breathalyser to establish whether or not you are over the limit. This is called a preliminary test.

There are also two other tests:

• A preliminary field impairment test, which checks whether someone is unfit to drive because he or she is under the influence of either drink or drugs.
• A preliminary drug test. This tests whether a person is unfit to drive because they are under the influence of drugs.

The field impairment test could include the police asking you to perform a balancing exercise, doing a non-invasive eye test, and/or co-ordination exercises.

A preliminary test can be requested either when the police officer reasonably suspects a defendant is driving, has driven or will drive, or be in charge of a vehicle, and reasonably believes a defendant was driving, attempting to drive or be in charge of a vehicle at the time of an accident.

Legal Guidance on Road Traffic - Drink and Drug Driving (for England & Wales)