Class Explorer · Gastrointestinal
Antiemetics
Vomiting has several afferent routes, and each antiemetic class blocks one of them. Choosing by mechanism rather than by habit is what separates effective antiemesis from a sequence of failures.
Members
OndansetronExcellent for the vomiting it fits, useless for the vomiting it does not.MetoclopramideAn antiemetic that moves the stomach, and can lock up the neck.
Also in this class: Prochlorperazine · Dimenhydrinate · Aprepitant · Domperidone. Full pages arrive as the library grows.
Compare the members
Ondansetron
- Receptor
- 5-HT3
- Best for
- Chemotherapy, post-operative
- Watch
- QT, constipation
Metoclopramide
- Receptor
- D2, prokinetic
- Best for
- Gastric stasis, migraine
- Watch
- Extrapyramidal reactions
Shared across the class
- Indications
- Nausea and vomiting of varied cause
- Adverse effects
- Agent-specific · QT prolongation (ondansetron, droperidol) · Extrapyramidal effects (dopamine antagonists)
- Contraindications
- Bowel obstruction for prokinetics · Known QT prolongation for the 5-HT3 agents
- Monitoring
- Response, and a rethink at 24 hours rather than a fourth dose of a drug that is not working · ECG where QT risk factors stack · Movement effects with dopamine antagonists
What makes each agent different
- Ondansetron blocks 5-HT3 in the gut and chemoreceptor trigger zone: superb for chemotherapy and post-operative nausea, useless for vestibular causes, and constipating.
- Metoclopramide is a dopamine antagonist and a prokinetic: it suits gastroparesis and gastric stasis, and it causes extrapyramidal reactions, particularly in the young.
- Antihistamines and anticholinergics own the vestibular and motion causes that neither of the above touches.
Ask what is causing the vomiting before choosing the drug. Nausea from an opioid, from the vestibular system, from a bowel obstruction and from raised intracranial pressure need four different answers.
Metoclopramide in a young woman is the classic acute dystonia case seen in emergency departments.
Last reviewed 2026-08-16 · Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed.