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Letrozole and Letrozole (Fertility) Interaction

Drug interaction information between Letrozole and Letrozole (Fertility).

Letrozole and Letrozole (Fertility) have a documented minor interaction in FDA labeling.

FDA drug labeling documents a minor-severity interaction between Letrozole and Letrozole (Fertility). Major interactions are generally avoided, moderate ones may need monitoring or a dose adjustment, and minor ones are usually low-risk. This page shows the documented mechanism and guidance. Label-documented interactions are not a complete safety review, so always confirm your own medications with a pharmacist or doctor. Educational information, not medical advice.

Drug A

Letrozole

Aromatase Inhibitor

Drug B

Letrozole (Fertility)

Aromatase Inhibitor (Off-Label Fertility)

How They Interact

Cimetidine does not have a meaningful effect on how letrozole is processed or used by the body.

What To Do

No special changes or dosage adjustments are needed when taking these two medications together.

FDA Label Information

7 DRUG INTERACTIONS Tamoxifen Coadministration of Femara and tamoxifen 20 mg daily resulted in a reduction of letrozole plasma levels of 38% on average (Study P015). Clinical experience in the second-line breast cancer trials (AR/BC2 and AR/BC3) indicates that the therapeutic effect of Femara therapy is not impaired if Femara is administered immediately after tamoxifen. Cimetidine A pharmacokinetic interaction study with cimetidine (Study P004) showed no clinically significant effect on letrozole pharmacokinetics.

Letrozole Also Interacts With

View all Letrozole interactions →

Letrozole (Fertility) Also Interacts With

View all Letrozole (Fertility) interactions →

Frequently Asked Questions

Can I take Letrozole and Letrozole (Fertility) together?

This is a minor interaction. No special changes or dosage adjustments are needed when taking these two medications together.

How serious is the interaction between Letrozole and Letrozole (Fertility)?

This interaction is classified as "minor" severity by the FDA. Minor interactions are unlikely to cause significant problems but should still be mentioned to your healthcare provider.

Why do Letrozole and Letrozole (Fertility) interact?

Cimetidine does not have a meaningful effect on how letrozole is processed or used by the body.

Understanding the Letrozole and Letrozole (Fertility) Interaction

FDA-approved prescribing information for these two drugs flags their combination as a minor-severity interaction. Letrozole belongs to the Aromatase Inhibitor class and Letrozole (Fertility) belongs to the Aromatase Inhibitor (Off-Label Fertility) class - two categories that can collide when co-prescribed. The mechanism described in FDA labeling is: Cimetidine does not have a meaningful effect on how letrozole is processed or used by the body. Severity tiers matter: major flags generally advise avoidance, moderate flags often require monitoring or dose adjustment, and minor flags may only call for awareness.

Context around a specific patient determines real-world impact. Letrozole has 4 total documented interactions on file in this dataset, and Letrozole (Fertility) has 4. Each additional medication compounds the interaction surface, which is why pharmacists run full-profile checks rather than evaluating one pair at a time. FDA-derived guidance for this pair is: No special changes or dosage adjustments are needed when taking these two medications together. Timing of doses, renal and hepatic function, age, and other concurrent prescriptions all shape whether a labeled interaction matters clinically.

An interaction flag is not a verdict. A large share of labeled interactions are managed routinely in clinical practice, the fix may be as simple as spacing doses or adding a monitoring test. Others require the prescriber to choose a different medication entirely. This page surfaces FDA-sourced labeling and openFDA data for educational purposes only; it is not medical advice and cannot account for your full clinical picture. Never start, stop, or adjust either Letrozole or Letrozole (Fertility) based on a web page, speak with your prescriber or pharmacist before making any change.

Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. Always consult your healthcare provider about drug interactions.