tamoxifen vs warfarin
Side-by-side comparison of tamoxifen and warfarin. Data from FDA drug databases (Orange Book, NDC Directory, recalls, shortages) covering 20,000+ approved drugs, plus CMS pricing; see our methodology.
major Known Drug Interaction
( 7.1 ) Warfarin: Do not use in patients taking tamoxifen for DCIS and for reduction in breast cancer incidence in women at high risk. Warfarin A marked increase in anticoagulant effect may occur when tamoxifen is used in combination with warfarin. Closely monitor coagulation indices in patients who are taking tamoxifen for either the treatment of metastatic breast cancer or as adjuvant therapy who require concomitant use of warfarin [see Contraindications (4) ] .
Recommendation: Avoid using these together if you are taking tamoxifen for cancer prevention, or have your doctor check your blood clotting levels very often.
Tamoxifen (Soltamox) is a medicine that can treat breast cancer. It can also lower the chance of getting breast cancer in some people.
Warfarin is a medicine that helps prevent blood clots. It is used to treat and prevent dangerous clots from forming in your body.
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.
Warfarin is used to prevent and treat blood clots in your veins and lungs. It can also prevent clots if you have atrial fibrillation (irregular heartbeat) or a replacement heart valve. After a heart attack, it can lower the risk of death, another heart attack, or a stroke.
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.
Warfarin works by blocking your body's use of vitamin K. Vitamin K is needed to make blood clotting factors. By blocking vitamin K, warfarin makes your blood less likely to clot.
- • Hot flashes
- • Mood changes
- • Vaginal discharge
- • Vaginal bleeding
- • Nausea
- • Bleeding from any tissue or organ
- Tiredness 391
- Feeling sick to your stomach 337
- Loose stools 274
- Joint pain 271
- Cancer getting worse 249
- INR increased 10,275
- Shortness of breath 8,408
- Interaction with another medicine 6,289
- Tiredness 6,141
- Feeling sick to your stomach 5,921
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.
Warfarin can cause major or fatal bleeding. You must have your blood tested regularly (INR) while taking warfarin. Many things, like other medicines and diet changes, can affect your INR. Tell your doctor about any bleeding and follow their instructions to prevent bleeding.
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.
Warfarin can harm your unborn baby, especially during the first three months of pregnancy. Do not take warfarin if you are pregnant, unless you have a mechanical heart valve and your doctor says the benefits outweigh the risks. Talk to your doctor if you are breastfeeding, and watch your baby for bruising or bleeding.
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How to Read This tamoxifen vs warfarin Comparison
tamoxifen is classified in the Selective Estrogen Receptor Modulator (SERM) drug class, while warfarin sits within the Vitamin K Antagonist (Anticoagulant) 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, tamoxifen has 1,522 submissions while warfarin has 37,034. 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 major interaction flagged in FDA labeling, attributed to tamoxifen increases the blood-thinning effects of warfarin, which can lead to a much higher risk of dangerous bleeding.. 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 tamoxifen and warfarin - 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.