Antiemetics

General management

There are several underlying conditions which precipitate nausea and vomiting, which also affects treatment choice.

Gastric stasis 

Drugs which have a prokinetic effect can be used for nausea and vomiting induced by gastric stasis (unlicensed in the UK). Most commonly, dopamine antagonists metoclopramide and domperidone are used. The antibiotic erythromycin also has prokinetic activity. 

Prokinetics (metoclopramide and domperidone) should not be given concurrently with drugs with antimuscarinic activity (e.g., cyclizine, hyoscine) because antimuscarinic drugs competitively block the action of prokinetics.

Motion sickness/Labyrinth disorders/Vertigo

Antihistamines such as cyclizine, cinnarizine, prochlorperazine and hyoscine butylbromide are most commonly used 

Palliative care

Several classes of antiemetics can be used in palliative care, the class used may depend on whether there is a known precipitating factor causing the nausea and vomiting i.e. chemotherapy or gastric stasis, and the route of administration available. Commonly used antiemetics in palliative care include haloperidol, levomepromazine, cyclizine and dexamethasone. 

Chemotherapy-induced nausea 

5HT3 receptor antagonists such as ondansetron and granisetron, aprepitant and dexamethasone are often used for chemotherapy induced nausea and vomiting 

Nausea and vomiting during pregnancy

Antiemetics should be considered for persistent symptoms where self-care measures are not effective. Few drugs are licensed in pregnancy in the UK, however use is based on established practice. However, xonvea is licensed for use in the UK for nausea and vomiting during pregnancy. Xonvea comprises of doxylamine succinate (a first generation antihistamine) and pyridoxine hydrochloride (vitamin B6), both of which contribute to the antiemetic effect.

Common antiemetics used in pregnancy include: chlorpromazine hydrochloride, cyclizine, metoclopramide, prochlorperazine, promethazine hydrochloride, promethazine teoclate, and ondansetron. 

Postoperative nausea and vomiting (PONV)

Drugs commonly used in PONV include 5HT3 receptor antagonists, dexamethasone, cyclizine and prochlorperazine. 

By TeachMeSeries Ltd (2026)

Fig 2: Apfel score

Antiemetic classes

Dopamine receptor antagonists

Dopamine receptor antagonists, such as metoclopramide and domperidone, block dopamine type 2 (D2) receptors centrally in the chemoreceptor trigger zone and peripherally in the gastrointestinal tract. Domperidone and metoclopramide also stimulate gastric emptying as described above.

Metoclopramide crosses the blood-brain barrier (domperidone does not), therefore is not recommended in Parkinson’s disease where there is a lack of dopamine in the brain. Metoclopramide can also induce acute dystonic reactions which are more likely in younger or elderly patients and females. 

Domperidone should be used with caution in patients with a cardiovascular history, as it can cause QT interval prolongation, and there is an increased association with ventricular tachyarrhythmias and sudden cardiac death, which is more likely to be seen at higher doses (>30mg daily) and in older patients (>60yrs).

First-generation antipsychotics such as levomepromazine, chlorpromazine, haloperidol and prochlorperazine are also D2 receptor antagonists and can have an antiemetic effect. Alongside being cautioned in use with patients with Parkinson’s disease, and risk of QT prolongation, these drugs have additional side effects such as weight gain, hyperprolactinaemia, hyperglycaemia and urinary retention due to activity at additional receptors such as α -adrenoceptors. 

Antihistamines

Antihistamines such as cyclizine, cinnarizine and promethazine are often used in nausea and vomiting related to motion sickness/labyrinth disorders/vertigo. Antihistamines block H1 receptors, as well as muscarinic receptors*. Promethazine also blocks D2 receptors. 

Blocking muscarinic receptors leads to anticholinergic side effects such as dry mouth, urinary retention, movement disorders, blurred vision, drowsiness, constipation and arrhythmias. Promethazine can also cause QT prolongation. 

Caution should be taken with IV cyclizine which can cause a euphoric effect when administered. Furthermore, if cyclizine is used in a syringe driver; it should not be mixed with 0.9% NaCl as this can cause precipitation. 

