Pharmacology · Class
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
Drugs in this class
- MetoclopramideA D2 blocker that stops nausea and speeds up the stomach. Long or heavy use can cause tardive dyskinesia, a movement…Dopamine D2 receptor
- ProchlorperazineA phenothiazine that blocks dopamine in the vomiting centre. It controls severe nausea but can cause dystonia, low…Dopamine D2 receptor
- DomperidoneA D2 blocker that relieves nausea and speeds the stomach while barely entering the brain. Its risk is the heart: QT…Dopamine D2 receptor
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).
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 (DailyMed (U.S. National Library of Medicine), 2026); Nausea and Vomiting - Gastroenterology - MSD Manual Professional Edition (MSD Manual Professional Edition, 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.