Aprepitant: what it treats, how to take it, side effects
Last updated September 3, 2026.
Aprepitant (brand name Emend) is a prescription medicine that prevents nausea and vomiting caused by chemotherapy. It blocks NK1 receptors in the brain's vomiting center and is given together with other anti-nausea drugs, not on its own.
What does it treat?
Aprepitant prevents both the immediate and the delayed nausea and vomiting that follow highly or moderately emetogenic cancer chemotherapy, including the cisplatin-based regimens notorious for days of delayed sickness. It is used in adults and in children 6 months and older. It prevents nausea; it is not a treatment for nausea that has already started.
How do you take it?
For adults, the standard schedule is 125 mg by mouth on day 1, then 80 mg on days 2 and 3, taken 1 hour before chemotherapy each day. If no chemo is given on days 2 and 3, take the capsule in the morning instead. Aprepitant is one part of a regimen that also includes dexamethasone and a 5-HT3 blocker such as ondansetron, so take the full set your oncology team prescribes. If you miss a dose, take it as soon as you remember unless the next dose is near; never take two doses together. Capsules can be taken with or without food.
Side effects to know
- Common: fatigue, diarrhea, weakness, indigestion, abdominal pain, hiccups, decreased appetite, headache, and low white blood cell counts; each occurred in at least 3% of adults in trials.
- Serious: allergic reactions including hives, rash, and trouble breathing, and serious skin reactions, which have been reported after the first dose and on repeat exposure.
Who should not take it?
Do not take aprepitant with pimozide or if you have had an allergic reaction to it. It interacts with many drugs through the CYP3A4 pathway, so your oncology team needs your full medication list. On warfarin, it can lower INR, so clotting tests are watched in the 2 weeks after each course, especially days 7 to 10. Hormonal contraceptives may work less well during aprepitant treatment and for 28 days after the last dose, so a backup or alternative method is recommended for that window. Safety in pregnancy has not been established.
When is it an emergency?
Call 911 for swelling of the face, lips, or throat, trouble breathing, or a widespread rash or peeling skin after a dose. Severe dizziness with fainting also warrants emergency care. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Does aprepitant treat nausea that has already started?
No. Aprepitant is a preventive medicine. It is taken before chemotherapy to stop nausea and vomiting from starting, including the delayed wave that can hit days after treatment. Once nausea is underway, other medicines are used for breakthrough symptoms.
Why do I take aprepitant for three days if chemo is only one day?
Chemotherapy nausea comes in two waves: an acute phase in the first 24 hours and a delayed phase that can run for several days. The day 2 and day 3 doses of 80 mg exist to cover the delayed phase, even on days when you receive no chemo.
Can aprepitant affect my birth control?
Yes, and this is easy to miss. The label warns that hormonal contraceptives may work less well during aprepitant treatment and for 28 days after the last dose, so use a backup or alternative method during that window.
Does aprepitant interact with warfarin?
Yes. Taking it with warfarin can cause a clinically meaningful drop in INR, the number that tracks your blood thinning. The label directs INR monitoring in the 2 weeks after starting each aprepitant course, particularly at 7 to 10 days.
Can I take aprepitant with food?
Yes. The capsule can be taken with or without food. The timing that matters is the 1 hour before chemotherapy, not the meal.
Is aprepitant a steroid?
No. It is an NK1 receptor antagonist, a different class entirely. It is, however, usually prescribed alongside a steroid (dexamethasone) and a 5-HT3 blocker such as ondansetron, and the three drugs work on different parts of the vomiting reflex.