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Antiemetic Drugs

Introduction

Nausea and vomiting are common symptoms with various potential causes, such as morning sickness during early pregnancy, motion sickness, gastroenteritis, and adverse reactions of chemotherapy and anaesthesia. Antiemetics are medicines used to treat or prevent nausea and vomiting, including those associated with cancer therapy, anaesthesia, and motion sickness.


Multiple physiological pathways can trigger nausea and vomiting, hence, different classes of antiemetic drugs target distinct mechanisms to relieve these symptoms. In general, activation of the chemoreceptor trigger zone (CTZ) and the vomiting centre in the brain induces nausea and vomiting. Antiemetics work by inhibiting specific neurotransmitter receptors in these areas.

Types of Antiemetic Drugs

There are several classes of antiemetics. Commonly used examples include:

  • Antihistamines e.g. promethazine, dimenhydrinate
  • Anticholinergics e.g. hyoscine
  • Dopamine antagonists e.g. metoclopramide, domperidone, and phenothiazines – prochlorperazine, chlorpromazine
  • 5-HT3 receptor antagonists e.g. ondansetron, granisetron, palonosetron
  • Neurokinin-1 receptor antagonists e.g. aprepitant, fosaprepitant, netupitant

The choice of antiemetics depends on the underlying cause. For example, hyoscine or antihistamines such as dimenhydrinate are commonly used for motion sickness. In contrast, 5-HT3 receptor antagonists and neurokinin-1 receptor antagonists are typically used to manage postoperative or chemotherapy-induced vomiting.

Side Effects of Commonly Used Antiemetics*

  1. Antihistamines: drowsiness, headache, dry mouth, dry nasal passages, blurred vision, constipation, urinary difficulty or retention.
  2. Anticholinergics: dry mouth, drowsiness, blurred vision, constipation, dizziness, dyspepsia, flushing, headache, palpitations, skin reactions, tachycardia, urinary disorders.

    3. Other possible side effects associated with hyoscine patch:

    • Difficulty in urinating;
    • Impairment of memory or concentration, restlessness, disorientation, confusion, or hallucinations;
    • Increase in body temperature due to decreased sweating.

  3. Dopamine antagonists (including phenothiazines): sedation, dizziness, headache, abnormal face and body movements, tremor, restlessness, hyperprolactinaemia.
  4. 5-HT3 receptor antagonists: headache, constipation, flushing, local injection site reactions.
  5. Neurokinin-1 receptor antagonists: headache, dizziness, appetite decreased, gastrointestinal discomfort, constipation, dyspepsia, fatigue, increases in alanine aminotransferase (ALT) or aspartate aminotransferase (AST) levels, hiccups.

General Advice*

  • Antiemetics offer temporary symptomatic relief and do not treat the underlying cause of nausea and vomiting. Use only as directed by your doctor or pharmacist. Prolonged use should be avoided.
  • Antiemetics may mask symptoms and delay the diagnosis of serious diseases, therefore, medical consultation is recommended before use.
  • Always follow the dosage and administration instructions prescribed by your doctor.
  • Consult your doctor if symptoms persist or worsen.
  • Consult your doctor before taking any medications, and avoid self-medication during pregnancy or breastfeeding without medical advice.
  • Extra caution is advised when administering antiemetics to children or the elderly due to increased sensitivity to adverse effect.
  • Repeated vomiting following a head injury requires immediate medical attention.
  • Seek urgent medical consultation if vomit contains blood or appears green.
  • Do not take other medicines or health supplements unless they have been discussed with your doctor.
  • Avoid driving or operating machinery after taking antiemetics, as many of these drugs may cause drowsiness and impair coordination.
  • Do not consume alcohol while taking antiemetics, as it can enhance the sedative effects of these medications.

Storage

Antiemetics should be stored in a cool dry place. Refrigeration is not generally required unless specified on the drug labels. Always keep medications out of reach and sight of children to prevent accidental ingestion.

* Information contained herein may not cover all possible side effects, precautions, drug interactions, allergic reactions, or adverse effects.



Drug Office
Department of Health
October 2025
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