Drug Driving Law UK: Penalties, Prescription Medicines and the NI Proposals

#What counts as drug driving in Great Britain?

The law in England, Wales and Scotland creates two separate offences. The first is driving, or attempting to drive, while unfit through drugs. This applies to any drug, whether prescribed, over the counter or illegal, if it impairs your ability to drive safely. It is the same test as for alcohol impairment and uses the same standard: would a police officer, applying the roadside field impairment tests, conclude you were unfit to drive?

The second offence was introduced in 2015 and applies to illegal drugs only. It sets blood concentration limits for 16 controlled drugs, including cannabis, cocaine, heroin, ecstasy and ketamine. You are guilty of this offence if the level of a specified drug in your blood is above the limit, even if your driving is entirely normal and even if you feel perfectly fine. The limits for illegal drugs are set at very low levels, in some cases barely above what a confirmatory lab test can detect. The law does not require the police to show your driving was affected.

#How police test for drug driving at the roadside

If police believe you may be unfit to drive, they can carry out a field impairment assessment at the roadside. This is a series of physical checks, such as asking you to walk in a straight line, tracking a moving object with your eyes, or touching your nose with your eyes closed. These tests are not pass or fail in a binary sense; a trained officer uses the results alongside their own observations to form a view about whether you are impaired.

Police can also use a roadside drug testing kit. As of 2026, these kits screen for cannabis and cocaine specifically. If the screening test comes back positive, or if the officer believes you are unfit regardless of the screening result, you will be arrested and taken to a police station where a blood or urine sample is taken. That sample is then analysed by a laboratory to confirm the substance and concentration.

#GB law versus Northern Ireland: how they differ

The difference matters if you drive in both Great Britain and Northern Ireland. A driver in Northern Ireland who has cannabis in their system at a level that would be an offence under GB law is not automatically committing an offence in NI under current law, provided they are not impaired. However, since PSNI started roadside drug screening in 2024, officers can still arrest and test anyone they believe is unfit to drive. The DfI consultation launched on 4 November 2026 would, if passed, bring NI broadly in line with GB practice.

#Prescription medicines: when you can still drive legally

The blood-level limit offence in Great Britain includes specified limits for eight prescription drugs as well as illegal drugs. However, the law includes a medical defence: if the drug was prescribed to you, you took it in accordance with a healthcare professional's advice, and it did not make you unfit to drive, you have a defence even if your blood level is above the specified limit. This defence only applies to prescribed medicines, not illegal drugs.

If you are prescribed any of these medicines and you drive, keep the prescription with you so you can produce it at a roadside stop. The burden of proof for the medical defence sits with you: you need to show the medication was legally prescribed and you followed healthcare advice. If a drug in this list makes you drowsy or impairs your reactions, you must not drive, regardless of whether you have a valid prescription.

#What a conviction means for new drivers

For anyone who passed their driving test within the last two years, a drug driving conviction is especially serious. Under the New Drivers Act 1995, a new driver's licence is automatically revoked if they accumulate six or more penalty points within two years of passing. Drug driving carries a mandatory minimum 1-year ban, so the licence is gone before the question of revocation arises. When the ban ends and the driver reapplies, they restart the two-year probationary period from scratch and must pass both the theory and practical tests again.

The 11-year licence endorsement also sits with the driver for the whole of their early driving career. Any employer who runs a standard DBS check or requests a DVLA licence summary will see the conviction. This affects jobs requiring driving as well as many professional licences, including HGV and PCV categories. A criminal record for drug driving can also complicate applications for jobs that involve working with vulnerable adults or children, regardless of whether a vehicle is involved.

#The Northern Ireland consultation: what is proposed and what is not yet law

On 4 November 2026 the Northern Ireland Infrastructure Minister launched a 12-week public consultation on modernising NI's drug driving law. The consultation, which closes on 27 January 2027, proposes a two-tier system: keeping the existing impairment offences and adding new offences linked to specified drug limits. The proposals include powers to list drugs and set their limits in future regulations, a statutory medical defence for medicines legitimately prescribed for medical or dental purposes, and penalties broadly aligned with the existing GB approach.

The DfI also noted that since PSNI began roadside drug testing in 2024, just over half of all drivers screened tested positive for cannabis and/or cocaine. That rate informed the decision to consult on adding limit-based offences. The consultation invites views on whether the proposals are proportionate, what drugs should be listed, and whether rehabilitation courses would be appropriate for first-time offenders.

#Sources and further reading