Loperamide (Imodium): diarrhoea treatment explained

Loperamide is an anti-motility medicine, sold as Imodium and under pharmacy own-brand labels. The NHS lists short-term diarrhoea, diarrhoea from irritable bowel syndrome, recurring diarrhoea caused by Crohn's disease, ulcerative colitis or short bowel syndrome, and colostomy management.

Several presentations exist: standard capsules and tablets, dissolving tablets such as Imodium Instants, and Imodium Plus products that add simeticone for wind and cramps.

Diarrhoea happens when food and fluid rush through the gut too fast for water to be absorbed. Loperamide slows that transit, giving the body longer to draw water back in, so poo becomes firmer and you go less often. It does not clear an infection or fix the cause; it manages the symptom.

The NHS says improvement usually begins within an hour. Most people use it for a day or two.

For adults with short-term diarrhoea the NHS describes a usual start of 2 capsules or tablets straight away, then 1 after each further runny stool, up to 6 a day for over-the-counter supply or 8 on prescription. For long-lasting diarrhoea prescribed to adults, 2 to 4 a day spread through the day is typical, up to 8, adjusted by the doctor. Always go by the label or prescriber.

Swallow it whole with water, with or without food. Children under 12 should only have it if prescribed.

• Do not use it for more than 48 hours without medical advice if you bought it yourself.

• If you miss a dose, take the usual dose after your next runny stool and do not double up.

• One extra dose once is unlikely to harm. Higher doses can cause serious heart problems; call NHS 111 if you have taken two or more extra or notice an irregular heartbeat.

• Keep drinking fluids, and ask a pharmacist for advice if you see signs of dehydration such as passing less urine or dark urine.

Over the counter, loperamide is for anyone aged 12 or over with short-term diarrhoea, and for adults from 18 with IBS-related diarrhoea once a doctor has diagnosed IBS. Children aged 11 and under and adults with long-term diarrhoea need a prescription.

It should be avoided during severe diarrhoea after antibiotics, a flare of ulcerative colitis or other inflammatory bowel disease, or when you are constipated or your abdomen is swollen. Speak to a doctor first if diarrhoea has lasted beyond 48 hours, if you have liver problems or HIV with a swollen stomach, or if you are pregnant, planning pregnancy or breastfeeding.

For IBS, recent bloody stools, nausea or vomiting, appetite or weight loss, a high fever, painful urination, recent foreign travel and being 40 or over with a gap since your last IBS episode all call for a medical check.

Common effects are constipation, nausea, headache and wind. If constipation develops, stop taking it and increase fibre and water.

Stop the medicine and call NHS 111 for faintness, reduced alertness or loss of consciousness, clumsy movements, stomach pain or tenderness with a fever, fast pulse or vomiting (possible inflammation of the pancreas), severe constipation, or difficulty passing urine. Call 999 for swelling of the lips, mouth, throat or tongue, breathing difficulty or collapse.

Suspected side effects can be reported to the Yellow Card scheme.

Loperamide is not usually recommended in pregnancy because safety data are limited, and a doctor will weigh benefits against risks. It is safe while breastfeeding, as only tiny amounts reach milk. There is no evidence of an effect on fertility.

Medicines the NHS names include clozapine, ritonavir, quinidine, itraconazole, gemfibrozil, desmopressin and other medicines for the gut. If severe diarrhoea develops while you take metformin, blood pressure tablets or heart failure medicines, a doctor may advise pausing them temporarily; do not decide this yourself.

The NHS says it is best not to drink alcohol with loperamide, since both can cause drowsiness, dizziness and poor concentration. If you feel dizzy, tired or drowsy, do not drive, cycle or use machinery or tools until you feel better.

You can eat normally, although fatty or spicy food is best avoided while diarrhoea lasts. Contact a doctor if diarrhoea continues past 48 hours or if you are thinking of using loperamide to prevent diarrhoea.