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How It Works

Megestrol is a man-made progestin similar to the hormone progesterone. Experts do not completely understand how megestrol works. But most believe that it interferes with receptors that help breast cancer grow and spread.

Why It Is Used

Megestrol can be used to treat metastatic or recurrent breast cancer after tamoxifen treatment. It can also be used when tamoxifen is not effective.

Megestrol is used mainly to treat breast cancer. It is also sometimes used to treat endometrial cancer and prostate cancer.

Megestrol can be used as an appetite stimulant for people experiencing loss of appetite and weight loss because of advanced cancer.

How Well It Works

Megestrol may be helpful for women with metastatic cancer who were already treated with another hormone therapy. But other medicines may work better than megestrol.

Megestrol may help relieve bone pain, and it can improve appetite and weight gain.1

Side Effects

Side effects of megestrol may include:

Megestrol may raise your risk for dangerous blood clots (deep vein thrombosis). This risk is even higher if you are a woman who smokes or if you have had blood clots in the past.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Megestrol should be used only under the supervision of a medical oncologist.

Megestrol can cause birth defects. Do not use this medicine if you are pregnant or wish to become pregnant.

If you have diabetes, you may need to adjust your insulin dose while you are being treated with megestrol. You will need regular appointments with your doctor to monitor your insulin levels.

Complete the new medication information form (PDF)Click here to view a form.(What is a PDF document?) to help you understand this medication.



  1. Stebbing J, Ngan S (2010). Breast cancer (metastatic), search date June 2009. Online version of BMJ Clinical Evidence:


ByHealthwise Staff
Primary Medical ReviewerSarah Marshall, MD - Family Medicine
Specialist Medical ReviewerDouglas A. Stewart, MD - Medical Oncology
Last RevisedAugust 11, 2011

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