Abemaciclib: what it treats, how to take it, side effects
Last updated September 6, 2026.
**Abemaciclib (Verzenio) is a targeted breast cancer medicine called a CDK4/6 inhibitor.** It blocks proteins that help cancer cells divide. Severe diarrhea can cause dehydration and infection, so start your prescribed diarrhea treatment, drink fluids, and contact your oncology team at the first loose stool.
What does it treat?
You may receive abemaciclib for hormone receptor-positive, HER2-negative breast cancer. For early cancer involving lymph nodes with a high recurrence risk, it accompanies tamoxifen or an aromatase inhibitor. For advanced or metastatic cancer, it accompanies an aromatase inhibitor initially, fulvestrant after hormone therapy stops working, or is used alone after prior hormone therapy and chemotherapy for metastatic disease.
How do you take it?
Tablets come in 50, 100, 150, and 200 mg strengths. The usual adult dose is 150 mg twice daily with hormone therapy, totaling 300 mg daily, or 200 mg twice daily alone, totaling the highest recommended daily dose of 400 mg. Your prescribed limit may be lower. Swallow intact tablets whole at consistent times, with or without food; avoid grapefruit. Skip missed or vomited doses without doubling. Stop and call your oncology team if diarrhea does not improve within 24 hours despite treatment.
Side effects to know
- Common: You may develop diarrhea, nausea, vomiting, abdominal pain, fatigue, reduced appetite, hair thinning, infections, or low blood cell counts.
- Serious: Hold further doses and get immediate medical advice for fever, severe diarrhea, yellow skin or eyes, unusual bleeding, new cough, or a painful swollen limb. Breathing trouble or chest pain needs emergency evaluation for lung inflammation or a blood clot.
Who should not take it?
Discuss allergies, infection, blood clots, lung problems, and liver or kidney disease before treatment. Review all medicines and supplements for interactions. Abemaciclib can harm a fetus: obtain a pregnancy test before starting if you can become pregnant, and use effective contraception during treatment and for 3 weeks afterward. Do not breastfeed during treatment or for 3 weeks afterward. The label sets no alcohol limit; discuss drinking with your oncology team.
When is it an emergency?
For overdose, call Poison Control at 1-800-222-1222 immediately, even without symptoms. Severe diarrhea, vomiting, or dehydration requires urgent assessment. Call 911 for collapse, breathing trouble, chest pain, or face or throat swelling suggesting anaphylaxis. Fever or chills, very little urine, or a newly swollen painful leg needs immediate medical evaluation.
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Common questions
What is the maximum dose?
The highest recommended dose is 200 mg twice daily when used alone. With hormone therapy, the usual dose is 150 mg twice daily. Never exceed your prescription; severe liver impairment requires once-daily dosing.
Can I drink alcohol?
The FDA label does not specify a safe alcohol amount. Ask your oncology team before drinking. Avoid alcohol while you have diarrhea, vomiting, or dehydration.
Can I take it during pregnancy?
Abemaciclib can harm your fetus. Use effective contraception during treatment and for 3 weeks after your last dose. Contact your oncology team immediately if you become pregnant.
Should I take it with food?
You can take it with or without food. Avoid grapefruit and grapefruit juice. Swallow tablets whole without splitting, crushing, or chewing.
What are overdose signs?
There is no specific symptom pattern that reliably identifies overdose. Diarrhea or vomiting can occur during treatment, but do not wait for symptoms after an extra dose. Call Poison Control at 1-800-222-1222; call 911 for collapse or breathing trouble.
Which medicines interact with it?
Ketoconazole should be avoided, and clarithromycin can require an abemaciclib dose reduction. Rifampin and St. John's wort can reduce its effect. Have your oncology pharmacist check every medicine and supplement before you start or stop it.