Drug driving legislation


Drug driving legislation


Many drugs can have a significant adverse effect on a person's ability to drive. It is estimated that there are approximately 200 deaths on roads in the UK each year1 where drugs are implicated as a causative factor. In an attempt to reduce the number of deaths, new drug-driving legislation came into effect on 2nd March 2015. This legislation sets maximum blood limits for sixteen specified drugs, both illicit and prescribed, and makes it an offence to drive with blood levels above those limits.

A survey conducted by Brake and Direct Line2 showed that 7% of UK drivers, admitted to driving after having taken illegal drugs. One in five drivers thinks that they have been a passenger with a driver who had taken drugs. The same survey revealed a worrying complacency over the effects of prescribed or OTC medication on an individual's driving ability with one in six (17%) either ignoring labelled warnings or not checking them. This figure has risen from one in eight drivers surveyed (12%) in 2010.²


By the end of this article you will be able to:

  • describe the impact drugs can have on an individual's ability to drive.
  • outline current drug-driving legislation.
  • counsel patients on the changes to drug-driving legislation and how it might affect them.
  • explain the concept of a statutory medical defence.
  • understand current driving legislation in relation to certain medical conditions.

Effects of drugs on driving

Illegal drug use can cause highly unpredictable effects on a person and these can be lethal when combined with driving. The effects of drugs, particularly sedating effects, can lead to slower reaction times and reduced concentration. Other effects can result in over-confidence that can lead to increased risk taking and erratic behaviour. In addition, combining illegal drugs with alcohol significantly increases the risks. An analysis in the USA found that drivers who had taken illegal drugs and consumed alcohol were twenty three times more likely to be involved in a fatal crash than were sober drivers.3

In the same way, prescription and over-the-counter medicines can affect an individual's ability to drive by causing drowsiness or affecting co-ordination, concentration, vision and reaction times. Medicines that can affect a person's ability to drive must legally carry a warning label, but the Brake and Direct line survey revealed that 17% of UK drivers admit to either ignoring warning labels or not checking the label before driving.²

It is the clinical responsibility of prescribers and suppliers of medicines (i.e. pharmacists) to advise patients on the likely risks associated with their medicines. This will include, for some drugs, the advice that the ability to drive may be impaired.

Historic Drug driving legislation

Previosuly under section 4 of the Road Traffic Act 1988, the police could prosecute drivers whose driving was proved to be impaired due to drugs, irrespective of whether these drugs had been prescribed or not.

If the police stopped someone and thoguht they were under the influence of drugs they could do a "Field Impairment Test" (FIT). This is a series of tests designed to assess the level of impairment experienced by the driver. The FIT includes checking the size of the driver's pupils and how they react to light, tests for balance, co-ordination and judgement such as standing on one leg whilst counting out loud. Drivers who failed the FIT could then be arrested and taken to a police station for a blood test that would confirm whether they have taken drugs or medicines that could affect their ability to drive.

If convicted of 'drug driving' the penalties included a minimum of a one year driving ban, a fine of up to £5000 and a criminal record. This conviction was recorded on the individual's driving licence for eleven years, resulting in increased car insurance and possible difficulty travelling to certain countries such as the USA.

Current drug driving legislation - April 2015

Legislation was passed in April 2015, Section 5A of the Road Traffic Act 1988, which set maximum blood levels for a number of controlled drugs. The legislation creates a new offence of "driving, attempting to drive or being in charge of a vehicle with a specified controlled drug in the body, in excess of a specified limit". The law came into effect on 2nd March 2015 and pharmacists are required to advise patients accordingly.

The Department for Transport has prepared guidance to support healthcare professionals advising patients on the new legislation. We would encourage you to access and read this document which has formed the basis of this module: Department for Transport; Guidance for healthcare professionals on drug driving; July 2014.

The drugs affected by this revised legislation are broadly divided into two groups. The first group includes drugs that are more commonly abused and consequently have very low limits set. The second group includes drugs that have a recognised therapeutic use and consequently the specified limits are higher.

