Ondansetron
| Evidence Level: L2 | Predicted Indications: 10 |
Table of Contents
Ondansetron: From Nausea and Vomiting Control to Tourette Syndrome
One-Sentence Summary
Ondansetron is a 5-HT3 receptor antagonist, widely marketed in Singapore as an antiemetic. The approved indication text was not available in the data compiled for this report. The TxGNN model predicts it may be effective for Tourette syndrome, the highest-ranked prediction that has real supporting evidence. This direction is supported by 1 completed clinical trial and 11 publications, including 2 randomized controlled trials.
Note: The #1 TxGNN prediction (nephrogenic syndrome of inappropriate antidiuresis) has no trials or literature and no plausible mechanism. This report therefore focuses on Tourette syndrome (rank 2), the best-supported candidate.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Not stated in the licence data; ondansetron is known as an antiemetic (nausea and vomiting) |
| Predicted New Indication | Tourette syndrome (rank 2; rank 1 was nephrogenic syndrome of inappropriate antidiuresis, with no supporting evidence) |
| TxGNN Prediction Score | 97.96% |
| Evidence Level | L2 |
| Singapore Market Status | ✓ Marketed |
| Number of Registrations | 16 |
| Recommended Decision | Proceed with Guardrails (research question stage) |
Why is This Prediction Reasonable?
Detailed mechanism-of-action data was not available in the data compiled for this report. Ondansetron is a selective 5-HT3 receptor antagonist. Its efficacy against chemotherapy-induced and post-operative nausea and vomiting is well established.
5-HT3 receptors modulate dopamine transmission in the mesolimbic and striatal circuits implicated in tic generation. By blocking these receptors, ondansetron may dampen dopaminergic hyperactivity. This is the proposed link between an antiemetic and a tic disorder.
Clinical findings are consistent with this idea. A 1999 open-label pilot study, a 2005 randomized placebo-controlled trial, a 2025 RCT of high-dose ondansetron and a case report all examined it in Tourette syndrome or related conditions. One genetic study (2005) found no involvement of the HTR3A/HTR3B genes in Tourette syndrome. This weakly argues against a direct genetic basis, though it does not rule out a pharmacological effect.
Clinical Trial Evidence
| Trial Number | Phase | Status | Enrollment | Key Findings |
|---|---|---|---|---|
| NCT03239210 | Phase 4 | Completed | 110 | 4 weeks of ondansetron 24 mg/day vs placebo on symptoms and brain function (MRI) in OCD and tic disorders; results not available in the compiled data |
Literature Evidence
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 39876680 | 2025 | RCT | American Journal of Psychiatry | High-dose ondansetron vs placebo for 4 weeks on sensory phenomena severity and brain connectivity in OCD and tic disorders |
| 15816793 | 2005 | RCT | J Clin Psychiatry | 3-week randomized, double-blind, placebo-controlled study of ondansetron in Tourette's disorder |
| 40489853 | 2025 | Review | Medicine | Narrative review of Phase III and IV pharmacological trials in Tourette syndrome |
| 21183132 | 2010 | Review | Semin Pediatr Neurol | Summary of RCTs of drugs for tics and stereotypies in children |
| 11474424 | 2001 | Review | CNS Drug Reviews | Ondansetron as a 5-HT3 antagonist and its uses in CNS-related disorders |
| 10565805 | 1999 | Open-label pilot | Int Clin Psychopharmacol | Six haloperidol-resistant men with Tourette's syndrome treated with ondansetron; assessed with tic and OCD scales |
| 18184945 | 2008 | Case report | J Child Neurol | A boy with leukaemia and Tourette syndrome; tics eased on ondansetron and returned when the dose was reduced |
| 16314763 | 2005 | Genetic study | Psychiatr Genet | HTR3A and HTR3B variants not involved in Tourette syndrome |
| 21568361 | 2011 | Review | Drugs | Common features of OCD, impulse control disorders and addiction, and potential treatments |
Singapore Market Information
All 16 registrations are single-ingredient products and currently valid. The approved indication text was not available in the data compiled for this report. Five main authorizations are listed below.
| Authorization Number | Product Name | Dosage Form | Approved Indication |
|---|---|---|---|
| SIN05133P | ZOFRAN TABLET 8 mg | Film-coated tablet | Not available |
| SIN05135P | ZOFRAN INJECTION 2 mg/ml | Injection | Not available |
| SIN15558P | ONRON 8 Solution for Injection or Infusion 2 mg/ml | Injectable solution | Not available |
| SIN15742P | Ondansetron B. Braun Solution for Injection or Infusion 2 mg/ml | Injectable solution | Not available |
| SIN15004P | ONDAVELL Film-Coated Tablet 8 mg | Film-coated tablet | Not available |
Both oral (tablet, film-coated tablet) and injectable forms are registered.
Safety Considerations
- Disease-level cautions (from the knowledge graph, not label text): Ondansetron has contraindication links to long QT syndrome, familial long QT syndrome, torsades de pointes, liver failure, epilepsy, basal ganglia disease, focal hand dystonia and blepharospasm. Cardiac QT risk is especially important at the high doses (24 mg/day) used in the tic trials.
- Drug Interactions: 100 interactions were found. Examples rated Major:
- Serotonergic agents: tramadol, sumatriptan, almotriptan, dextromethorphan
- Opioids: fentanyl, alfentanil
- QT-prolonging agents: amiodarone, amisulpride, amitriptyline, anagrelide
Examples rated Moderate: codeine, dihydrocodeine, famotidine, formoterol, salbutamol, adenosine, alfuzosin, celecoxib, abiraterone and abametapir.
Please refer to the package insert for label warnings and contraindications.
Conclusion and Next Steps
Decision: Proceed with Guardrails
Rationale: Tourette syndrome is the only predicted indication with meaningful evidence. It has a completed Phase 4 trial (n=110), a 2025 RCT and a 2005 placebo-controlled RCT. However, the available RCTs appear small or exploratory, no Phase 3 trial is documented, and the Phase 4 results are not in the compiled data. It is therefore graded L2 and treated as a research question rather than a ready-to-adopt use. The other nine predictions (including the top-ranked nephrogenic SIAD) are model predictions only (L5) and should be on Hold.
To proceed, the following is needed:
- Retrieve and review the results of NCT03239210 and the 2025 RCT (PMID 39876680) for efficacy and safety
- Obtain the full text of the 2005 RCT for effect size and sample size
- Complete the mechanism-of-action data (DrugBank)
- Download and parse the HSA package inserts for warnings, contraindications and approved indications
- Perform a QT-risk assessment and a drug-interaction plan for the high-dose regimen
- Confirm that the oral route is available for the required dosing (oral tablets are registered in Singapore)
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.