UK Drug Driving Laws: Limits, Penalties, and Medical Defence

UK drug driving laws make it a criminal offence under Section 5A of the Road Traffic Act 1988 to drive, attempt to drive, or be in charge of a motor vehicle with any of 17 specified controlled drugs in your blood above a set limit. The rules came into force in England and Wales on 2 March 2015, and Scotland adopted the same framework with identical limits in October 2019.¹ A conviction carries a minimum 12-month driving ban, an unlimited fine, and up to six months in prison. The prosecution does not have to show the drug affected your driving. A blood result above the limit is enough.

How the Offence Works

Section 5A is a strict liability offence based on blood concentration. If your blood exceeds the specified limit for one of the listed drugs, the offence is made out, regardless of whether you drove badly or posed any danger. That is the key change from the older impairment-based offence under Section 4, which required the prosecution to prove you were actually unfit.

There are two forms of the offence. The first is driving or attempting to drive. The second is being “in charge” of a vehicle while over the limit, which can apply even if you were not moving and the engine was off.¹ The in-charge version carries lighter penalties (up to three months in prison and either a disqualification or 10 penalty points) but still produces a criminal record. A defence to the in-charge offence exists if you can prove there was no likelihood of you driving while still above the limit.

Limits for Illegal Drugs

For drugs used recreationally, the thresholds are set at or near the lowest level forensic labs can reliably detect. The policy intent is effectively zero tolerance. All limits are in micrograms per litre of blood:²

Cannabis (Delta-9-THC): 2 µg/L
Cocaine: 10 µg/L
Benzoylecgonine (cocaine metabolite): 50 µg/L
MDMA (ecstasy): 10 µg/L
Ketamine: 20 µg/L
Methamphetamine: 10 µg/L
6-Monoacetylmorphine (heroin metabolite): 5 µg/L
LSD: 1 µg/L

The cannabis limit of 2 µg/L is designed to catch recent use rather than exposure days earlier, but heavy regular users can remain above it longer than they expect, and there is no reliable way to calculate when you will drop below. Cocaine has a limit of 10 µg/L, while its metabolite benzoylecgonine is set higher at 50 µg/L because it lingers in the blood after the drug’s effects have worn off. The practical effect is that both recent and fairly recent use can trigger the offence.

Limits for Prescribed Medicines

Several controlled drugs commonly prescribed by doctors are also on the list, but at much higher thresholds. The limits are intended to accommodate normal medical use:²

Amphetamine: 250 µg/L
Clonazepam: 50 µg/L
Diazepam: 550 µg/L
Flunitrazepam: 300 µg/L
Lorazepam: 100 µg/L
Methadone: 500 µg/L
Morphine: 80 µg/L
Oxazepam: 300 µg/L
Temazepam: 1,000 µg/L

Exceeding these limits is still a criminal offence even with a valid prescription, unless the statutory medical defence applies.

The Medical Defence

If you are charged, Section 5A gives you a specific defence provided three conditions are all met:¹

The drug was prescribed or supplied to you for medical or dental purposes.
You took it in accordance with the prescriber’s directions and the manufacturer’s instructions in the patient information leaflet, so far as those are consistent.
Your possession of the drug was lawful under the Misuse of Drugs Act 1971.

The defence falls away if you ignored any advice from your prescriber about when it is safe to drive, or ignored the equivalent advice from the manufacturer. Taking a larger dose than prescribed has the same effect. So if your GP told you not to drive for four hours after taking morphine and you drove after two, the defence is gone, even if your blood level was below the limit.

How the burden works matters. Once you produce enough evidence to raise the defence (prescription records, pharmacy labels, evidence of your dosage), the court must assume it is satisfied unless the prosecution can disprove it beyond reasonable doubt.¹ Keeping your prescription paperwork and patient information leaflets accessible is the practical lesson.

Being Tested by Police

A stop usually starts with an officer suspecting drug use (because of driving, smell, appearance, or something else at the scene). You will be asked to give a saliva sample using an approved roadside device. The one currently in use is the Securetec DrugWipe, which screens for cannabis and cocaine.

