Driving - PatientsCann UK®

Critical: Do not refuse a roadside drug swab or blood test without a medical reason

Refusing to provide a sample when requested by a police officer is a separate criminal offence — regardless of whether you have a medical cannabis prescription. Even if you would have had a valid statutory medical defence against a drug driving charge, refusing a sample can still result in a charge and may undermine your defence. Only refuse if you have a genuine medical reason, and tell the officer clearly. Always seek legal advice as soon as possible if stopped.

Use the tabs below to navigate between key topics. Read each section carefully — especially "Police Stop" and "Drug Testing".

The Law: What Applies to CBPM Patients

UK drug driving law, the legal limit for THC, and the statutory medical defence that protects legitimate patients.

Section 5A Road Traffic Act 1988

It is an offence to drive with a specified controlled drug in your blood above a specified limit. For cannabis (THC), the limit is 2 micrograms per litre of blood. This is a very low limit — even if you have not consumed cannabis before driving, THC may remain in your system for several days and push you above it.

Read Section 5A RTA 1988 →

THC is in the "Zero Tolerance" Group

Cannabis (THC) is classified as a zero tolerance drug under drug driving law — meaning the limit is set very low, not at a level that indicates impairment. This group also includes cocaine, MDMA, LSD, ketamine, heroin metabolite, and methylamphetamine. The difference for patients is that the statutory medical defence is available for THC if certain conditions are met.

The Statutory Medical Defence

Even if you test above the legal limit, you have a valid statutory defence under s.5A(5) RTA 1988 if all three conditions apply:

All Three Must Apply — Statutory Medical Defence

The medicine was prescribed to you
You took it according to your prescriber's instructions
It was not affecting your ability to drive safely at the time

Burden of Proof on the Police — but a Defence is Not a Guarantee

It is the police's job to prove you were impaired while driving. Being over the limit alone does not automatically lead to a conviction where the medical defence applies. However, you must still cooperate fully — refusing a test weakens your position significantly and creates a separate offence. Always seek legal advice promptly.

Home Office advice to prescribers: When prescribing THC-containing CBPMs, patients must be told the medicine is likely to affect their ability to drive, not to drive until they know how it affects them, and that driving while impaired is an offence even with a prescription.

Should I Drive After Taking My Medication?

Understanding impairment, personal tolerance, and when it is safe to get behind the wheel.

No one should drive while impaired

No one — with or without a prescription — should drive while under the influence of any substance that impairs their ability to drive safely. This is your personal responsibility. A prescription does not grant permission to drive impaired; it provides a potential legal defence if you are tested and not impaired.

THC limits & individual tolerance vary

Being above the 2 microgram legal limit does not automatically mean you are impaired — THC affects individuals differently based on tolerance, metabolism, time since consumption, strain, and dose. However, you must be honest with yourself. If you feel drowsy, unfocused, or your reaction times feel slower, do not drive.

Know your own medication

CBD-dominant products with little or no THC are unlikely to impair driving. THC-dominant or balanced products carry a higher risk. Do not drive until you have established how your specific medication affects you, under your prescriber's guidance. Some patients on stable, long-term regimes may feel confident driving — others on high THC doses should avoid it entirely.

Consider timing of your doses

THC can remain detectable for days, but acute impairment typically peaks shortly after consumption and reduces. Talk to your prescriber about scheduling doses to allow driving when needed. Evening dosing may be preferable for patients who need to drive during the day.

Ask your prescriber

Always discuss driving with your prescribing clinician when starting or changing medication.

Know your side effects

Drowsiness, dizziness, or delayed reactions are a sign you should not drive.

Time your doses

Plan your dosing schedule around when you need to drive, in consultation with your clinic.

When in doubt, don't drive

If you feel any uncertainty about your fitness to drive, wait or arrange alternative transport.

If You Are Stopped by Police While Driving

Step-by-step guidance on how to handle a roadside stop calmly and correctly as a CBPM patient.

Stay calm — comply with the stop

Pull over safely, switch off the engine, and remain polite and cooperative throughout. Do not argue, raise your voice, or become confrontational. Your attitude during a stop can influence how the encounter proceeds.

Inform the officer you are a medical cannabis patient

Clearly and calmly tell the officer that you hold a valid UK medical cannabis prescription and that you have your medication with you. Use clear language: "I hold a valid private medical cannabis prescription in the UK. I am happy to show you my documentation."

