Side effects of anti sickness medicines

Side effects are unwanted or unpleasant effects of a treatment. Different medicines have different side effects. Some are very rare and only a few people will have them. By law, drug companies must list every side effect that has been reported to them, no matter how rare they are.

Your doctor or nurse should tell you about the most likely side effects of any drugs before you take them. And you can ask your doctor or nurse for more information if you are worried.

Let your doctor or nurse know as soon as possible if you have any side effects. Your doctor can usually give you other medicines to help.

Serotonin blockers (such as ondansetron)

These medicines block receptors in the gut and brain that send messages to the chemoreceptor trigger zone and the vomiting centre in the brain. They are also called 5HT3 blockers.

You might have serotonin blockers such as ondansetron or granisetron for cancer treatment related nausea and vomiting.

The most common side effects include:

  • headaches
  • constipation

Drinking plenty of fluids, eating a high fibre diet and taking exercise can all help with constipation. You might need other medicines (laxatives) to help if your constipation continues.

When you take serotonin blockers for chemotherapy sickness, you have them for a short period only. This means they are less likely to cause constipation.

Steroids (such as dexamethasone)

Steroids can help particularly with sickness from increased pressure in your brain or a blockage in your gut. They are also used as anti sickness medicines for chemotherapy with other anti sickness medicines.

The side effects depend on:

  • the type of steroid you have
  • the dose
  • how long you take it for

The most common steroid given for sickness from chemotherapy is dexamethasone. You usually have it before chemotherapy and for a few days afterwards.

Side effects of dexamethasone include:

  • trouble sleeping - taking your steroids before lunchtime can help
  • mood changes
  • flushing or tingling when dexamethasone is injected - this is rare
  • pain, itching or tingling in the vagina in women or between the legs (perineum) in men when it's injected quickly - this is not serious and usually lasts less than a minute
  • indigestion
  • fungal infection (thrush)

Antihistamines and sedatives

These types of medicines include:

  • cyclizine
  • lorazepam
  • haloperidol

You might feel drowsy when you are taking these medicines.

Metoclopramide and prochlorperazine

Metoclopramide works by blocking the vomiting centre in your brain. It also acts directly on the wall of the gut. It encourages the stomach to empty its contents into your bowel. Prochlorperazine also acts by blocking the vomiting centre in the brain.

These medicines can cause twitching in your arms, legs or face. This is rare but more likely in children and young adults.

Stop taking the medicine and let your doctor or nurse know if you notice this side effect.


Domperidone speeds up the emptying of your stomach. It also acts on a part of your brain called the chemoreceptor trigger zone. A common side effect is a dry mouth. Although rare, domperidone can cause uncontrolled movements or twitching.

This side effect is more likely to happen in children.

Let your doctor or nurse know if you get this side effect.


Aprepitant is a newer medicine which works by blocking a substance in the body called neurokinin. Fosaprepitant is a similar drug which can be given by injection into the bloodstream. Some of the common side effects of aprepitant and fosaprepitant include:

  • constipation
  • indigestion
  • headache
  • tiredness (fatigue)


Olanzapine blocks a number of receptors in the gut and brain. Doctors think this is why it's helpful for sickness in people having chemotherapy.

The main side effects include:

  • drowsiness
  • feeling dizzy (especially when getting up from a sitting or lying position)

More information about anti sickness drugs

For further information about each anti sickness medicine and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflets on this website.

  • Electronic Medicines Compendium

    Accessed November 2023

  • The Royal Marsden Manual of Clinical and Cancer Nursing Procedures (10th edition, online)
    S Lister, J Hofland and H Grafton 
    Wiley Blackwell, 2020

  • Olanzapine for the Prevention and Treatment of Chemotherapy-Induced Nausea and Vomiting: A Review to Identify the Best Way to Administer the Drug

    X-L Zhang and J-E Ying

    Current Oncology, 2022. Volume 29, Issue 11

Last reviewed: 
09 Nov 2023
Next review due: 
09 Nov 2026

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