*Cinarrizine, cyclizine, promethazine all block muscarinic receptors. 

5HT3-receptor antagonists

Serotonin receptor antagonists such as ondansetron and granisetron block 5-HT3 receptors in the vagal nerve terminals in the GI tract, in the CTZ and the vomiting centre in the brainstem. 

Both can cause QT prolongation, constipation, movement disorders and granisetron can also cause serotonin syndrome. Both are commonly used in chemotherapy- or radiotherapy-induced nausea and vomiting, as serotonin is the main neurotransmitter responsible for emesis after chemo or radiotherapy. 

Neurokinin antagonists

Neurokinin antagonists such as aprepitant block neurokinin type 1 receptors in the central and peripheral nervous system. 

Aprepitant has several clinically significant drug interactions being a substrate, moderate inhibitor (during treatment) and an inducer (after the end of treatment) of the enzyme CYP3A4 and a mild inducer of CYP2C9.

Caution should be taken with concomitant administration of aprepitant with medications also metabolised by CYP3A4 which have a narrow range (e.g. ciclosporin, tacrolimus) and CYP2C9 (e.g. warfarin). 

Furthermore, the efficacy of hormonal contraceptives may be reduced during and for 28 days after administration of aprepitant, as hormonal contraceptives are metabolised by CYP3A4. Alternative backup methods should be used during treatment and for 2 months after the last dose.

Muscarinic antagonists

Muscarinic antagonists, such as hyoscine hydrobromide, block acetylcholine binding to muscarinic receptors in vestibular nuclei, vomiting centre and higher brain centres. 

Muscarinic antagonists are a subtype of anticholinergic drugs that specifically block muscarinic receptors, therefore also lead to anticholinergic side effects such as drowsiness, blurred vision, arrhythmias, dry mouth and constipation.

Summary table

The table below describes commonly used antiemetics by class, mechanism of action, common side effects, cautions and contraindications. 

References

1. NICE CKS Palliative care – nausea and vomiting: Prescribing a prokinetic. Last revised in March 2022. Available from: Prescribing a prokinetic | Prescribing information | Palliative care – nausea and vomiting | CKS | NICE. accessed 15/8/24.
2. Metoclopramide hydrochloride | Drugs | BNF | NICE accessed 19/8/24
3. Athavale A, Athavale T, Roberts DM. Antiemetic drugs: what to prescribe and when. Aust Prescr. 2020 Apr;43(2):49-56. doi: 10.18773/austprescr.2020.011. Epub 2020 Apr 1. PMID: 32346211; PMCID: PMC7186277. 
4. BNF: Nausea and labyrinth disorders. Available from: Nausea and labyrinth disorders | Treatment summaries | BNF | NICE. Accessed 15/8/24
5. BNF Domperidone, available from: Domperidone | Drugs | BNF | NICE accessed 15/8/24
6. BNF Haloperidol, available from https://bnf.nice.org.uk/drugs/haloperidol/ accessed 18/8/24
7. BNF Chlorpromzine available from https://bnf.nice.org.uk/drugs/chlorpromazine-hydrochloride/ accessed 18/8/24
8. BNF Prochlorperazine available from: Prochlorperazine | Drugs | BNF | NICE accessed 18/8/24
9. Levomepromazine | Drugs | BNF | NICE accessed 19/8/24
10. Cinnarizine | Drugs | BNF | NICE accessed 19/8/24
11. Medicinal forms | Promethazine hydrochloride | Drugs | BNF | NICE accessed 18/8/24
12. Promethazine teoclate | Drugs | BNF | NICE accessed 18/8/24
13. Cyclizine | Drugs | BNF | NICE accessed 18/8/24
14. Ondansetron | Drugs | BNF | NICE accessed 18/8/24
15. Granisetron | Drugs | BNF | NICE accessed 18/8/24
16. Aprepitant | Drugs | BNF | NICE accessed 20/8/24
17. Hyoscine hydrobromide | Drugs | BNF | NICE accessed 20/8/24
18. Xonvea 10 mg/10 mg gastro-resistant tablets – Summary of Product Characteristics (SmPC) – (emc) | 14892 accessed 14/12/25