Show them your medication in its original packaging with the dispensing label, and ideally a clinical letter or copy of your FP10. This information is relevant to whether the statutory medical defence applies.

Do NOT refuse a roadside drug swab — unless you have a medical reason

This is critical. Refusing to provide a sample is a separate criminal offence under Section 6 of the Road Traffic Act 1988. You can be charged for refusal even if you would have had a full statutory medical defence against a drug driving charge.

If you have a genuine medical reason for being unable to provide a sample (e.g. a clotting disorder, needle phobia formally documented, or inability to blow), tell the officer clearly and calmly, and they should record this. Medical inability to provide is different from refusal.

Refusing without a medical reason is a criminal offence and can result in an automatic charge, a fine, possible disqualification, and removes your ability to rely on a medical defence in court.

Note everything down after the encounter

As soon as it is safe to do so, write down the time, location, officers' badge numbers, what was said, what tests were administered, and any other relevant details. This information can be vital if the matter proceeds to court.

Seek legal advice immediately if arrested or charged

If you are arrested, you have the right to free, independent legal advice from a duty solicitor at the police station — always ask for a solicitor before answering any further questions. Contact our legal support resources once you are free to do so.

PatientsCann UK legal support resources →

Common Roadside Scenarios

An officer may tell you that your prescription "doesn't matter" or cannot be used as a defence. Do not argue. Remain calm. Politely state that you understand you may be over the limit but that you have a valid prescription and intend to raise the statutory medical defence under s.5A(5) RTA 1988 if required. Do not resist any testing procedures. The officer's role is to gather evidence — the defence is assessed later by the courts, not at the roadside. Say: "I understand. I have my prescription documentation and will cooperate fully. I would like to note my intention to raise the statutory medical defence."

This is a difficult situation but the prescription still exists — you simply cannot prove it at the roadside. Still cooperate fully with all testing. Do not refuse any tests. Tell the officer you are a patient and that you can provide documentation. Ask whether you can contact your clinic or access a digital copy of your prescription. Once you are home or in a safe place, contact your clinic immediately for a letter and gather your documentation. If you are charged, your legal representative can submit the prescription and medical records as evidence. Going forward, always carry your documents with your medication.

It is highly recommended to keep a printed clinical letter and a copy of your FP10 in your vehicle at all times alongside your medication.

You do not have an absolute right to speak to a solicitor before providing a roadside breath, oral fluid (swab), or preliminary impairment test. These are preliminary roadside procedures. However, once you are arrested and taken to a police station, you have an absolute right to free, independent legal advice — always exercise it. At the station, say clearly: "I wish to speak to a solicitor before I answer any questions or provide any further samples." A duty solicitor is available 24 hours a day and is entirely free of charge.

Roadside Drug Testing: Swabs & Blood Samples

What happens when police use a roadside drug testing device, what a positive result means for patients, and why cooperation is essential.

The Drugwipe / Oral Fluid Test

Police typically use an oral fluid screening device (such as the Dräger DrugTest 5000 or the Cozart RapiScan) to test for drugs at the roadside. This involves a swab taken from the inside of your mouth. As a CBPM patient prescribed THC-containing medicine, you should expect to test positive for cannabis even if you have not consumed that day — THC is detectable in oral fluid for up to 24 hours after use, and sometimes longer.

A positive roadside result is not a conviction

A positive oral fluid test is a preliminary screening only. It gives police reasonable grounds to arrest and take you to a police station for an evidential blood sample. The roadside result itself cannot be used in court — only the lab-analysed blood result can form the basis of a prosecution. A positive blood result above 2 micrograms/litre still does not automatically lead to conviction where a valid statutory medical defence exists.

Always cooperate — do not refuse

Refusing to provide an oral fluid sample at the roadside, or a blood sample at the station, is a criminal offence under Section 6 of the Road Traffic Act 1988. The maximum penalty for refusing is the same as for drug driving itself — an unlimited fine, mandatory disqualification from driving, and a criminal record.

Critically: refusing a sample does not protect you. If you refuse, you cannot benefit from the statutory medical defence. Courts have consistently held that refusal removes the ability to argue medical necessity.

