When to worry about diarrhoea with hyperthyroidism

Excess thyroid hormone can speed up movement through the digestive system, leading to frequent stools or diarrhoea. It may occur alongside heat intolerance, sweating, tremor, anxiety, weight loss, difficulty sleeping or a fast heartbeat. Diarrhoea may also come from infection, food triggers or medicine, so a new or changed pattern should not automatically be attributed to the thyroid.

Replace fluids with regular sips of water and consider oral rehydration solution if stools are frequent. Keep a note of stool changes, palpitations, temperature sensitivity and any thyroid medicines. Take prescribed treatment exactly as directed and do not change the dose or stop it because of diarrhoea without medical advice.

Get urgent help for chest pain, fainting, confusion, severe breathlessness, a very fast or irregular heartbeat, severe weakness, inability to drink, very little urine, blood in the stool or intense abdominal pain. Arrange prompt review when diarrhoea persists, is worsening, or appears with escalating tremor, fever, sweating or palpitations.

Ask whether your thyroid levels and treatment need checking, whether another cause of diarrhoea should be investigated, and which fluids or medicines are appropriate. Bring your medicine list and describe how quickly symptoms began and whether your heartbeat feels different.