Alcohol, Drugs, and Fitness to Ride
Riding demands coordination, judgement, and reaction time - all of which alcohol and drugs degrade first and most. Alcohol reduces inhibition while impairing skill, so riders often feel more confident exactly when they are less capable. It slows reactions, narrows attention, and distorts distance and speed perception. There is no safe amount before riding; the only reliable rule is not to drink if you will ride. The same applies to recreational drugs and to many prescription and over-the-counter medicines, especially antihistamines, strong painkillers, and sedatives, which can cause drowsiness.
Fitness is broader than substances. Fatigue is a major killer: tiredness slows reactions much like alcohol. Illness, emotional stress, and some medical conditions also affect your ability to ride safely, and some conditions must be declared to the licensing authority. If you feel unwell, drowsy, or emotionally unfit to concentrate, do not ride. If you are taking a new medicine, read the label and ask a pharmacist whether it affects driving.
Trap: questions may offer "drink coffee" or "wait an hour" as fixes for alcohol. Only time removes alcohol, and the safest answer is not to ride at all. Rule of thumb: if you would not trust yourself to perform a precise task, do not ride. Worked example: you had two drinks at lunch and feel fine at 6pm. Feeling fine is not a measure of blood alcohol; arrange another way home rather than relying on your judgement.