Fainting after drinking alcohol: what to know

Fainting after drinking alcohol can result from dehydration, low blood sugar, a blood-pressure drop or a heart problem. Alcohol can also make it harder to notice dizziness and can increase the danger of falls, vomiting and head injury. One episode deserves attention, particularly if the amount was small or the cause is unclear.

Alcohol may increase urination and leave you short of fluid. Drinking instead of eating can contribute to hypoglycaemia, while heat, standing and medication can add to a pressure drop. Anaemia and abnormal rhythms such as atrial fibrillation are alternative explanations, not conclusions from the symptom alone. A healthcare professional may review your pulse, blood pressure, blood tests, heart tracing, medicines and pattern of alcohol use.

Check that the person is breathing. Lay them flat with legs raised, or place them on their side if they are drowsy or vomiting. Keep them supervised and do not make them walk, shower or drink anything while they are not fully alert. When awake and swallowing normally, offer small sips of water and food if appropriate. Stop alcohol for now and do not drive or operate machinery after the episode.

Call emergency services for slow or abnormal breathing, inability to wake, a seizure, chest pain, severe confusion, a major fall or new weakness. Seek urgent medical assessment if fainting happened during exercise, followed palpitations, occurred more than once, or involved black or bloody vomit or stool. A medical review is sensible after a first faint, even when alcohol seems to be a trigger.

Could alcohol have interacted with a prescription or caused a pressure change? Do I need an ECG or blood tests? What symptoms mean I should call emergency services next time?