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What are the effects of drugs on my driving?

Illegal drugs can compromise your driving ability. But did you know prescription medicine can affect your driving too? Here’s what you need to know. 

Most people know that drugs can affect your ability to drive. But according to our research, almost a quarter (23%) of drivers admit to driving while under the influence of prescription drugs.*

And one in 10 (11%) have admitted to being under the influence of illegal substances while behind the wheel. 

A driver with pills on outstretched hands

These are worrying stats. 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.

 

The effects of drugs on driving

Drugs can affect drivers in a number of different ways.

Some of the more minor effects include slower reactions, poor concentration, overconfidence and poor co-ordination, to name a few. 

And of course, the effects can be far more serious and last for hours, even days.

 

Drug driving limits: prescription and illegal

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

The government identified eight drugs as being most associated with illegal use. They also identified eight medicinal drugs that had the potential to impact on driver ability.

Limits were set for both of these. The threshold for the eight 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)
50µg/L
cocaine
10µg/L
cannabis
2µg/L
ketamine
20µg/L
lysergic acid diethylamide
1µg/L
methylamphetamine (meth)
10µg/L
methylenedioxymethamphetamine (MDMA)
10µg/L
6-monoacetylmorphine (heroin)
5µg/L

 

'MEDICINAL' DRUGS THRESHOLD LIMIT IN MICROGRAMMES PER LITRE OF BLOOD (UG/L)
clonazepam
50 µg/L
diazepam
550µg/L
flunitrazepam
300µg/L
lorazepam
100µg/L
methadone
500µg/L
Morphine
80µg/L
oxazepam
300µg/L
temazepam
1000µg/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 three main types of drugs that can have significant effects on your driving: hallucinogens, stimulants and depressants.

Cannabis is a depressant. It slows reaction and decision times as well as the user’s perception of time and distance, potentially leading to lack of control.

Opiates such as heroin, methadone and codeine can cause drowsiness, mental confusion and visual impairment even with a low dose. Your reaction times will also be reduced.

Cocaine is a stimulant and often makes the user feel over-confident. As a result you might take greater risks, including high-risk manoeuvres, and driving at speed.

Ectasy (MDMA) can cause altered sensory perception, affecting your vision and hearing. It also acts in a similar way to cocaine as it can cause over-confidence and unnecessary risk taking.

LSD is a hallucinogen. There's not a great deal known about the effects of it, but it's thought that it causes chemicals to over-produce in the brain, causing confusion and over stimulation. Hallucinations, reduced reaction time and blurred vision are also linked with LSD.

 

What happens if I’m caught drug driving?

If the police suspect you’re under the influence of drugs, you’ll be stopped and may be asked to do what’s known as ‘a field impairment assessment’. 

As part of this test you could be required to perform a number of balance and coordination exercises, such as walking in a straight line or counting while standing on one leg. 

What’s more, your pupils may be checked for their size and reaction to light as some drugs can cause pupils to shrink or enlarge.

In addition to this, a roadside drug kit may be administered. This is a handheld test system that can detect the presence of certain drugs in your system, including cannabis and cocaine, from a single oral fluid sample. It works in a matter of minutes.

If drugs are found in your system you’ll be arrested, then a blood or urine test will be administered. If the test is positive you’ll be charged. 

 

What happens after I’m convicted?

If you’re convicted then you could receive a driving ban for up to one year, an unlimited fine, up to six months in prison and a criminal record. 

Your conviction will also appear on your licence, which may affect your job if you drive for a living. 

You could also face much higher car insurance premiums.

Having a driving and/or drug conviction may restrict your overseas travel. Some countries don’t allow access to drivers with this kind of offence on their record.

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What's the law on driving and prescription medication?

Driving under the influence of any drug 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 if you’ve been given advice by a healthcare professional.

For more information visit GOV.UK.

Some hayfever 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. 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. 

 

*Figures taken from omnibus research carried out by OnePoll on behalf of Confused.com. This was a nationally-representative poll of 2,000 UK motorists taken between 19 and 23 June 2020.