Drug driving and UK law

You should know that drug-driving is illegal in the UK, but did you know that prescription medication could impact your ability to drive safely too? 

Research from the charity Brake reveals that drug-driving is a factor in one in 20 fatal crashes. This is a worrying figure. So why are people taking the risk? 

We take a look at the consequences of driving under the influence of drugs, driving under medication, and drug-driving limits as well as drug-driving penalties.

Driver tipping medication into their hand while sitting in the car


What are the effects of drug-driving?

Drugs affect drivers in several different ways.

Some of the more minor effects include:

  • Slower reactions
  • Poor concentration
  • Overconfidence
  • Reduced inhibition 
  • Poor coordination

And of course, the effects could be serious and last for hours, even days.


What are the drug-driving limits for prescription and illegal drugs?

In 2012, the government set new limits on illegal and medicinal drugs in the body. 

The government identified 8 drugs as being most associated with illegal use. They also identified 8 medicinal drugs that had the potential to impact on driver ability. These include sleeping pills like Temazepam and painkillers such as Morphine and Lorazepam, that's often used to treat anxiety.

The government set drug-driving limits for both groups. The threshold for the 8 illegal drugs was set purposely low to enforce a zero-tolerance approach.

In 2015 the list was updated to include amphetamines too.

'Illegal' drugs Threshold limit in microgrammes per litre of blood (UG/L)
Benzoylecgonine (a substance associated with cocaine use)
Lysergic acid diethylamide (LSD)
Methylamphetamine (meth)
Methylenedioxymethamphetamine (MDMA)
6-monoacetylmorphine (heroin)
'Medicinal drugs' Threshold limit in microgrammes per litre of blood (UG/L)
50 µg/L

The threshold limit for amphetamine is higher at 250ug/L to reflect its medicinal use.


How do different drugs affect my driving?

There are 3 main types of drugs that can have significant effects on your driving:

  • Hallucinogens
  • Stimulants
  • Depressants

Most recreational drugs fall under at least 1 of these categories. Here's how the most common drugs could affect your driving:


Cannabis is a depressant and works like a sedative. It slows your reaction times as well as your perception of time and distance - a bad combination for someone who's driving. Brake claims that experiments with driving simulators show that a driver who's taken cannabis is less able to steer the car properly and is slower to react to a car pulling out.


Opiates such as heroin, methadone and codeine can cause drowsiness, mental confusion and visual impairment even with a low dose. Your reaction times are also reduced. As you might expect given the symptoms, opiates are depressants.


Cocaine is a stimulant and often makes the user feel over-confident. As a result your driving is likely to be erratic. You might take greater risks, including high-risk manoeuvres and driving at high speeds. At the end of a night on cocaine a driver might also feel sleepy and suffer from poor concentration.


Ecstasy (MDMA) makes your heart beat faster and can often result in a surge of adrenaline. This can make you over-confident and impulsive often leading to higher levels of risk taking. A driver on ecstasy might suffer anxiety, panic attacks, paranoia and psychosis that can all impede driving ability.


LSD is a hallucinogen, similar to other recreational drugs like magic mushrooms. Users often feel that time is speeding up or slowing down, making it hard to judge their own driving speeds as well as those of other vehicles on the road. Colours, sounds and vision might be distorted too, adding to an overwhelming sense of confusion and disorientation.


Can the police stop and drug test you for no reason?

The police can stop any driver that they judge to be under the influence of drugs. 

If stopped for drug-driving in the UK, you’re likely to be asked to complete a ‘field impairment assessment’. This usually involves being asked to walk in a straight line or counting while standing on one leg. They might check your pupils too.

Roadside drug testing kits might also be used, that can detect both cannabis and cocaine. These test a sample of your saliva and give results in a couple of minutes. Other drugs require a visit to the police station for a blood test.


What happens if I’m caught drug-driving?

If the police believe you’ve taken drugs and are unfit to drive - either as a result of a roadside drug test or field impairment assessment, they’re likely to arrest you. You're likely to be taken to a police station for further blood and urine tests.

To convict you under Section 4 of The Road Traffic Act 1988 (for driving while unfit through drugs), the police need to prove that your driving was impaired. If they can prove that you’ve exceeded the legal level for a certain drug (under section 5a), then it doesn’t matter whether your actual driving was impacted or not, as it's considered to be impaired anyway.


UK drug-driving penalties

If you’re convicted of drug-driving in the UK then you could ge:

  • A driving ban for up to 1 year
  • An unlimited fine
  • Up to 6 months in prison
  • A criminal record
This is even for a drug-driving first offence in the UK.

Convictions appear on your licence, that might affect your job if you drive for a living. You could also face much higher car insurance costs the next time you come to renew your policy. Some insurers may refuse to offer cover at all.

Having a driving and/or drug conviction might also restrict your overseas travel. Some countries don’t allow access to people with drug offences on their record.

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Prescription drugs and driving law

Drug-driving in the UK is illegal if it impairs your ability to drive, whether the drug is legal or illegal. 

If you’ve been prescribed any of the drugs in the medicinal section of the table, speak to your doctor. You can usually drive after taking these medicines if you’ve been given advice by a healthcare professional. For more information visit GOV.UK.

Some hay fever medications, such as chlorphenamine, hydroxyzine and promethazine, are known to cause drowsiness as a side effect.

Therefore, you shouldn’t take this sort of medication, or any other that says ‘may cause drowsiness’, if you’re planning on driving. 

Solicitor Advocate David Barton says to be mindful that any prescription medication should be taken as instructed, especially if you plan on driving: 

"Driving with illegal drugs or when your driving is impaired by drugs of any kind is viewed seriously by police and courts. Drug-driving convictions bring an almost automatic disqualification for a minimum of 12 months.

"The same applies if you fail to take medication that you should - for example, insulin if you're diabetic." 

When it comes to medication, always follow the advice of your doctor or healthcare professional. Or see the patient information leaflet that comes with the medicine.

If you feel any symptoms occurring, or your driving is impaired in any way - even when taking the correct amount, you shouldn't drive.