Megestrol (Megace)

How does it work?

Megace tablets contain the active ingredient megestrol acetate, which is a synthetic form of the naturally occurring female sex hormone, progesterone. It is used to treat women with certain hormone-dependant cancers.

Most breast cancers and cancers affecting the womb (endometrial cancers) are sensitive to the female sex hormone oestrogen, and their growth is increased in the presence of this hormone. Oestrogen binds to oestrogen receptors on the cancer cells and causes changes within the cells that result in faster growth of the cancer.

Megestrol opposes the action of oestrogen, which means that the growth and replication of cancer cells is disrupted.

Megace tablets must usually be taken for at least two months to see if they are being effective.

What is it used for?

  • Breast cancer.
  • Endometrial cancer.


  • This medicine can cause abnormal blood clots in the blood vessels (for example deep vein thrombosis or pulmonary embolism), particularly during periods of immobilisation and following surgery. For this reason you should consult your doctor immediately if you experience any of the following symptoms during treatment: stabbing pains and/or unusual swelling in one leg, pain on breathing or coughing, coughing up blood, sudden breathlessness, sudden numbness affecting one side or part of the body, sudden or severe headache, fainting or sudden severe chest pain.
  • Women who could get pregnant should use an effective method of contraception to avoid pregnancy while taking this medicine, as it could be harmful to a developing baby.

Use with caution in

  • People with a history of inflammation of the veins associated with blood clots (thrombophlebitis).
  • Severely decreased liver function.
  • Hereditary blood disorders called porphyrias.

Not to be used in

  • Pregnancy.
  • Breastfeeding.
  • People with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption. (Megace tablets contain lactose)

This medicine should not be used if you are allergic to any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.

If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

  • This medicine should not be used during pregnancy as it may be harmful to the unborn baby. Seek medical advice from your doctor.
  • Women who could get pregnant should use an effective method of contraception to avoid pregnancy while taking this medicine, as it could be harmful to a developing baby.
  • This medicine may pass into breast milk. Mothers who need treatment with this medicine should not breastfeed. Seek medical advice from your doctor.

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

  • Increased appetite and weight gain.
  • Nausea and vomiting.
  • Swelling due to fluid retention.
  • Vaginal bleeding (breakthrough bleeding or spotting).
  • Difficulty breathing or shortness of breath (dyspnoea).
  • Heart failure.
  • High blood pressure.
  • Hot flushes.
  • Changes in mood.
  • High blood glucose level (hyperglycaemia).
  • Temporary stimulation of tumour growth (tumour flare).
  • Hair loss (alopecia).
  • Carpel tunnel syndrome.
  • Abnormal blood clots in the veins (thromboembolism – see warning section above).
  • Itchy rash (urticaria).

The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.

For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

There are no significant interactions reported with this medicine.

However, it is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to make sure that the combination is safe.

Other medicines containing the same active ingredient

There are currently no other medicines available in the UK that contain megestrol acetate as the active ingredient.