The roadside test is a screening tool, not evidence. If it indicates cannabis or cocaine, or the officer suspects a drug the device does not cover, you will be arrested and taken to a police station. There, a healthcare professional takes a blood sample. That sample is the actual evidence the prosecution will use.

The blood sample is split into two portions. One goes to the prosecution’s laboratory. The other is offered to you so you can arrange independent analysis. Taking that portion and getting it tested separately is one of the strongest tools you have for challenging the result, and discrepancies between two lab analyses can form the basis of a defence.

Refusing a Test

Refusing to cooperate is itself an offence carrying the same penalties as drug driving. Under Section 6(6), failing without reasonable excuse to provide a roadside saliva sample is an offence. Under Section 7(6), failing without reasonable excuse to provide a blood or urine specimen at the station is an offence.³ The maximum penalties are the same: up to six months in prison, an unlimited fine, and a minimum 12-month ban. Refusing in the hope of avoiding a positive result leaves you with the same punishment and none of the defences, including the medical defence, that you might otherwise have run.

Penalties

A conviction for driving or attempting to drive above a specified limit carries:⁴

A minimum 12-month driving ban. This rises to at least three years if you have been convicted of a relevant drink or drug driving offence in the previous 10 years, and to at least two years if you have had two or more disqualifications of 56 days or longer in the preceding three years.
An unlimited fine, calculated by reference to your income and the seriousness of the offence.
Up to six months in prison, most likely where there are aggravating factors such as an accident, passengers, or very high drug levels.
A criminal record that can affect employment, travel, and professional licences.

The in-charge offence has a lower ceiling of three months in prison and a level 4 fine, with either disqualification or 10 penalty points.⁴

The conviction is recorded on your licence as endorsement code DG10 and stays on your driving record for 11 years from the date of conviction.⁵ The in-charge equivalent, DR90, lasts four years. Insurance premiums rise sharply after a conviction. Industry data from 2024–2025 showed a median premium of around £1,705 for drivers with a drug-driving conviction, against about £413 for drivers with a clean record, and some insurers decline cover entirely. With DG10 lasting 11 years, the cost is long-running.

Unlike drink driving, there is no rehabilitation course for drug driving that can reduce your disqualification. The ban runs for its full length.

Scotland and Northern Ireland

Scotland adopted its own regulations in October 2019 under the Drug Driving (Specified Limits) (Scotland) Regulations 2019.⁶ The 17 substances, the thresholds, the testing process, and the penalties are the same as in England and Wales. Northern Ireland has not adopted equivalent specified-limit regulations under Section 5A, and enforcement there still relies on the impairment-based offence under Section 4, which requires proof that the driver was actually unfit.

If You Are Stopped

Cooperate with the roadside test. Refusing is a separate offence with the same penalties and strips away defences you might otherwise have. If you take prescribed medication, keep your prescription details, pharmacy labels, and the patient information leaflet somewhere you can produce them easily, whether in the car or on your phone. Those documents are the foundation of the medical defence, and producing them early can sometimes resolve matters before charging.

If you are arrested and a blood sample is taken, take the second portion when it is offered and arrange independent analysis. A solicitor or the testing lab can advise on how to store and transport it correctly. The prosecution’s laboratory result is not infallible, and a competing analysis is one of the strongest ways to challenge a charge.

1
Legislation.gov.uk. Road Traffic Act 1988 Section 5A
2
Legislation.gov.uk. The Drug Driving (Specified Limits) (England and Wales) Regulations 2014
3
Legislation.gov.uk. Road Traffic Act 1988 Section 7
4
Sentencing Council. Driving or Attempting to Drive with a Specified Drug Above the Specified Limit
5
GOV.UK. Penalty Points (Endorsements) Endorsement Codes and Penalty Points
6
Legislation.gov.uk. The Drug Driving (Specified Limits) (Scotland) Regulations 2019