The "zero tolerance" group comprises the following drugs with the specified limits:

Drug Specified limit (mcg/l)
Cannabis (THC)* 2
Cocaine 10
MDMA (Ecstasy) 10
Lysergic Acid Diethylamine (LSD) 1
 Ketamine 20
 Heroin/diamorphine metabolite (6-MAM) 5
 Methylamphetamine 10
*Tetrahydrocannabinol (THC) is the active ingredient of cannabis.

As the limits for these drugs are set low any user will be likely to test above the specified limit, leading to a probable conviction. However, patients who have been prescribed one of the listed medicines by a doctor or dentist would be entitled to a statutory "medical defence" – to be discussed later in this module.

The second group of drugs comprises those that have a recognised therapeutic use. The specified limits have been set significantly higher than would be expected through normal therapeutic use.

Patients taking their medication as prescribed are therefore unlikely to exceed the limits unless their dose is outside the usual range.

Drugs included in this second group with their specified limits are:

 Drug  Specified Limit (mcg/l)
 Clonazepam 50
 Diazepam 550
 Flunitrazepam (no longer licensed in the UK) 300
 Lorazepam 100
 Oxazepam 300
 Temazepam 1000
 Methadone 500
 Morphine 80
 Amphetamine** 250
** Seperate legislation was introduced for amphetamine on 14th April 2015. The specified limit takes into account the legitimate medicinal use of amphetamine alongside its potential for abuse. This raises potential issues for patients prescribed drugs like selegiline which can be metabolised into amphetamines (selegiline is metabolised into l-methamphetamine and l-amphetamine).

The Department of Transport estimates that approximately 19 million prescriptions are issued each year for the medicines included within this revised legislation.4

Police have the power to screen for these drugs at the road-side by using devices that detect the specified drug in saliva. This ascertains whether the driver has taken one of the specified drugs, or a pro-drug thereof. A positive screening test will require the driver to provide a blood sample to determine the level of drug in the blood. This may then be used as evidence to enable prosecution if the level exceeds the specified legal limit.

Statutory medical defence

Where a driver has been shown to have exceeded a specified limit, and therefore committed an offence, a statutory medical defence exists to protect those who have been legitimately prescribed the drug. This form of defence can be raised at any point providing that the drug was:

  • Lawfully prescribed, supplied or purchased over the counter and used for medical or dental purposes;
  • Taken in accordance with the advice given by the prescriber or supplier and in accordance with any written instructions, such as the patient information leaflet (PIL).

This medical defence remains valid where a prescribed medicine is used outside of the manufacturer's licence and the prescriber's advice differs from the general information given in the PIL.

It is very important to note that, even where the medical defence applies, if a person's driving is shown to be impaired they are still liable for prosecution under section 4 of the act. Even where a drug has been lawfully prescribed it will always be the patient's responsibility not to drive if they believe their driving may be affected.

Advice to patients

Patients who are lawfully using medicines covered by the legislation can be reassured that they will be able to drive without risk of prosecution, provided their ability to drive is not impaired. To be clear, the driver can avoid prosecution for exceeding the specified blood limit provided that the drug has been taken as prescribed and it has not impaired their driving.

In order to speed up any investigative process patients should be advised to carry evidence to show that they are taking their medication as prescribed. Suitable evidence would include a repeat prescription request slip or the PIL from an OTC medicine.

Patients should be reminded that combining alcohol with any of the specified drugs will significantly increase the risk of accidents and any impairment of their driving would render them unable to claim a statutory medical defence.

Patients should be made aware that drug interactions with other prescription and OTC medicines could increase the blood levels of their controlled drug. This could lead to exceeding the specified limit as well as impairment of driving where previously there had been no effect. Pharmacists and prescribers should consider the significance of any drug interaction for a patient taking one of the medicines covered by the legislation.

It is always the driver's responsibility to decide whether their driving is or may be impaired. However, patients should always be made aware of the risks when supplied with any drug with the potential to affect their ability to drive.

