Treatment and the treatment process

Anti-sickness medicines

Chemotherapy can cause nausea and vomiting. Modern anti-sickness (antiemetic) medicines usually prevent this reliably.

Last updated: 14 October 2026~2 min read

On a dark navy background, red ripples over a stomach shape calm into teal and gold light. — **Figure 1.**Treatment calms the wave of nausea.

01Short answer

Nausea and vomiting are among the most feared side effects of chemotherapy, but today they can be prevented in most cases. Every protocol has an "emetogenic risk" — the chance it will cause sickness: high, moderate, low or minimal. Based on that risk, the doctor combines several medicines: serotonin (5-HT3) blockers (ondansetron, granisetron, palonosetron), NK1 blockers (aprepitant, fosaprepitant), dexamethasone and sometimes olanzapine. Acute nausea happens in the first day after chemotherapy and delayed nausea in the following days; "anticipatory" nausea can start before treatment because of past experience. The protocol and the doctor set the doses and schedule.

02Simple explanation

The signal. Chemotherapy sends a signal from the gut and blood to the brain’s "vomiting centre".

Blocking it. Medicines close off that signal’s path.

Timing. They work best taken before nausea begins.

Extra help. Small meals, fresh air and rest also help.

03Scientific explanation

Mechanism: cytotoxic drugs make enterochromaffin cells in the gut lining release serotonin, which activates 5-HT3 receptors on the vagus nerve and the trigger zone in the brainstem. In the delayed phase, substance P and NK1 receptors play the main role.

Risk-based prevention: under MASCC/ESMO, ASCO and NCCN guidance, highly emetogenic regimens combine a 5-HT3 blocker, an NK1 blocker, dexamethasone and often olanzapine, with fewer components at moderate risk. In multi-day regimens (such as leukemia induction), prevention is repeated each day.

Safety: 5-HT3 blockers can cause constipation, headache and QT prolongation; aprepitant interacts with some drugs via CYP3A4; metoclopramide can cause extrapyramidal symptoms and olanzapine drowsiness. Dexamethasone raises blood sugar.

04What happens in the body?

Why does nausea happen?

Chemotherapy irritates the inner lining of the gut, which sends a "poison" signal to the brain. The vomiting centre responds with vomiting — an ancient protective reflex.

How do the medicines work?

Each drug group closes a different "gate" on the signal’s path. That is why a combination protects better than a single medicine.

A nerve signal from the gut to the brain is stopped by small golden shields at receptor gates. — **Figure 2.**Antiemetics block the path of the nausea signal.

How can you help yourself?

Note when nausea happens and how strong it is, eat small amounts and keep drinking. These notes help the doctor tailor your treatment.

A notebook, a pen and a cup of warm ginger tea on a bedside table in morning light. — **Figure 3.**A nausea diary helps fine-tune treatment.

05A plan against nausea

A simplified outline.

1Risk assessedThe protocol’s emetogenic risk.

2PreventionMedicines before chemotherapy.

3Following daysTaken on schedule.

4When neededA "rescue" medicine and a call.

Preventing nauseaPossible in most cases.

A personal planIf it doesn’t work, the medicine is changed.

On timeBefore nausea starts.

06Main antiemetic groups

Group	Examples	Note
5-HT3 blockers	Ondansetron, granisetron, palonosetron	Acute nausea; may cause constipation
NK1 blockers	Aprepitant, fosaprepitant	Delayed nausea; interactions
Corticosteroids	Dexamethasone	Boosts other drugs; raises sugar
Atypical antipsychotic	Olanzapine	High risk; drowsiness
Dopamine blockers	Metoclopramide, prochlorperazine	"Rescue" medicine
Benzodiazepines	Lorazepam	Anticipatory nausea, anxiety

* The protocol and your doctor choose the combination, doses and duration.

07Key terms

Antiemetic: A medicine against nausea and vomiting.
Emetogenic risk: How likely a treatment is to cause sickness.
Acute nausea: Nausea in the first day after chemotherapy.
Delayed nausea: Nausea in the following days.
Anticipatory nausea: Nausea before treatment, triggered by past experience.
"Rescue" medicine: An extra medicine taken if nausea starts.

08Key points

Nausea can usually be prevented.
Medicines are taken on schedule, before nausea.
A combination protects better.
Delayed nausea is treated too.
If it isn’t working, tell your team — the plan will change.
If vomiting lasts more than a day, call straight away.

09Frequently asked questions

Can I skip a dose if I don’t feel sick?

No — unless your doctor says otherwise, keep to the schedule: the medicines work better when taken in advance.

I vomited my tablet — what should I do?

Call your team; they will decide on a repeat dose or another form (injection, suppository).

Does ginger help?

Some people find it pleasant, but it does not replace medicines; discuss any extras with your doctor.

Why am I constipated?

Medicines such as ondansetron can cause constipation; tell your team and they will help.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

Can I skip a dose if I don’t feel sick?
I vomited my tablet — what should I do?
Does ginger help?
Why am I constipated?

My questions

12Sources

National Cancer Institute (NCI). Chemotherapy to Treat Cancer
Cancer Research UK. Chemotherapy
National Cancer Institute (NCI). Nausea and Vomiting and Cancer Treatment
Macmillan Cancer Support. Nausea and vomiting
Cancer Research UK. Cancer and sickness (nausea)
MedlinePlus. Ondansetron
Cancer Research UK. Blood test
MedlinePlus. Bone Marrow Transplantation
National Marrow Donor Program (NMDP). Finding a donor
NHS. How a stem cell or bone marrow transplant is done

Medical disclaimerThis information is for educational purposes only and does not replace medical advice.

Last updated: 14 October 2026← Back to the list

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