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# Dopamine-antagonist antiemetics and prokinetics

Drugs that block dopamine D2 receptors in the vomiting centre and, some of them, speed up the stomach. Movement side effects are the price.

Updated 2026-11-01

## What they are

Metoclopramide, domperidone and the phenothiazine prochlorperazine block D2 receptors in the chemoreceptor trigger zone. Metoclopramide and domperidone are also prokinetics: they speed gastric emptying and are used in gastroparesis.

## Mechanism of action

The chemoreceptor trigger zone in the area postrema lies outside the blood–brain barrier and is rich in D2 receptors; dopamine there triggers nausea. Blocking D2 receptors at that site reduces vomiting. In the stomach, dopamine slows motility; D2 blockade removes that brake, so antral contractions grow, the pylorus relaxes and the stomach empties faster. Drugs that cross into the brain also block D2 receptors in the basal ganglia, which explains dystonia, parkinsonism, akathisia and tardive dyskinesia; domperidone barely crosses the blood–brain barrier.

Target: Dopamine D2 receptor

## Key points

- Metoclopramide carries a boxed warning for tardive dyskinesia: the risk rises with duration and total dose, and in diabetic gastroparesis treatment beyond 12 weeks is avoided.
- Acute dystonia is more frequent in children and young adults; metoclopramide is avoided in Parkinson disease and with other antipsychotics.
- Prokinetics are contraindicated when stimulating the gut could be dangerous: bleeding, mechanical obstruction or perforation.
- Any D2 blocker raises prolactin (galactorrhoea, amenorrhoea, gynaecomastia) and can cause neuroleptic malignant syndrome.
- Domperidone stays mostly outside the brain but can prolong QT and cause ventricular arrhythmias, so its use is restricted.

## Drugs in this class

- [**Metoclopramide** A D2 blocker that stops nausea and speeds up the stomach. Long or heavy use can cause tardive dyskinesia, a movement… Dopamine D2 receptor](https://durgical.com/en/pharmacology/metoclopramide/)
- [**Prochlorperazine** A phenothiazine that blocks dopamine in the vomiting centre. It controls severe nausea but can cause dystonia, low… Dopamine D2 receptor](https://durgical.com/en/pharmacology/prochlorperazine/)
- [**Domperidone** A D2 blocker that relieves nausea and speeds the stomach while barely entering the brain. Its risk is the heart: QT… Dopamine D2 receptor](https://durgical.com/en/pharmacology/domperidone/)

## Others in the class

- Droperidol
- Promethazine
- Haloperidol (off-label as an antiemetic)

## Test yourself

Think of the answer, then tap the question to see it.

## Why can a D2 antagonist act on the chemoreceptor trigger zone even if it barely enters the brain?

The trigger zone in the area postrema lies outside the blood–brain barrier, so drugs such as domperidone reach its D2 receptors.

## Which two actions make metoclopramide useful in diabetic gastroparesis?

It speeds gastric emptying (stronger antral contractions, relaxed pylorus) and it reduces nausea by blocking D2 receptors in the trigger zone.

## A young adult develops a sudden twisted neck and eye deviation after an IV antiemetic. Which class is the likely cause?

A dopamine D2 antagonist such as metoclopramide or prochlorperazine (acute dystonic reaction).

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - METOCLOPRAMIDE injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f6efdc63-a9df-4bbd-acf8-75fc9d1b0347) (DailyMed (U.S. National Library of Medicine), 2026); [Nausea and Vomiting - Gastroenterology - MSD Manual Professional Edition](https://www.msdmanuals.com/professional/gastrointestinal-disorders/symptoms-of-gastrointestinal-disorders/nausea-and-vomiting) (MSD Manual Professional Edition, 2025); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=A03FA) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/classes/dopamine-antagonist-antiemetics-and-prokinetics/