Appropriate advice to provide to patients regarding medicines and driving includes:

  • Do not drive if you experience any symptoms that suggest driving may be impaired such as sleepiness, poor co-ordination, slowed thinking, visual problems, dizziness or drowsiness.
  • Be extra vigilant when first starting a new medicine or when increasing or reducing the dose.
  • Be aware that alcohol will increase the risk of accidents when taken in combination with other drugs that can impair the ability to drive.
  • Certain circumstances will increase the risk of driving being impaired. These could include:
    • Addition of another prescribed medicine that also impairs driving.
    • Combining prescribed medication with OTC medicines that can impair driving ability.
    • Any developing medical conditions that could increase the risk of side effects associated with impaired driving ability, this could include medical conditions associated with significant weight loss.
    • Starting a new medicine that can affect the metabolism of the existing medicine.
    • Increasing age can reduce a person's tolerance to the effects of a drug - this can increase the risk of driving being impaired.

Medical conditions that may impair driving (covered by existing legislation)

Pharmacists should be able to explain to patients how their medical conditions and/or treatments may affect their ability to drive. This includes explaining the legal implications of driving whilst impaired or with excessive levels of drug in their system.

Patients are also likely to enquire about how a medical diagnosis might affect their ability to drive and whether they need to inform DVLA. While it would be impossible to be prepared to advise on every medical condition it is valuable to understand the implications of some common medical conditions and also where to source information on behalf of patients.

The regulations governing driving with a specified medical condition are complicated and cover a variety of scenarios. Full details are outside the scope of this article. DVLA has issued a guide for medical practitioners that looks at a number of medical issues in detail. Pharmacists are advised to refer to this guide in order to ensure they are giving accurate advice.

The information below relates only to Group 1 licences – car/motorcycle.

Diabetes - drivers who are being treated with insulin for their diabetes must inform the DVLA. Blood glucose levels should be maintained above 5mmol/l whilst driving. If the patient's blood glucose is below 5mmol/l they should have a snack and if it is lower than 4mmol/l or there are any signs of hypoglycaemia they must not drive. Diabetic patients should be advised to keep an emergency supply of fast-acting carbohydrate within easy reach in their car. Patients should be advised to check their blood glucose levels no more than two hours before they drive and every two hours whilst driving.

Epilepsy - this is the most frequent cause of drivers losing consciousness at the wheel. To qualify for a driving licence an epileptic patient must be seizure free for one year. Patients who suffer seizures as a result of a change or reduction of anti-epileptic medication will have their driving licence revoked for twelve months.

Cardiovascular conditions:

  • Angina - patients experiencing symptoms at rest, with emotion or at the wheel should be advised to stop driving. They can start to drive again once satisfactory symptom control is achieved. DVLA do not need to be notified.
  • Arrhythmia - patients should be advised to stop driving where arrhythmias cause or are likely to cause incapacity. Driving may be permitted where the underlying cause of the arrhythmia has been identified and controlled for at least four weeks. DVLA do not need to be notified unless symptoms are either distracting or disabling.
  • Hypertension - patients should be advised that they can continue driving providing treatment does not cause unacceptable side effects. DVLA do not need to be informed.
  • Stroke/TIA - patients suffering a single stroke or transient ischaemic attack should not drive for a period of one month from the attack. There is no requirement to inform DVLA unless the patient has suffered some residual neurological deficit one month after the episode.

Parkinson’s disease - where the condition is disabling and/or there is significant variability in motor function the patient's licence is likely to be revoked but where their driving would not be impaired then the patient may retain their driving licence, subject to regular medical review.


A person's ability to drive can be impaired by their medical condition or by a medicine they may be taking. The role of the pharmacy team is to advise patients when there is a risk their driving may be affected. The legislation makes it an offence to be in charge of a vehicle when exceeding specified blood levels of certain controlled drugs. Provided the controlled drug has been prescribed and taken as directed, a statutory medical defence exists. This defence does not apply if the person's driving has been impaired by use of the drug.


  1. Department for Transport. Regulations to specify the drugs and corresponding limits for the new offence of driving with a specified controlled drug in the body above the specified limit- A Consultation document (accessed online Jan 2015) 
  2. Direct Line and Brake Fit to Drive with medication and driving 2015-2017 (accessed online July 2018) 
  3. Li G, Brady JE, Chen Q. Drug use and fatal motor vehicle crashes: A case-control study. Accident Analysis & Prevention. 2013; 60: 205-210.
  4. Department for Transport. Drug Drive Partner Pack. Am I fit to drive? 
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