Last update March 30, 2023


Very High Risk

Very unsafe. Contraindicated. Use of an alternative or cessation of breastfeeding. Read the Comment.

Anastrozole is a selective aromatase inhibitor (estrogen synthetase), which inhibits the secretion of estrogen. Indicated in the treatment of breast cancer in postmenopause. Oral administration once a day for prolonged periods.

Since the last update we have not found published data on its excretion in breastmilk.

Its pharmacokinetic data (low molecular weight, low protein binding and prolonged half-life) enables transfer to breastmilk in amounts which could be significant.

During cancer treatment, breastfeeding must be interrupted due to potentially serious side effects for the infant.

Pharmacokinetics show that after 3 elimination half-lives (T½) 87.5% of the drug is eliminated from the body; after 4 T½ it is 94%, after 5 T½, 96.9%, after 6 T½, 98.4% and after 7 T½ it is 99%. From 7 T½ the plasma concentrations of the drug in the body are negligible. In general, a period of at least five half-lives can be considered a safe waiting period before breastfeeding again. (Anderson 2016)

According to this data, the interruption of breastfeeding would be for a period of between 10.4 days (5 T½) to 14.6 days (7 T½) after the administration of the last dose, which coincides with the estimates of other authors. (Hale)

Its long elimination half-life and its daily administration over many months make it impossible to continue breastfeeding.

Accidental intake of a single dose does not require an interruption of breastfeeding. However, treatment should not be continued. (Schaefer 2015)

See below the information of this related product:

  • Maternal Cancer ( Poorly safe. Evaluate carefully. Use safer alternative or interrupt breastfeeding 3 to 7 T ½ (elimination half-lives). Read the Comment.)


We do not have alternatives for أناستروزول.

Suggestions made at e-lactancia are done by APILAM team of health professionals, and are based on updated scientific publications. It is not intended to replace the relationship you have with your doctor but to compound it. The pharmaceutical industry contraindicates breastfeeding, mistakenly and without scientific reasons, in most of the drug data sheets.

Jose Maria Paricio, Founder & President of APILAM/e-Lactancia

Your contribution is essential for this service to continue to exist. We need the generosity of people like you who believe in the benefits of breastfeeding.

Thank you for helping to protect and promote breastfeeding.

José María Paricio, founder of e-lactancia.


أناستروزول belongs to this group or family:


Main tradenames from several countries containing أناستروزول in its composition:


Variable Value Unit
Oral Bioavail. 100 %
Molecular weight 293 daltons
Protein Binding 40 %
pKa 2.01 -
Tmax 2 hours
40 - 50 hours


  1. Hale TW. Medications & Mothers' Milk. 1991- . Springer Publishing Company. Available from Consulted on April 10, 2024 Full text (link to original source)
  2. Anderson PO. Cancer Chemotherapy. Breastfeed Med. 2016 May;11:164-5. Abstract Full text (link to original source) Full text (in our servers)
  3. AEMPS-Stada. Anastrozol. Ficha técnica. 2016 Full text (in our servers)
  4. Schaefer C, Peters P, Miller RK. Drugs During Pregnancy and Lactation. Treatment options and risk assessment. Elsevier, Third Edition. 2015
  5. Astra-Zeneca. Anastrozole. Data Sheet. 2010 Full text (in our servers)

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