Stopped by police with a cannabis prescription: what to say, what to carry

This is the encounter every prescribed patient thinks about at least once: blue lights, window down, "have you had anything today?" It matters more than most road-traffic interactions because the roadside test can't distinguish your medicine from an illicit joint. What decides the outcome is what happens in the minute either side of the swab, not the swab itself.

What the officer is actually deciding at the roadside

A traffic stop is a series of small decisions: keep talking or move on, breathalyse, swab, search the vehicle, arrest. The officer works from what they see and what you say. If they smell cannabis, or you mention a prescription, or your eyes look tired, the swab becomes likely — and a positive swab makes arrest likely — regardless of legality. Disclosing early doesn't remove the swab; it changes the officer's frame of reference from "possible impaired driver hiding something" to "prescribed patient with legitimate paperwork".

That frame matters because officers still have discretion around what happens after a positive swab. A patient who's calm, has documents in hand, and clearly wasn't driving erratically often ends up with a "we've noted this, drive on" outcome or a station procedure that's fast and administrative. A patient who says nothing until arrest often gets a much longer, more punitive process, even if the final legal outcome is the same.

The exact sequence, and what to do at each step

Being pulled over

Indicate, stop somewhere safe, turn the engine off, put the interior light on if it's dark, and keep your hands visible on the wheel. Don't reach for documents until the officer's at the window and asks. Say hello, ask what the reason for the stop is, and answer their basic questions (name, address, ownership of the vehicle).

When drugs come up

The moment the officer asks about medications, drugs, or whether you've smoked anything, this is the point to disclose. A calm, complete first sentence covers it:

"I hold a legal prescription for a cannabis-based medicine, prescribed by a specialist for [condition]. I take it as directed. My most recent dispensing label is in the glovebox — would you like to see it?"

That's the whole thing. Don't over-explain, don't apologise, don't ramble about strains or dose. The three facts that matter — lawful prescription, taken as directed, not impaired — are the three limbs of the statutory defence, and you've just named all three.

The roadside swab

If the officer decides to swab, it's the DrugWipe or an equivalent oral-fluid device. It detects THC above a threshold; a positive result means "THC is present at or above the cut-off", nothing more. You can (and should) decline nothing about the swab process — refusing a preliminary drug test at the roadside is a separate offence under section 6A of the Road Traffic Act. Take the test, and if it's positive, expect the next step.

Arrest and station procedure

A positive swab typically means arrest and transport to a station for an evidential blood sample. This isn't a conviction; it's a procedural step. At the station:

• Ask for the custody sergeant to be shown your prescription evidence early. Say clearly you want to rely on the section 5A(3) medical defence.
• You have the right to free legal advice — use it. Ask for a solicitor familiar with drug-driving cases and medical cannabis defences.
• Consent to the blood sample (declining is a separate offence). The blood sample will confirm THC level; your prescription and dosing evidence will be assessed alongside it.
• In interview, keep to the facts: prescription, dose, product, last time taken. Don't speculate.

What to carry in the car — and how

A small evidence pack lives permanently in the glovebox. Digital versions on your phone are legally fine, but paper is faster to hand over and doesn't require you to unlock a device in front of an officer.

1. The most recent dispensing label or a printed prescription copy — showing your name, the product, dose, and prescribing clinic.
2. A clinic letter confirming you are a current patient and the medication is prescribed for a named condition. Ask your clinic if they don't provide one.
3. Prescriber contact details so the officer can verify quickly if they choose to.
4. The medication itself in its original packaging, if you're carrying it — never decanted into a nondescript container.

What impairment actually means

The statutory defence has three limbs, and the one patients underestimate is the third: your driving wasn't impaired. The medical defence protects you from the strict-liability THC-limit offence; it doesn't protect you from the older section 4 offence of driving while unfit through drugs.

Practically: don't drive within the window your prescriber tells you not to; don't drive if you feel sedated, slowed, or dose-adjusted; don't combine your medicine with anything else that affects driving. If your product is a night-time strain and you take it at bedtime, don't drive at 7am if you still feel foggy. Prescribers usually give a "wait X hours" figure — respect it and, if in doubt, wait longer.

After the stop

Whether it ended with "drive on" or arrest, write it down: date, time, location, officer's badge number if you have it, what was said, what tests were done. If you're facing charges, that record and your clinic letter go to your solicitor first thing.

For the underlying law, see the medical cannabis driving pillar and whether to tell the DVLA.