Tamoxifen Citrate Tablets

(Commercial Product)

Available Dosage Strengths

2 mg

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Product Overview

Description

Tamoxifen, an oral selective estrogen receptor modulator (SERM) approved in the 1970s, has both estrogenic and antiestrogenic effects in the body. The drug is a competitor inhibitor of estrogen at the estrogen receptor in breast tissue. By inhibiting estrogen activity at the breast tissue estrogen receptor, it can decrease the growth of estrogen dependent breast tumors.

In females, tamoxifen is used for 1) the adjuvant treatment of breast cancer and for the treatment of metastatic breast cancer, 2) to reduce the risk of invasive breast cancer in women with ductal carcinoma in situ (DCIS) after surgery and radiation, and 3) to reduce the risk of breast cancer in women at high risk for breast cancer. ^1,2

In males, tamoxifen’s activity as a SERM is used to increase testosterone in comparison to estrogen in hypogonadism to facilitate testosterone production in the testes.³

Mechanism of Action

In females, tamoxifen decreases estrogen binding to estrogen-dependent breast tissue. This activity of tamoxifen decreases the growth of estrogen-dependent breast tumors and on a molecular level, the inhibition of the expression of estrogen-dependent genes (RNA transcription). Tamoxifen’s activity results in reduced DNA polymerase activity, impaired thymidine utilization, blockade of estradiol uptake, and decreased estrogen response. Tamoxifen’s activity is cytostatic and occurs in the G2 phase. Tamoxifen also inhibits other factors involved in cancer growth, including insulin-like growth factor type 1 (IGF-1) and transforming growth factor-beta (TGF-beta).^1,2 In males, tamoxifen works as an estrogen antagonist in the hypothalamus and pituitary gland to inhibit negative feedback from estrogen. This negative feedback allows for release of LH and FSH which results in the production of testosterone and spermatogenesis.³

Adverse Reactions

Common^1,2

Gastrointestinal-nausea, abdominal cramps, anorexia
Reproductive system-amenorrhea, altered menses, oligomenorrhea, ovarian cyst
Other-fatigue, hair loss, hot flashes

Contraindications & Precautions

Contraindications^1,2

Known hypersensitivity to tamoxifen or any component of the formulation
Tamoxifen is contraindicated during pregnancy.

Precautions^1,2

Increased risk of thromboembolic events and stroke
Risk of endometrial cancer, endometrial hyperplasia, uterine sarcoma
Increased cholesterol and lipoproteins. Lipid levels should be monitored in patients with preexisting dyslipidemia.
Increased risk of cataracts, retinopathy, and corneal changes. Use caution in patients with visual impairment or cataract history.

Storage

Store tamoxifen tablets at controlled room temperature, between 68°F to 77°F (20°C to 25°C).¹

Protect the medication from excessive heat, moisture, and direct light.¹

Keep all medications out of the reach of children.¹

References

Tamoxifen package insert. https://www.accessdata.fda.gov/drugsatfda_docs/label/2005/17970s053lbl.pdf. August 27, 2004. Accessed June 27, 2025
Clinical Pharmacology tamoxifen clinical monograph 2025 https://www.clinicalkey.com/pharmacology/
Rambhatla A, Mills JN, Rajfer J. The Role of Estrogen Modulators in Male Hypogonadism and Infertility. Rev Urol. 2016;18(2):66-72.

Disclaimer

This sheet is a summary. It may not cover all possible drug information about this product. Call your doctor for medical advice and/or about side effects. You may report side effects to the FDA at 1-800-FDA-1088. A Wells Pharmacy Network pharmacist will be happy to answer any questions. For consultation, please call 1-800-622-4510.