Acute gastroenteritis remains one of the most common reasons young children end up in emergency departments worldwide. The illness, usually viral, produces vomiting and diarrhea that can rapidly dehydrate a small body. The cornerstone of treatment is oral rehydration therapy, a carefully balanced solution of salts and sugars. The problem is that persistent vomiting often defeats oral rehydration before it can work, forcing clinicians toward intravenous lines, hospital admission, and prolonged distress. Ondansetron, a selective serotonin 5-HT3 receptor antagonist originally developed for chemotherapy-induced nausea, blocks the signaling pathway that triggers the vomiting reflex at the level of the gut and the brain’s vomiting center. Its adoption in pediatric emergency care has grown steadily, but the evidence base has needed updating.

The previous comprehensive meta-analysis on the question was published in 2020, and the research team identified three specific gaps it left open. It could not incorporate a subsequently published trial of multidose ondansetron given after hospital discharge, it did not evaluate the volume of oral rehydration solution children actually tolerated, and it did not formally explore sources of statistical heterogeneity through meta-regression. The new analysis, conducted and reported according to the PRISMA 2020 statement and guided by the AMSTAR 2 appraisal tool, set out to close those gaps. The researchers searched PubMed, CENTRAL, ScienceDirect, Google Scholar, and ClinicalTrials.gov through June 2026, and assessed risk of bias with the Cochrane RoB 2 tool and certainty of evidence with GRADE.

The headline results are striking in their consistency across measures of vomiting morbidity. Compared with placebo, ondansetron reduced the risk of ongoing vomiting by more than half, with a pooled risk ratio of 0.48. Children given the drug experienced on average 0.73 fewer vomiting episodes. Failure of oral rehydration therapy fell dramatically, with a risk ratio of 0.39, and the use of intravenous fluids dropped to 0.57 times the rate seen with placebo. Perhaps most tellingly for frontline practice, children who received ondansetron tolerated significantly more oral rehydration solution, a mean difference of nearly 48 milliliters more than placebo recipients. For a therapy whose entire purpose is to keep fluids going in by mouth rather than through a needle, that volume difference is clinically meaningful.

The picture darkens somewhat around the outcomes that matter most for health systems and families over longer horizons. The analysis found no significant difference between ondansetron and placebo in hospitalization rates, repeat healthcare visits, ongoing diarrhea, diarrheal episodes, or adverse events. Moreover, the hospitalization result proved fragile: it reached statistical significance only when a single large trial was omitted from the pooling, a sensitivity finding that undermines confidence in any true effect on admissions. Reassuringly for safety, the drug did not appear to worsen diarrhea, a concern sometimes raised because intestinal motility is partly serotonin-mediated. But the authors emphasize that the safety comparison rests on very few estimable comparisons and very few adverse events, meaning the analysis simply cannot rule out uncommon or delayed harms.

The durability of the antiemetic effect emerged as another key nuance. On subgroup analysis by follow-up duration, the benefit for ongoing vomiting was statistically significant through the first twenty-four hours but attenuated at forty-eight hours and beyond. This time-limited effect provides what the authors call a plausible rationale, though not direct evidence from the synthesis itself, for the extended multidose post-discharge regimen evaluated in the largest included trial. That trial, which the 2020 meta-analysis could not include, tested whether continued ondansetron after children left the emergency department could sustain the protection that a single dose evidently cannot. The updated evidence base now incorporates those findings, strengthening the argument that duration of action is a central design question rather than an afterthought.

Beneath the pooled estimates lies a more uncomfortable statistical story. The trials showed substantial heterogeneity, meaning their results varied far more than chance alone would predict. Exploratory meta-regression, introduced during revision and notably not specified in the registered protocol, suggested that the baseline proportion of male participants, baseline vomiting-episode frequency, and baseline diarrheal-episode frequency acted as study-level moderators of the effect on ongoing vomiting, while mean age did not. More concerning, Egger’s test indicated statistically significant funnel-plot asymmetry for both outcomes where publication bias could be assessed: ongoing vomiting, with a p-value of 0.03070, and number of vomiting episodes, with a p-value of 0.04627. Begg and Mazumdar’s rank correlation test was significant for neither, leaving the signal equivocal but sufficient for the authors to rate certainty of evidence as low for ongoing vomiting and very low for the number of vomiting episodes.

What does funnel-plot asymmetry mean in practical terms? Small trials with favorable results tend to be published more readily than small trials with null findings, so when the smaller studies in a meta-analysis cluster at one extreme of the funnel plot, it suggests the literature may be missing negative results. If so, the pooled effect sizes that look so impressive in the forest plots may overstate what a typical child would experience. The authors state this directly: the pooled magnitude of benefit on vomiting may be overstated. This kind of self-critical transparency is increasingly expected of high-quality systematic reviews, and it distinguishes this update from simpler aggregations that report point estimates without interrogating the shape of the evidence behind them.

The research team, which also included authors from Hawassa University in Ethiopia and Ad Diriyah Hospital in Riyadh, concludes that ondansetron significantly reduces vomiting morbidity in children with acute gastroenteritis, with no statistically significant difference versus placebo in adverse events or diarrhea. Their prescription for future research is precise: further randomized trials directly comparing single-dose and multidose regimens, particularly in high-burden, low-resource settings where gastroenteritis still kills, along with individual patient-data analyses that can resolve the heterogeneity that study-level meta-regression only glimpses. The review was registered prospectively on PROSPERO under identifier CRD420261447906, received no extramural funding, and is published open access. For emergency clinicians deciding whether a dose of ondansetron is worth offering a vomiting, dehydrated child, the accumulated evidence now points, with acknowledged caveats, toward yes.

Subject of Research: Efficacy and safety of ondansetron versus placebo for acute gastroenteritis-associated vomiting in children

Article Title: Updated evidence on efficacy and safety of ondansetron compared with placebo for acute gastroenteritis-associated vomiting in children: a systematic review and meta-analysis of randomized controlled trials

Article References: Althunayyan, B. S., Alhoushani, R. A., Alhesayani, L. M., Alsallal, S. A., Aldakhil, L. N., Alharbi, S. J., Alharbi, M. M., Aldaher, Y. J., Aljumah, Y. S., Alharbi, W. A., Yusuf, S. A., & Alrashidi, S. H. (2026). Updated evidence on efficacy and safety of ondansetron compared with placebo for acute gastroenteritis-associated vomiting in children: a systematic review and meta-analysis of randomized controlled trials. BMC Pediatrics. https://doi.org/10.1186/s12887-026-07694-6

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07694-6

Keywords: ondansetron, acute gastroenteritis, vomiting, children, oral rehydration therapy, meta-analysis, randomized controlled trials, pediatrics, emergency care, intravenous fluids, publication bias, GRADE