Key points
- Nausea and vomiting are among the commonest side effects of chemotherapy and radiotherapy, but anti-sickness medicines given before treatment prevent or reduce them in most patients [1].
- Preventing sickness is much easier than treating it once it has started; that is why the guidelines recommend using the most effective combination of medicines from the very first cycle [1, 8].
- The anti-sickness medicine is chosen according to how likely the chemotherapy drug is to cause sickness; for drugs that very often cause sickness, a combination of four medicines including olanzapine is recommended [3].
- Sickness can happen in the first 24 hours (acute), from day two to day seven (delayed) or even before a treatment session (anticipatory); take your medicines exactly on schedule, even if you feel well [1].
- Small, frequent meals, plain and cold foods, avoiding strong smells and sipping fluids help reduce sickness [1].
- If you cannot keep down fluids or your medicines, or you have signs of dehydration (dizziness, severe weakness, confusion), call your care team straight away [1].
Why does cancer treatment cause sickness?
Some chemotherapy drugs cause the release of chemicals such as serotonin from gut cells and substance P in the brain. These chemicals attach to receptors in the gut and in the vomiting centre of the brain and trigger nausea and vomiting. The newer anti-sickness medicines block exactly these receptors [6].
Nausea and vomiting can happen at different times [1]:
- Acute: in the first 24 hours after treatment starts.
- Delayed: from day one to day seven after treatment.
- Anticipatory: before a treatment session; when someone has had sickness in earlier cycles and a smell, sound or the sight of the treatment area sets it off again.
Besides chemotherapy, radiotherapy (especially to the brain, upper abdomen or whole body), some targeted drugs and immunotherapy, painkillers, anxiety, constipation and the illness itself (for example cancers of the abdomen or brain) can also cause sickness [1].
| Group | Without anti-sickness medicine | Examples |
|---|---|---|
| High | Almost all patients vomit | Cisplatin; the combination of cyclophosphamide and doxorubicin (AC) in breast cancer [3] |
| Moderate | 3 to 9 in every 10 patients | Carboplatin, oxaliplatin and many other treatments [4] |
| Low | 1 to 3 in every 10 patients | Many targeted drugs and some chemotherapy [2] |
| Very low | Fewer than one in 10 | Immunotherapy on its own [2] |
Based on the guidelines of international cancer societies [2, 7]. Your doctor chooses the anti-sickness medicine according to your drugs and your situation (for example younger age, being a woman, a history of morning sickness in pregnancy or travel sickness).
What helps?
A practical plan for treatment days
- 1
Take your medicines on schedule
Anti-sickness medicines are usually given before chemotherapy and then for a few days afterwards. Take them on time even if you do not feel sick; the aim is prevention [1]. If you have also been given an "as needed" medicine, take it at the first sign of nausea.
- 2
Small, frequent meals
Instead of three big meals, eat five or six small meals a day. Plain, starchy foods (toast, rice, plain pasta, plain biscuits or crackers) and cold foods (yoghurt, jelly, ice lollies) are usually better tolerated. Avoid fatty, fried, very sweet or spicy foods [1].
- 3
Keep away from strong smells
The smell of coffee, fish, onion, garlic, perfume or scented candles can make sickness worse. Eat in a well-ventilated room, and if cooking smells bother you, ask others to prepare the food [1].
- 4
Sip fluids
Sip water, clear broth, fruit juice, tea or drinks containing ginger little by little through the day so you do not become dehydrated. If you are losing weight, choose drinks with calories over plain water [1].
- 5
Rest after eating
After a meal, rest sitting up or with your head raised for about 30 minutes, and do not lie down straight away [1].
- 6
Relaxation and acupressure
Deep breathing, guided imagery, music and meditation help reduce sickness. Pressing a point on the wrist or wearing acupressure wristbands may also help alongside medicines; check with your doctor before trying them [1].
- 7
Keep a sickness diary
Write down when the sickness started, how long it lasted and what you ate or did beforehand. This helps your doctor adjust the medicines for the next cycle [1].
Always talk to your doctor before taking any supplement or herbal remedy for sickness; some of them may reduce the effect of anticancer drugs [1].
What can your doctor do?
Show detailsHide
The main groups of anti-sickness medicines
Ondansetron and similar medicines
Aprepitant
Dexamethasone (a steroid)
Together with other medicines, it strengthens the anti-sickness effect; even when immunotherapy is given with chemotherapy, it does not need to be left out [2].