Do not refuse a swab or blood sample. Always provide the sample. Raise your prescription and the statutory medical defence after the test — not instead of it.

The only exception: genuine medical inability

The law recognises that some people are medically unable to provide a sample — not merely unwilling. Examples include a formally diagnosed severe needle phobia, an inability to provide sufficient oral fluid due to medication side effects, or a serious medical condition. If this applies to you, state this clearly and calmly to the officer: "I am medically unable to provide this sample due to [condition]. I am not refusing." The officer should record this. You should follow up with medical evidence as soon as possible. Always discuss this scenario with your prescriber in advance if you believe it may apply to you.

At the station: the evidential blood sample

If arrested, you will be asked to provide a blood sample at the police station. This is taken by a medical professional. The sample is divided — one part is sent for laboratory analysis, and one part is offered to you. Always accept your split sample. This allows your legal team to have the sample independently analysed, which can be important to your defence. Again, do not refuse to provide this sample without a documented medical reason.

Always request the duty solicitor at the police station before answering any questions. Access our legal support resources for further guidance and specialist solicitor contacts.

The Field Impairment Test (FIT)

What the FIT is, when police can request it, your right to refuse it, and the critical information CBPM patients must declare.

What is the Field Impairment Test?

Pupil measurement: An officer measures the size of your pupils with a pupillometer. Cannabis (THC) can cause pupil dilation, which may indicate recent use.

Romberg balance test: You are asked to stand upright, tilt your head back slightly, and estimate 30 seconds internally. Tests balance and time perception.

Walk and turn test: You walk heel-to-toe along a straight line, turn, and return. Tests balance, co-ordination, and the ability to follow instructions while performing a physical task.

One-leg stand test: You stand on one leg and count. Tests balance and physical co-ordination.

Finger to nose test: You are asked to touch your fingertips to the tip of your nose with your eyes closed and arms outstretched. Tests fine motor control and proprioception.

You can refuse a FIT — but understand the implications

Unlike refusing a drug swab or blood sample, refusing to undertake a Field Impairment Test is not a criminal offence. You have the right to decline a FIT. However, be aware that a refusal can be noted by the officer and potentially used as evidence of non-cooperation. If you choose to refuse, do so calmly and clearly: "I decline to participate in the Field Impairment Test." You do not need to give a reason, though you may choose to explain relevant medical conditions.

Unlike refusing a drug swab, refusing a FIT is not a criminal offence. You will not be charged for declining to undertake it. However, it is distinct from a drug sample — do not confuse the two.

Declare medical conditions that may affect your FIT performance

This is critically important. Many medical conditions — completely unrelated to drug use — can affect your ability to perform FIT tasks. Before the test begins, clearly inform the officer of any conditions that may affect your performance. These include but are not limited to:

Balance & inner ear conditions

Vertigo, BPPV, Ménière's disease, labyrinthitis, or other vestibular disorders affect balance tests.

Neurological conditions

MS, Parkinson's disease, cerebellar ataxia, peripheral neuropathy, or prior strokes affect co-ordination and balance.

Musculoskeletal conditions

Arthritis, joint replacements, lower limb injuries, or chronic pain conditions affecting standing or walking.

Eye conditions

Nystagmus (involuntary eye movement), glaucoma, or other eye conditions can directly affect pupil measurement results.

ADHD or autism

Attention and executive function differences can affect performance on divided attention tasks.

Other medications

Many prescribed medications (benzodiazepines, opioids, antihistamines, antidepressants) can affect test performance independently of cannabis.

Declare relevant conditions before the FIT begins. Say: "Before this test, I need to inform you that I have [condition], which may affect my performance on some of these tasks. This is separate from any medication I have taken." Ask the officer to record this declaration. If you have supporting medical documentation, tell them you can provide it.

FIT results & what happens next

If a trained Drug Recognition Expert (DRE) or officer trained in FIT concludes there are signs of impairment, this alongside a positive drug test can support a decision to arrest and request an evidential blood sample at the station. The FIT result is one piece of evidence among several — it does not determine guilt. Your declared conditions, prescription history, and blood test results all form part of the overall picture considered by the Crown Prosecution Service.

If you are concerned about FIT performance due to a medical condition, speak to your prescribing clinic in advance. They can provide a letter documenting relevant conditions, which you should carry with your prescription documentation.