Alcohol, Drugs & Fitness to Drive

Scanning for developing hazards and telling static from moving hazards only works if the driver doing it is actually capable of it. Alcohol, drugs, tiredness, and illness all reduce the same things this module has been building: how early you notice a change, how well you judge distance and speed, and how quickly you can react once you have.

Alcohol affects judgement, reaction time, and coordination well before a driver notices anything is wrong — in fact, one of the things it impairs first is the ability to judge your own performance accurately, so feeling confident is not evidence of being safe to drive. The only amount of alcohol that removes the risk entirely is none, which is why the simplest working rule is: if you're driving, don't drink.

Driving while impaired by a drug is an offence whether that drug is illegal, prescribed by a doctor, or bought over the counter. Illegal drugs — including cannabis and cocaine — can be tested for at the roadside, alongside the breath test for alcohol. But legal medicine can impair you just as seriously: some prescription and pharmacy medicines — certain painkillers, sleeping tablets, and antihistamines among them — cause drowsiness or slow reaction time for hours after you take them. Combining any of these with alcohol multiplies the effect rather than adding to it.

Fatigue reduces reaction time and concentration in a way that closely mirrors alcohol, and it can arrive gradually enough that you don't notice it building. Warning signs include yawning repeatedly, drifting within your lane, and losing track of the last few minutes of the drive. General Highway Code advice for long journeys is to take a proper break roughly every couple of hours — not a legal limit, just sound practice. Illness works the same way: if you feel unwell, or your symptoms or medication are likely to affect concentration, treat it as a reason not to drive, not just an inconvenience.

You must be able to meet the legal eyesight standard every time you drive, and certain medical conditions have to be reported to the licensing authority rather than managed quietly on your own — this is a legal duty, not just good sense. The exact eyesight standard and the notification process are covered in full in Your Provisional Licence & the Eyesight Rule (linked below) — the short version here is that fitness to drive includes your eyes and your health, not just what you had to drink.