What actually prevents and treats travellers' diarrhoea, by the guideline evidence

For treating travellers' diarrhoea, the expert-consensus evidence is clear: antibiotics work in most moderate-to-severe cases, while mild cases can usually be managed with fluids and an anti-motility drug such as loperamide, or with bismuth subsalicylate [s1]. For preventing it, the picture is messier — routine antibiotic prophylaxis is generally not recommended for most travellers, and the popular habit of taking Pepto-Bismol to ward it off rests on decades-old studies that a 2025 randomised trial was unable to confirm [s1] [s2]. None of this is a prescription, and the drug choices below are guideline positions, not instructions.

The most common illness of international travel

Travellers' diarrhoea is the single most common travel-related illness, and while it is usually self-limiting, it causes real morbidity — lost travel days, occasional lasting sequelae, and, at a population level, a route by which multidrug-resistant bacteria spread [s1]. That last point is why current guidance is more cautious about antibiotics than it once was: every course of antibiotics a traveller takes is also an opportunity for resistant organisms to be selected and carried home [s1].

What the guideline actually recommends

In 2017 an expert panel convened by the International Society of Travel Medicine produced a graded consensus guideline — a critical appraisal of the literature that issued 20 graded recommendations across prophylaxis, diagnosis, therapy, and follow-up, plus three non-graded consensus statements [s1]. The panel also introduced new definitions of severity, shifting the framework away from simply counting stools toward how much the illness disrupts the traveller's activity [s1].

On treatment, the panel found that strong evidence supports the effectiveness of antimicrobial therapy in most cases of moderate to severe travellers' diarrhoea [s1]. For milder illness, the guidance is deliberately more conservative: either increasing fluid intake alone, or using loperamide or bismuth subsalicylate, may suffice for most mild cases, without reaching for an antibiotic at all [s1]. The logic is proportionality — match the intervention to the severity, and reserve antibiotics for the cases where the benefit clearly outweighs the resistance risk.

Prevention is where the evidence gets weak

The prevention question is where popular practice and evidence drift apart. The guideline does not endorse routine antibiotic prophylaxis for the average traveller, and it explicitly flags gaps in what is known about the individual, community, and global health risks of acquiring multidrug-resistant organisms during travel [s1].

Bismuth subsalicylate — the pink liquid sold as Pepto-Bismol — is a specific case worth dwelling on, because taking it preventively is a widespread traveller habit. It is indicated for treating travellers' diarrhoea, but its use to prevent the illness is off-label, resting on studies from the 1980s that carry real limitations [s2]. A 2025 double-blind, placebo-controlled randomised trial set out to test it properly: 270 travellers heading to Southeast Asia, South Central Asia, North Africa, or sub-Saharan Africa were randomised to bismuth subsalicylate — four tablets twice daily, 2.1 grams in total — or placebo [s2]. There was no significant difference between the groups in loose stool or diarrhoea, although the trial did not reach its target sample size and so could not rule a benefit out either [s2]. The authors' own summary is the honest one: this is the first new data on the question since the 1980s, and it should not be read in isolation as proof of either effect or no effect — larger studies are needed to see whether some travellers benefit under some conditions [s2].

What holds and what doesn't

The claims that hold up are the treatment ones: antibiotics for moderate-to-severe illness, and fluids with loperamide or bismuth for mild illness, all from a graded expert guideline [s1]. The claim that wobbles is preventive bismuth — a habit far more confident than its evidence, now tested once in a modern trial that could not confirm it [s2]. And the claim that has actively shifted is routine antibiotic prophylaxis, which the guideline steers most travellers away from, partly because of the resistance it can breed [s1].

For an individual traveller, the useful implications are indirect. The specifics — whether to carry a standby antibiotic at all, which one, and when it would be appropriate to use it — depend on the destination, the length of stay, and the person's own health, and they are exactly the questions a pre-travel consultation exists to answer. This article describes what the evidence says; it does not tell any reader what to pack or take.