levothyroxine vs tamoxifen
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Side-by-side comparison of levothyroxine and tamoxifen. Data from FDA drug databases (Orange Book, NDC Directory, recalls, shortages) covering 20,000+ approved drugs, plus CMS pricing; see our methodology.
minor Known Drug Interaction
Drugs That May Alter T4 and Triiodothyronine (T3) Serum Transport Without Affecting Free Thyroxine (FT4) Concentration (Euthyroidism) Drug or Drug Class Effect Clofibrate Estrogen-containing oral contraceptives Estrogens (oral) Heroin / Methadone 5-Fluorouracil Mitotane Tamoxifen These drugs may increase serum thyroxine-binding globulin (TBG) concentration. Drugs That May Alter T4 and Triiodothyronine (T3) Serum Transport Without Affecting Free Thyroxine (FT4) Concentration (Euthyroidism) Drug or Drug Class Effect Clofibrate Estrogen-containing oral contraceptives Estrogens (oral) Heroin /...
Synthroid, Levoxyl, Tirosint
Nolvadex
Levothyroxine is a medicine that replaces a hormone normally made by your thyroid gland. It is used when the thyroid doesn't make enough hormone on its own.
Tamoxifen (Soltamox) is a medicine that can treat breast cancer. It can also lower the chance of getting breast cancer in some people.
This medicine treats hypothyroidism, a condition where the thyroid gland doesn't make enough thyroid hormone. It can be used in adults and children, even newborns. Levothyroxine can also be used after surgery and radioiodine therapy for thyroid cancer to help lower thyroid-stimulating hormone (TSH) levels.
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.
Levothyroxine provides a synthetic form of thyroxine (T4), which is the main hormone produced by the thyroid gland. Your body converts T4 into triiodothyronine (T3), the active form of the hormone. By providing T4, levothyroxine helps restore normal thyroid hormone levels in your body.
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.
- • Fatigue
- • Increased appetite
- • Weight loss
- • Feeling hot
- • Headache
- • Hot flashes
- • Mood changes
- • Vaginal discharge
- • Vaginal bleeding
- • Nausea
- Fatigue 25,847
- Nausea 22,026
- Headache 18,797
- Diarrhoea 18,176
- Dyspnoea 16,216
- Tiredness 391
- Feeling sick to your stomach 337
- Loose stools 274
- Joint pain 271
- Cancer getting worse 249
Thyroid hormones, including levothyroxine, should not be used for weight loss or to treat obesity. Using high doses can cause serious and life-threatening side effects, especially when taken with stimulant medicines.
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.
Tell your doctor if you are pregnant or plan to become pregnant. Your levothyroxine dose may need to be adjusted during pregnancy. Levothyroxine passes into breast milk, but it is not expected to harm the baby.
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 levothyroxine vs tamoxifen Comparison
levothyroxine is classified in the Thyroid Hormone 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, levothyroxine has 101,062 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 minor interaction flagged in FDA labeling, attributed to tamoxifen increases the number of proteins that carry thyroid hormone in your blood, which can change your test results.. Serious warnings, pregnancy guidance, and contraindications can differ even when indications overlap.
A table cannot represent individual circumstances. Data here is sourced from FDA Structured Product Labels (SPL) and FAERS, both of which update as manufacturers and clinicians submit new information. This registry does not provide medical, treatment, substitution, or medication-change directions for levothyroxine or tamoxifen.
Registry boundary: This comparison displays source-record fields and does not provide individualized medical direction.