Written for Stock My Medicine and clinically reviewed by Hajra Dhanchora, MPharm (GPhC 2216990).
Diarrhoea is the body flushing something out, which is useful for a day and miserable after that. Most cases are a stomach bug or something you ate, last under a week, and need nothing more than fluids and patience. But there's a right way to rehydrate, a right time to take a tablet that stops it, and a short list of situations where stopping it is the wrong move. Here's the lot.
How long does diarrhoea last?
In adults and children, diarrhoea from a stomach bug usually stops within five to seven days; vomiting that comes with it is usually over in a day or two. Food poisoning tends to be shorter and sharper. The first 24 to 48 hours are the worst, and the stools then gradually firm up over several days. Diarrhoea that lasts more than a week in an adult, or that keeps coming back, needs a GP to look for a cause rather than another box of tablets.
What causes it?
The common ones: a viral stomach bug (norovirus, rotavirus in children), which also brings vomiting and spreads through a household in days; food poisoning from bacteria such as campylobacter or salmonella, usually 1 to 3 days after the meal; antibiotics, which upset the gut bacteria in up to one in three people taking them; stress and anxiety, which speed the bowel up; too much alcohol, caffeine, sorbitol in sugar-free sweets, or fructose; and travel, where a change of bacteria does it. Persistent or recurring diarrhoea has a different list: irritable bowel syndrome, coeliac disease, lactose intolerance, inflammatory bowel disease, an overactive thyroid and some medicines, including metformin and magnesium antacids.
How to stop diarrhoea: the two jobs
The first job is to replace what you're losing; the second, optional, is to slow the bowel down.
1. Rehydrate properly
Water alone isn't enough once you've had several loose stools, because you're losing salts and sugar with the fluid, and plain water without them is absorbed poorly. An oral rehydration sachet such as Dioralyte has the right balance; make it up with the exact amount of water on the pack, and sip a glass after each loose stool. For adults who'd rather improvise, diluted squash with a pinch of salt is closer to the mark than sports drinks, which are too sugary. Small sips, often, beat a pint in one go, which tends to come straight back. Children should keep drinking their usual milk or formula between rehydration drinks; don't water formula down.
2. Loperamide, when it's appropriate
Imodium (loperamide) slows the bowel and firms stools within an hour or two. It's the right choice when you need to function: a journey, a work day, a wedding, or diarrhoea that's exhausting you. Adults and over-12s only: two capsules to start, then one after each loose stool, up to eight a day, for no more than two days without advice. Instant Melts dissolve on the tongue with no water; Dual Action adds simeticone for the cramps and wind. Don't take it if you have a fever, blood or mucus in the stool, or diarrhoea that started during or just after antibiotics, because in those cases the bowel needs to clear the infection, and holding it in can make things worse. Not for children under 12 without a doctor's say-so.
What to eat when you have diarrhoea
Eat as soon as you feel like it; starving yourself doesn't shorten a bug and leaves you weaker. Start with small, plain, frequent meals: toast, rice, bananas, plain pasta, boiled potatoes, crackers, soup, a boiled egg. Add normal food back over a day or two. Skip fatty, fried or spicy food, large amounts of fruit and fruit juice, sweeteners, caffeine and alcohol until the stools are formed. Dairy is fine for most people, though some find milk makes it worse for a week or so after a bug and can swap to lactose-free. Probiotics from a supplement or live yoghurt may shorten infectious diarrhoea by about a day and help after antibiotics.
How long to stay off work or school
Until you've had no diarrhoea or vomiting for 48 hours. That's the NHS rule for adults and children, and it's there because you're still shedding virus after you feel better. Stomach bugs spread on hands and surfaces: wash hands with soap after every toilet visit and before food (alcohol gel doesn't kill norovirus), use your own towel, wash soiled clothes and bedding at 60°C, and stay away from swimming pools for two weeks after. Don't prepare food for other people until you're clear.
Diarrhoea in children and babies
Children dehydrate faster than adults because they're smaller and lose proportionally more. The job is the same, fluids first, but the thresholds are lower: offer a rehydration drink after every loose stool, keep breastfeeding or formula going as normal, and don't give loperamide to anyone under 12. Stick to plain food they'll accept, and don't worry about a day of eating little as long as they're drinking. Rotavirus is the usual culprit in under-fives, and the vaccine babies get at 8 and 12 weeks has made severe cases much rarer. A child who is listless, has a dry mouth, no tears, or hasn't passed urine for eight hours needs assessing the same day; a baby under six months with diarrhoea should always be seen.
Signs of dehydration: when to call 111
| Call 111 if | Call 999 or go to A&E if |
|---|---|
| You're passing little or very dark urine, dizzy when you stand, or can't keep fluids down; you're still unwell after a week; a baby has fewer wet nappies, a dry mouth, sunken eyes or is drowsy; a child has had six or more loose stools or three vomits in 24 hours; you're over 65, pregnant, or have a weakened immune system or a long-term condition such as diabetes | Vomiting blood or something that looks like coffee grounds, green vomit, blood in the stool, severe constant tummy pain, a stiff neck with light hurting the eyes, confusion, or someone who is very drowsy or breathing fast |
Babies under six months with diarrhoea should be seen the same day. Everything above is in our digestive health collection, and our pharmacist can advise if you're on other medicines, since diarrhoea can stop tablets such as the contraceptive pill and some heart medicines being absorbed.
Frequently asked questions
How can I stop diarrhoea immediately?
Loperamide is the only thing that works within hours, and only for adults without the red flags above. Everything else, fluids, plain food, rest, supports recovery rather than stopping the next trip.
Does Imodium make it last longer?
For ordinary viral diarrhoea, no; studies show it shortens the course. The exception is bacterial infections with fever or blood, where you should let it run.
Can stress cause diarrhoea?
Yes. The gut and brain share wiring, and nerves speed the bowel up. If it's a pattern, it's worth reading about IBS.
Why do antibiotics give me diarrhoea, and what helps?
They clear the gut bacteria that keep things balanced. Finish the course, drink plenty, consider a probiotic, and see a GP if it's severe or has blood in it, which can signal a C. difficile infection.