ALL THINGS LICENSING
Clinicians and patient groups widely advise that drivers taking medication containing THC should avoid driving for at least 4 to 6 hours after dosing because of slowed reaction times, reduced coordination, and difficulty concentrating.
The DVLA position: No direct guidance medicinal cannabis
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Most, if not all, licensing authorities have adopted the DVLA Group 2 Medical Standards for licence holders as is considered best practice and in line with the duty to ensure that a person remains physically and mentally ‘fit’ to carry out their duty of driving fare paying passengers.
However, despite cannabis-based medicines being legal since 2018, the DVLA has not released specific Group 2 guidance for drivers prescribed CBPMs. The official document, Assessing Fitness to Drive, contains no dedicated section on cannabis-based medicines, even in its latest update (Nov 2025).
The DVLA has confirmed through Parliamentary written answers that:
l Drivers must notify DVLA if their underlying medical condition affects safe driving.
l Prescribers are expected to advise patients not to drive when impaired.
l Driving over the drug driving limit is still an offence for both illicit and medically prescribed cannabis if impairment is present.
It is also possible that any underlying condition which CBMPs are designed to treat may also mean that the licence holder doesn’t meet the group 2 standard. One of the examples cited was a driver suffering from PTSD which would mean the removal of the Group 2 entitlement from a licence holder, unless:
l PTSD does not impair driving, and l They have no flashbacks, dissociation, panic attacks, or unpredictable symptoms, and
l They are clinically stable, and l Their medication does not cause impairment, and l DVLA/the licensing authority receives any required evidence and clearance
Applying comparable DVLA standards: the ‘methadone benchmark’
Because the DVLA provides no specific rules on medicinal cannabis for vocational drivers, many licensing authorities have been confused about how to respond to this scenario when it presents itself.
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In Guildford I’m lucky to have engaged a GP to assist in us determining whether an applicant is medically fit based on their records. Our medical advisor has, in the absence of formal guidance from the DVLA, suggested using the closest comparable category: methadone and similar controlled substances used in treatment. Methadone is a substitute for heroin however is still a dependant drug and can still lead to impairment, much like cannabis.
Under DVLA Group 2 standards for drug misuse/ dependence, drivers on methadone must show:
l Long term (at least 3 year) stability l No impairment, and l Sustained compliance with treatment
Group 2 drivers misusing or dependent on drugs are subject to stringent restrictions and cannot drive until medical evidence demonstrates stability and control.
While medicinal cannabis is not equivalent to methadone treatment, both involve psychoactive substances that may impair driving performance. As a result, our medical advisor has recommended applying a multi-year stability requirement for CBPM users before deeming them fit under Group 2.
This means any new applicant would be required to show that for the past 3 years they have been using medicinal cannabis and are stable. For existing licence holders with a prescription, the revocation of a licence should be expected until they can demonstrate compliance with the 3-year stability period.
Driving impairment: What the evidence shows
Research commissioned by the DfT identifies clear risks associated with medicinal cannabis:
l THC can impair reaction time, coordination, and concentration.
l Impairment varies between users and may last hours beyond peak therapeutic effect.
l Prescribers and patients often underestimate impairment risk.
This aligns with guidance from patient groups and clinics warning that THC remains detectable for hours to days and that impairment windows depend on dose, frequency and individual tolerance.
For taxi and private hire drivers who are responsible for passengers, other road users, and often operate long hours, these impairment risks carry additional safety consequences.
MARCH 2026 PHTM
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