Tamoxifen: Uses, Dosage & Side Effects

Tamoxifen is a selective estrogen receptor modulator that acts as an estrogen antagonist in breast tissue while having agonist effects in bone and cardiovascular tissue. It remains a gold standard for hormone receptor-positive breast cancer.

• Adjuvant treatment of node-negative and node-positive breast cancer
• Metastatic breast cancer in postmenopausal women
• Breast cancer risk reduction in high-risk women (BRCA mutations, strong family history)
• Ductal carcinoma in situ (DCIS)
• Prevention of contralateral breast cancer

Standard Dosing:

• 20 mg once daily or 10 mg twice daily
• Take with or without food
• Treatment duration typically 5 years; may extend to 10 years in selected cases

Adjuvant Therapy:

• Initiated after surgery, radiation, and/or chemotherapy
• Continuous daily dosing for entire treatment period

Common: Hot flashes, vaginal discharge/bleeding, nausea, weight gain, mood changes Serious: Endometrial cancer (2-3 fold increased risk), thromboembolic events (DVT/PE), stroke, cataracts, retinal deposits

• Pregnancy or concurrent use in women of childbearing potential (highly teratogenic)
• Active thromboembolism
• Undiagnosed vaginal bleeding
• History of thromboembolic events (relative contraindication; requires careful risk assessment)
• Concurrent warfarin therapy (relative)

• CYP2D6 inhibitors (paroxetine, fluoxetine, bupropion): reduce tamoxifen efficacy by decreasing active metabolite (endoxifen) formation
• Warfarin: increased anticoagulant effect; monitor INR closely
• Aromatase inhibitors: sequential or concurrent use in some protocols
• Megestrol acetate: additive effects for advanced disease

NSABP B-24 trial (JNCI 2004) demonstrated tamoxifen reduces recurrence and mortality in early breast cancer. IBIS-I trial demonstrated 38% risk reduction for contralateral breast cancer in high-risk women. Emergence of aromatase inhibitors has shifted treatment paradigms for postmenopausal women.

• Baseline assessment before initiating therapy
• Regular clinical follow-up per indication
• Laboratory parameters as specified in sections above
• Drug interaction screening at each visit

Dosing adjustments may be necessary in:

• Renal impairment
• Hepatic impairment
• Elderly patients
• Pregnancy and lactation
• Pediatric patients

• Take exactly as directed; do not modify dose without consulting healthcare provider
• Report any unusual symptoms or adverse effects
• Maintain regular follow-up appointments
• Store at room temperature away from moisture and light
• Keep out of reach of children

Disclaimer: This information is for educational purposes only and should not substitute for professional medical advice. Always consult with a qualified healthcare provider before starting, stopping, or modifying any medication.