Olanzapine
Adding it to the usual medicines nearly doubled the number of patients with no nausea at all in the 5 days after strong chemotherapy; its main side effect is drowsiness [5].
For physicians
Guideline summary for physicians
- Highly emetogenic chemotherapy (HEC): the 2023 MASCC/ESMO update makes olanzapine a fixed part of the four-drug regimen (NK1 antagonist + 5-HT3 antagonist + dexamethasone + olanzapine) in both non-AC HEC and AC. After AC regimens, dexamethasone is not needed beyond day 1, but in non-AC HEC a 4-day dexamethasone regimen is recommended. No major differences were seen between drugs in the same class (5-HT3 or NK1) [3].
- Moderately emetogenic chemotherapy (MEC): a 5-HT3 antagonist with a steroid is standard; for carboplatin AUC ≥5 and for women under 50 on oxaliplatin-based regimens, a three-drug combination with an NK1 antagonist is recommended. In MEC, limit the steroid to day 1. Sacituzumab govitecan and trastuzumab deruxtecan have shown emetogenicity similar to carboplatin AUC above 5 [4].
- ASCO 2020: a 5 mg olanzapine dose in adults was added as an option; immune checkpoint inhibitors alone or as a combination of two immunotherapies do not need routine antiemetic prophylaxis [2].
- From the first cycle, use the most effective regimen for the risk and do not wait to assess the response to a weaker regimen; olanzapine is also an option for breakthrough nausea and vomiting [8].
Myths and facts
| Common belief | Fact |
|---|---|
| Chemotherapy always means severe vomiting. | With today's anti-sickness regimens most patients do not have severe vomiting; prevention medicines given before treatment work well in most people [1]. |
| When I feel well, I do not need to take my anti-sickness medicine. | Delayed sickness can happen up to 7 days after treatment, and preventing it is easier than treating it; keep taking your medicines on schedule [1]. |
| Taking anti-sickness medicine is a sign that the treatment is not working. | Anti-sickness medicines are a standard part of treatment and do not harm the effect of chemotherapy; even with immunotherapy, leaving out dexamethasone is not recommended [2]. |
| Sickness with immunotherapy is the same as with chemotherapy. | Checkpoint inhibitors on their own usually cause little sickness and do not need routine prevention; new sickness in these patients should be checked [2]. |
When should I call my doctor?
Call your care team straight away or go to the emergency department if:
- You cannot keep down fluids or tablets (including anti-sickness medicines).
- You have signs of dehydration: dizziness, severe weakness, confusion, a dry mouth or passing very little, dark urine [1].
- You have a temperature of 38 °C or higher during chemotherapy; this may be a sign of serious infection and is an emergency [9].
- Sickness goes on despite taking your medicines regularly or stops you eating and drinking; your doctor can change the medicines [1].
Frequently asked questions
Is it normal to feel sick before a chemotherapy session (even at the sight of the hospital)?
Does ginger really work?
Drinks and foods containing ginger may settle nausea a little and can be used alongside medicines [1]; but they do not replace prescribed anti-sickness medicines. Talk to your doctor before taking ginger supplements (capsules or extracts).
Olanzapine is a psychiatric medicine; why has it been prescribed for me?
Olanzapine controls sickness well by blocking several receptors in the brain, and international guidelines recommend it for chemotherapy that very often causes sickness [3, 5]. Being prescribed it does not mean you have a mental illness. The commonest side effect is drowsiness [5]; do not drive until you know how it affects you.
If I vomit after taking an anti-sickness tablet, should I take another?
Ask your care team beforehand what to do in this situation [1]. Some anti-sickness medicines also come as tablets that dissolve under the tongue, suppositories or injections, which your doctor can prescribe if needed.
References
9 referencesShow all references, 7 with a study cardClose the reference list
Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
- 1
- 2
- 3
- 42023 updated MASCC/ESMO Consensus recommendations: Prevention of nausea and vomiting following moderately emetic risk antineoplastic agents
- 5
- 6Antiemetic Prophylaxis for Chemotherapy-Induced Nausea and Vomiting
- 7
- 8Antiemetics: American Society of Clinical Oncology Clinical Practice Guideline Update
- 9Infection and Neutropenia during Cancer Treatment
This page is based on reputable scientific sources and was last updated on 28 October 2026. The content of this website is for educational and informational purposes only and does not replace consultation, diagnosis or treatment by a specialist physician. Consult your treating physician about any treatment decision.
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