letrozole vs tamoxifen
Side-by-side comparison of letrozole and tamoxifen. Data from FDA drug databases (Orange Book, NDC Directory, recalls, shortages) covering 20,000+ approved drugs, plus CMS pricing; see our methodology.
moderate Known Drug Interaction
7 DRUG INTERACTIONS Anastrozole and letrozole: Should not be used in combination with tamoxifen. Letrozole The concomitant use of letrozole with tamoxifen is not recommended because the efficacy of the combination in the adjuvant treatment of breast cancer has not been established. Tamoxifen reduced the plasma concentration of letrozole by 38% when these drugs were co-administered [see Clinical Pharmacology (12.3) ].
Recommendation: You should avoid using these two medications at the same time.
Letrozole is a medicine that lowers estrogen levels in women after menopause. It is used to treat breast cancer that is affected by hormones.
Tamoxifen (Soltamox) is a medicine that can treat breast cancer. It can also lower the chance of getting breast cancer in some people.
Letrozole is used to treat breast cancer in women who have gone through menopause. It can be used as an initial treatment, after other treatments like tamoxifen, or when the cancer has spread. It works best for cancers that are hormone receptor positive or when the hormone receptor status is unknown.
This medicine is used to treat breast cancer that has spread in adults. It can also be used after surgery to help prevent breast cancer from returning in adults. Tamoxifen can also lower the risk of invasive breast cancer after breast surgery and radiation for ductal carcinoma in situ (DCIS). Finally, it can lower the chance of getting breast cancer in women who are at high risk.
Letrozole blocks a protein called aromatase in the body. Aromatase makes estrogen. By blocking aromatase, letrozole lowers the amount of estrogen, which can slow or stop the growth of breast cancer cells that need estrogen to grow.
Tamoxifen belongs to a class of drugs called Selective Estrogen Receptor Modulators (SERMs). It works by blocking the effects of estrogen in breast tissue. This can help to stop the growth of breast cancer cells.
- • Hot flashes
- • Joint pain
- • Flushing
- • Weakness
- • Swelling
- • Hot flashes
- • Mood changes
- • Vaginal discharge
- • Vaginal bleeding
- • Nausea
- Tiredness 7,158
- Feeling sick to your stomach 5,259
- Low white blood cell count 4,896
- Loose stools 4,460
- Cancer getting worse 4,253
- Tiredness 391
- Feeling sick to your stomach 337
- Loose stools 274
- Joint pain 271
- Cancer getting worse 249
Letrozole can cause bone thinning, which may lead to fractures. Your doctor may monitor your bone density. Letrozole can also harm an unborn baby, so you must not take it if you are pregnant. Use effective birth control if you could become pregnant.
Tamoxifen can cause serious and life-threatening problems, including cancer of the uterus, stroke, and blood clots in the lungs. Some cases have been fatal. Talk to your doctor about the risks and benefits of taking tamoxifen, especially if you are at high risk for breast cancer or have DCIS. For most people already diagnosed with breast cancer, the benefits of tamoxifen outweigh the risks.
Do not take letrozole if you are pregnant because it can harm your unborn baby. If there is any chance you could become pregnant, use birth control while taking letrozole. Do not breastfeed while taking letrozole.
Tamoxifen can harm an unborn baby. If you are a woman who could become pregnant, your doctor will perform a pregnancy test before you start taking tamoxifen. Use effective birth control while taking tamoxifen and for several months after your last dose. Do not breastfeed while taking this medicine.
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How to Read This letrozole vs tamoxifen Comparison
letrozole is classified in the Aromatase Inhibitor drug class, while tamoxifen sits within the Selective Estrogen Receptor Modulator (SERM) class. Drugs from different classes work through distinct mechanisms, so a head-to-head comparison illustrates trade-offs rather than equivalence. Both drugs are prescription-only, so a licensed provider must authorize use.
Adverse event totals above are pulled from the FDA's Adverse Event Reporting System (FAERS). For these top-ranked reactions alone, letrozole has 26,026 submissions while tamoxifen has 1,522. Those figures reflect cumulative reporting volume, not per-patient risk, so older, widely dispensed drugs typically look worse on count alone. These two drugs have a known moderate interaction flagged in FDA labeling, attributed to tamoxifen lowers the amount of letrozole in your blood, and it is not known if taking both together helps treat cancer effectively.. Serious warnings, pregnancy guidance, and contraindications can differ even when indications overlap.
A table cannot substitute for clinical judgment. Effectiveness, tolerability, drug-drug interactions with your other medications, kidney and liver function, pregnancy status, insurance formulary, and price all feed into a decision that only a licensed prescriber can make responsibly. Data here is sourced from FDA Structured Product Labels (SPL) and FAERS, both of which update as manufacturers and clinicians submit new information. This page is for educational purposes only, is not medical advice, and should not be used to self-switch between letrozole and tamoxifen - always consult your physician or pharmacist first.
Important: This comparison is for informational purposes only. Drug effects vary between individuals. Always consult your doctor or pharmacist for personalized medical advice.