Drug interactions
Anastrozole + Ethinylestradiol
Severity: Major
Anastrozole and Ethinylestradiol: major interaction.
Last updated Sources: US FDA label
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Anastrozole works by lowering estrogen levels in postmenopausal women with hormone-receptor-positive breast cancer. Estrogen-containing products such as ethinylestradiol supply the hormone it is meant to deprive, so they can reduce or cancel its benefit.
What this interaction means in plain words
Anastrozole and Ethinylestradiol can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
Pharmacodynamic antagonism: exogenous estrogen counteracts aromatase inhibitor-induced estrogen suppression.
What to do
Avoid estrogen-containing products during anastrozole therapy. Use non-hormonal options for contraception or menopausal symptoms.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Anastrozole
- Anastrozole + Bazedoxifene / conjugated estrogens Contraindicated
- Anastrozole + Bazedoxifene-conjugated estrogens Contraindicated
- Anastrozole + Conjugated estrogens Contraindicated
- Anastrozole + Estradiol Contraindicated
- Anastrozole + Estrogens conjugated synthetic Contraindicated
- Anastrozole + Estrogens esterified Contraindicated
Frequently asked questions
Can I take Anastrozole with Ethinylestradiol?
MediHelp rates the interaction as major. Anastrozole and Ethinylestradiol can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Anastrozole works by lowering estrogen levels in postmenopausal women with hormone-receptor-positive breast cancer. Estrogen-containing products such as ethinylestradiol supply the hormone it is meant to deprive, so they can reduce or cancel its benefit.
How serious is the interaction between Anastrozole and Ethinylestradiol?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid estrogen-containing products during anastrozole therapy. Use non-hormonal options for contraception or menopausal symptoms.
What other medicines interact with Anastrozole?
MediHelp also lists interactions of Anastrozole with, for example, Bazedoxifene / conjugated estrogens, Bazedoxifene-conjugated estrogens, Conjugated estrogens. The full list is on the Anastrozole page.
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