Tamoxifen

Hormonal / PCT

Also known as: Nolvadex, Tamoxifen Citrate, TAM, ICI 46474

Selective Estrogen Receptor ModulatorsResearch phase: FDA-approvedRegulatory: FDA-approved for breast cancer treatment and prevention (1977). Available by prescription as Nolvadex and generics.

Mechanism

Tamoxifen is the original SERM, FDA-approved for breast cancer treatment and prevention since the 1970s. It blocks estrogen receptors in breast tissue while acting as a partial estrogen agonist in bone and uterus. In the peptide/performance community, it is widely used for post-cycle therapy (PCT) to restore natural testosterone production after anabolic suppression by stimulating pituitary LH and FSH release.

Technical detail

Tamoxifen is a first-generation non-steroidal SERM that competitively binds estrogen receptors (ER-alpha and ER-beta) with tissue-selective effects determined by differential coactivator/corepressor recruitment. In breast tissue, it functions as an ER antagonist, blocking estrogen-driven proliferation. In the hypothalamic-pituitary axis, it blocks estrogen negative feedback, increasing GnRH pulsatility and consequent LH/FSH secretion — the basis for PCT use. In bone and uterus, it acts as a partial ER agonist, maintaining bone density but carrying endometrial stimulation risk (including rare endometrial carcinoma).

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