Anything that interrupts the breathing pattern or stimulates the vagus nerve. Holding your breath, sipping cold water slowly and swallowing a teaspoon of sugar are the ones with any plausibility.
- Hold your breath for as long as is comfortable, several times.
- Sip cold water slowly, or drink from the far side of a glass.
- Swallow a teaspoon of granulated sugar dry.
- Pull your knees to your chest and lean forward.
None of these have strong evidence. They are harmless, they interrupt the reflex arc in plausible ways, and hiccups nearly always stop on their own within minutes regardless.
Hiccups lasting more than 48 hours are called persistent and should be seen by a doctor. They can indicate an underlying problem and are exhausting in their own right.
A hiccup is an involuntary spasm of the diaphragm followed by the vocal cords snapping shut. Most folk cures either raise carbon dioxide levels or stimulate the vagus nerve, both of which can break the reflex loop.
This is general information, not medical advice, and it does not replace a GP, a pharmacist or NHS 111. Call 999 in an emergency. Full disclaimer.