There are endless medical problems that can affect your ability to drive safely - both temporary and permanent. Failing eyesight; poor balance or coordination; issues with memory or concentration; lack of muscle strength or control; reaction times; pain and drowsiness - all can affect your safety on the road.
When we think about people who aren't fit to drive, most of us think first of older people. But their reputation as unreliable drivers may be unfair - the evidence that older people are less safe at all is weak. There are half a million 17- to 19-year-olds with driving licences - that's one in 65 drivers - and they account for about one in 17 accidents.
By contrast, there are seven times more older drivers and one in 10 accidents in this age group. So older drivers actually have far fewer accidents than young people per head of population. However, it's important to recognise that these figures might be skewed by the fact that older people tend to drive far fewer miles. There's no upper age limit for driving a normal car, but over-70s must reapply for a licence every three years.
If you have any long-term condition that could affect your driving, it's up to you to let the DVLA know. You'll need to keep your insurance company up to date, too: your insurance could be invalid if you don't. Your doctor can tell you if you could be affected.
Epilepsy is perhaps the most obvious medical reason people shouldn't drive - seizures can sometimes cause complete loss of consciousness with no warning. So everyone with epilepsy must inform the DVLA and as a rule, you're not allowed to drive until you have been seizure-free for at least a year (six months after the first seizure in some cases).
Blackouts are very common - one in three A&E attendances are due to loss of consciousness, and it's thought two to three times more accidents are due to blackouts than seizures. If you have a blackout while sitting, you'll usually need to let the DVLA know - check with your doctor.
If it's a simple faint while you're standing you don't need to tell them and can keep driving. However, if there's no obvious reason for the blackout, you must tell the DVLA. They'll send a questionnaire with more information and you may need medical reports. You won't be able to drive until one, six or 12 months after your last blackout, depending on the circumstances. Again, your GP or consultant can advise.
Multiple sclerosis, motor neurone disease, Parkinson's disease and other conditions affecting your nervous system can all affect your ability to drive. Again, you'll have to fill in a questionnaire and you may be given a licence for a limited time.
Having a stroke or a TIA (the same symptoms as a stroke, but going away on their own within 24 hours) doesn't necessarily mean you won't be able to drive again. In fact, while you mustn't drive for at least a month, you don't need to tell them unless you still have weakness or eyesight problems after that. However, if your stroke was caused by a brain tumour or other brain problem, you do need to inform them - your doctor can advise you. If you have multiple TIAs, you mustn't drive and do need to tell the DVLA. You can start driving again once three months have passed since your last TIA.
Having angina which comes on at rest, when you're driving or when your emotions are high means you mustn't drive. You're allowed to start driving again once your angina is controlled.
Particularly ones on your tummy or legs - render you unfit to drive until you've recovered. The deciding factor is often not whether you're fit to drive normally, but whether you could perform an emergency stop safely. Ask your team about the regulations for your procedure before you leave hospital.
Some medications can make you drowsy, so it's important to check with your pharmacist if you're in doubt. Among the most common medicines involved are strong 'opioid' painkillers; tranquillisers like benzodiazepine; and some antidepressants. Insulin and 'sulfonylurea' tablets for diabetes can cause dangerous low blood sugar - always check the driving regulations with your doctor.