Tamoxifen is a selective estrogen receptor modulator (SERM) from the triphenylethylene group. It acts as an estrogen antagonist in most tissues (breast, hypothalamus, pituitary) while exhibiting partial agonist activity in others, such as bone tissue, helping preserve bone density. Originally developed for breast cancer treatment, tamoxifen is widely used in post-cycle therapy (PCT) and hormonal recovery protocols due to its ability to stimulate natural testosterone production by modulating the hypothalamic–pituitary–gonadal (HPG) axis. Main Effects Stimulates endogenous testosterone production; Blocks estrogen receptors in key tissues; Prevents and helps reverse gynecomastia; Restores HPG axis function; Supports bone mineral density; Reduces risk of estrogen rebound after hormonal cycles Precautions Avoid combination with progestin-based compounds (e.g., nandrolone, trenbolone); Monitor liver function during prolonged use; Use cautiously in individuals with risk of thromboembolic events; Medical supervision is recommended Side Effects Hot flashes and sweating; Nausea, dizziness, fatigue; Mood swings or sleep disturbances; Rare visual disturbances; Possible elevation of liver enzymes with long-term use Contraindications Pregnancy and breastfeeding; Active or history of thromboembolic disorders; Severe liver disease; Concurrent progestin therapy; Hypersensitivity to tamoxifen Storage Store at 20–25 °C (68–77 °F); Keep in a dry, dark place; Protect from moisture and sunlight; Keep out of reach of children Mechanism of Action Tamoxifen competitively binds to estrogen receptors, blocking estrogen activity in target tissues. This reduces negative feedback on the hypothalamus and pituitary, increasing GnRH, LH, and FSH secretion, which stimulates endogenous testosterone production and supports hormonal recovery. Pharmacological Profile Half-life: approximately 5–7 days; Selective estrogen receptor modulation; Anti-estrogenic in breast tissue, partial agonist in bone; Supports lipid profile and bone health; Widely used in PCT and hormonal regulation protocols