Patients who complain of diarrhoea may describe a frequent urge to pass stools that may be loose and poorly formed rather than watery. The main drug used for these symptoms is the antimotility agent loperamide, which is used on an occasional, short-term basis to reduce diarrhoea or urgency of defaecation.

For use in IBS it is licensed for people age 18 years and over, only where the diagnosis has previously been made by a doctor. The dose is two capsules (4mg) taken initially, followed by one capsule (2mg) after every loose stool. The maximum daily dose should not exceed eight capsules (16mg) under pharmacist supervision and a doctor should be consulted if taken for longer than two weeks.

Some patients titrate use according to variation in their symptoms. The limited evidence available suggests that loperamide reduces frequency of bowel movements, but not abdominal pain or distension.

An obvious side-effect is constipation. It is usually trouble-free but dizziness, headaches, flatulence and nausea are sometimes seen. Rarely abdominal pain, drowsiness, dry mouth, dyspepsia, rash and vomiting are reported.

Users should be advised not to exceed the recommended daily dose or duration as cardiac arrhythmias have been reported in association with overdose.