Why does irritable bowel syndrome cause diarrhoea?

Diarrhoea is a very common presentation of Irritable Bowel Syndrome. Faster movement gives the large bowel less time to absorb water, so stools may be loose or urgent. IBS can also make the gut more sensitive, which can amplify cramps and the need to find a toilet quickly. Some people notice episodes after certain meals, during stress, or when their daily routine changes. Others alternate between diarrhoea and constipation.

Drink fluids regularly, particularly if stools are frequent, and choose simple meals that you tolerate while symptoms settle. Keep notes on meals, caffeine, alcohol, stress and bowel changes instead of removing many foods at once. A clinician or pharmacist can advise on medicines for diarrhoea and whether they are suitable for you. If a specific food seems troublesome, discuss a structured dietary approach with a qualified professional.

Seek medical advice if diarrhoea is new, persistent, wakes you from sleep, or differs clearly from your familiar IBS pattern. Get urgent help for severe abdominal pain, fainting, confusion, signs of dehydration, blood or black stool, fever, repeated vomiting, or unexplained weight loss. These symptoms can indicate a problem that needs assessment beyond IBS.

Ask whether your symptoms match diarrhoea-predominant IBS, which medicines are appropriate for occasional or ongoing episodes, and whether any medicines you already take can affect your bowel habits. Bring your symptom record if you have one.