Tamoxifen

Competitive estrogen receptor antagonist in breast tissue — blocks estrogen stimulation of breast cell proliferation. Agonist in bone — preserves bone density. In the hypothalamus, estrogen receptor blockade removes negative feedback on LH and FSH release — stimulating gonadotropin secretion and endogenous testosterone production. This is the basis of its use in post-cycle recovery.

Non-steroidal oral compound. No ester. Long half-life of 5-7 days. Active metabolite endoxifen has a half-life of 12-14 days — contributing to the extended active period.

Tamoxifen is used in performance settings primarily in post-cycle therapy protocols to stimulate the recovery of natural testosterone production after HPTA suppression from anabolic use. By blocking estrogen receptors in the hypothalamus, it removes the negative feedback that estrogen exerts on GnRH pulsatility, leading to increased LH and FSH secretion and subsequent endogenous testosterone stimulation. It is also used during cycles to manage gynecomastia by blocking estrogen receptors in breast tissue, though it does not reduce circulating estrogen levels the way an aromatase inhibitor does.

Tamoxifen is not stacked with performance compounds in the traditional sense. It is used in the PCT phase after the cycle has ended. It is commonly combined with Clomid in PCT protocols because the two SERMs work through overlapping but not identical mechanisms and the combination is believed to provide more robust LH and FSH stimulation than either alone. HCG is typically used in the transition period before Tamoxifen and Clomid are started, with HCG discontinued before the SERMs begin to avoid the interaction between direct gonadotropin stimulation and upstream receptor modulation.

• Estrogen receptor-positive breast cancer — standard of care
• Breast cancer prevention in high-risk women
• Gynecomastia treatment
• Male infertility — hypogonadotropic hypogonadism
• McCune-Albright syndrome

• Hot flashes — most common
• Thromboembolic events — DVT, pulmonary embolism risk
• Endometrial cancer risk — uterine agonism with chronic use
• Vision disturbances — corneal changes, cataracts (rare)
• Mood changes — depression reported
• Partial agonist effects can cause some estrogen-like side effects
• Vaginal dryness and sexual dysfunction

The thromboembolic risk associated with Tamoxifen, documented in clinical use for breast cancer, is relevant in performance settings where individuals are often already in a prothrombotic state due to elevated hematocrit from anabolic use. The combination of elevated red blood cell mass and a compound that increases clotting risk creates a meaningful DVT and pulmonary embolism exposure. The partial agonist properties of Tamoxifen mean it has estrogenic effects in some tissues, which can complicate estrogen management during PCT when estrogen levels are already in flux.

WADA detection via urinary tamoxifen and metabolites. Weeks detection window.