Bismuth subsalicylate (Pepto-Bismol): what it treats, who should avoid it and why

Bismuth subsalicylate is the active ingredient in Pepto-Bismol, a pink liquid and chewable tablet familiar from American pharmacies and also sold in the UK. The NHS describes it as a medicine that treats symptoms of indigestion, heartburn and diarrhoea, and says it can be bought from pharmacies and shops without a prescription.

It is used for indigestion, acid reflux and heartburn, feeling sick, and diarrhoea. The NHS explains that it works by reducing inflammation and forming a protective coating in the stomach, the lower part of the food pipe and the gut.

The name tells you something important: salicylate is the same family as aspirin. That is the reason for several of the safety warnings below, and why it should be treated with a little more care than a simple antacid.

The NHS says Pepto-Bismol usually comes as a liquid you swallow or tablets you chew, and that you can take it with or without food. For the liquid (17.5 mg/ml oral suspension) it advises shaking the bottle, taking 30 ml at a time using the dosing cup, waiting at least 30 minutes between doses and not taking more than 8 doses in 24 hours. For the 262.5 mg chewable tablets it advises chewing 2 tablets, or dissolving them in the mouth, waiting at least 30 minutes between doses and not taking more than 16 tablets in 24 hours.

It also gives a firm limit on time: do not take Pepto-Bismol for more than 2 days unless advised by a doctor, and stop and see a GP if symptoms get worse or do not get better. Always check the packet or leaflet, as products and strengths differ.

If you take too much, the NHS says it is important to get medical advice, because it can be dangerous. Speak to a pharmacist as soon as possible if you have taken more than the packet says or if you start hearing ringing or buzzing in your ears (tinnitus), which is a recognised sign of too much salicylate. If you cannot speak to a pharmacist, or took too much on purpose, call NHS 111.

The NHS lists black poo and a black tongue as common side effects, and says they are harmless and usually go away on their own. This is useful to know, because black stools can otherwise signal bleeding from the upper gut. If you have black poo and have not taken bismuth, or if it is tarry and very smelly, or you have other symptoms such as vomiting blood, that is a different matter: the NHS stomach ulcer advice says to call 999 or go to A&E for vomit that looks like ground coffee or poo that is black, sticky and very smelly.

In rare cases a serious allergic reaction can occur. The NHS says symptoms include a swollen throat or tongue, a raised itchy rash and difficulty breathing, and to call 999 if you think you might be having anaphylaxis. Report side effects through the Yellow Card scheme.

The NHS says it will not usually affect your ability to drive, ride a bike or use machinery, and you can eat and drink as usual while taking it.

Most people aged 16 or older can take Pepto-Bismol. The NHS says not to give it to children aged 15 or under because it can cause a serious condition called Reye’s syndrome in rare cases. This is the same reasoning that applies to aspirin in children.

It may not be suitable if you have had an allergic reaction or serious side effect from bismuth subsalicylate or from aspirin before, have blood in your poo, have a blood clotting disorder, have gout, or have a stomach ulcer. Read the leaflet and speak to a pharmacist or doctor if unsure.

It is not usually recommended during pregnancy or breastfeeding, and the NHS says to talk to a doctor or pharmacist before taking it in either situation, as they may be able to recommend a different medicine.

Because it contains a salicylate, it may not mix well with several medicines. The NHS lists non-steroidal anti-inflammatory drugs such as aspirin and ibuprofen, anticoagulants such as warfarin and apixaban, methotrexate, some antibiotics such as doxycycline, some antidepressants, and some medicines for gout and diabetes.

The point of those warnings is the combination of salicylate with drugs that also affect bleeding, the stomach lining or kidney handling. If you take any regular medicine, particularly a blood thinner or methotrexate, check with a pharmacist before using it, even for a short time.

The NHS says most people have indigestion at some point and it is usually not serious. Helpful steps include cutting down on tea, coffee, cola and alcohol, raising your head and shoulders in bed, losing weight if you are overweight, not eating 3 to 4 hours before bed, avoiding rich, spicy or fatty foods, not taking ibuprofen or aspirin unless prescribed, and not smoking. A pharmacist can recommend antacids, alginates or proton pump inhibitors.

See a GP if you keep getting indigestion, are in severe pain, have lost a lot of weight without meaning to, have difficulty swallowing, keep being sick, have iron deficiency anaemia, feel a lump in your stomach, or have bloody vomit or poo, the NHS says. These can be signs of something more serious.

For heartburn that happens most days, or if lifestyle changes and pharmacy medicines are not helping, the NHS says to see a GP, who can offer alternative or stronger treatments and look for other causes. A short course of a medicine like this is not a substitute for finding out why symptoms keep returning.

Pepto-Bismol is bought over the counter, so most decisions are made with a pharmacist. A GP, NHS or private, would assess recurrent or persistent symptoms. Ask a pharmacist to check it against your regular medicines.