Diarrhoea before your period: what to know

Some people notice faster bowel movements or loose stools in the days before menstruation as hormone shifts affect the bowel. The pattern is more suggestive of a cycle-related change when it begins at a similar point each month and settles after bleeding starts. Food poisoning, gastroenteritis and food intolerance can begin at any point. Coeliac disease, Crohn's disease, irritable bowel syndrome, giardiasis and hyperthyroidism may cause symptoms that continue outside the premenstrual window, so timing alone cannot diagnose the cause.

Drink regularly and replace fluids after loose stools. Keep meals simple if your stomach feels unsettled, and reduce foods, alcohol or caffeine that you have noticed make symptoms worse. A diary covering several cycles can record stool changes, cramps, bleeding, medicines, stress and meals. Gentle heat may ease period cramps. Avoid taking new medicines or repeated anti-diarrhoeal treatment without checking that it is appropriate for you.

Arrange a medical review if diarrhoea is new, severe, lasts beyond the period, wakes you repeatedly, or disrupts daily life. Seek urgent help for blood or black stool, severe abdominal pain, fainting, confusion, repeated vomiting or signs of dehydration such as very little urine and a dry mouth. Also mention heavy or unusual bleeding, pain between periods, fever or possible pregnancy.

Ask whether your cycle diary supports a hormonal pattern, whether testing is needed, and which options can relieve diarrhoea and period pain safely.