3 Clinical psychopharmacology3.4 Therapeutics
3.4.9 Advice on driving and other complex behaviours
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Written by Resident Doctor Committee · Published
Assessing fitness to drive
Assess illness, medicines, substance use, sleep and physical health together, because self-assessment alone is not enough.
Group 2 standards for buses and lorries are stricter than Group 1 standards for cars and motorcycles.
Medicines that impair driving
Benzodiazepines carry the greatest driving risk among psychotropic drugs, through sedation, slowed reaction time and residual next-day effects.
Benzodiazepine risk is highest when people start the drug or raise the dose.
Dopamine agonists can cause sudden sleep without warning.
H1 antihistamine | Example | Effect on driving |
|---|---|---|
First-generation | Chlorphenamine | Lipophilic, so they enter the brain and sedate |
Second-generation | Cetirizine, loratadine | Largely do not sedate |
Alcohol and other sedatives add to the impairment.
Licensing and confidentiality
Patients must notify the Driver and Vehicle Licensing Agency (DVLA), which decides fitness.
If a patient keeps driving against advice and endangers others, General Medical Council (GMC) guidance supports disclosure to the authority's medical adviser.
Drug driving law
Driving while unfit through drugs is an offence, even with prescribed medicines.
A separate offence covers specified drugs, such as methadone and several benzodiazepines, above legal blood limits, without proof of impairment.
The statutory medical defence covers only the limit offence, when the medicine was lawfully supplied and taken as directed.
Other complex behaviours
Dopamine agonists and aripiprazole can cause gambling, compulsive spending, hypersexuality and binge eating.
Hypnotics can cause sleepwalking, sleep eating or sleep driving with incomplete recall.