Nolvadex (Tamoxifen)
Tamoxifen citrate, 1962 ICI Pharmaceuticals synthesis, FDA-approved (1977) for ER+ breast cancer. The AAS-PCT golden-standard SERM: pituitary ER-α blockade → LH/FSH disinhibition → endogenous testosterone recovery. 60+ years of clinical literature.
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Related comparisons
Nolvadex vs Clomid vs EnclomipheneWHAT IS NOLVADEX (TAMOXIFEN)?
Detailed overview
Nolvadex (tamoxifen citrate) is a non-steroidal triphenylethylene-class selective estrogen receptor modulator (SERM), synthesized in 1962 by Arthur Walpole and Dora Richardson at the ICI Pharmaceuticals (now AstraZeneca) Macclesfield laboratory. Original target: post-coital contraceptive – paradoxically turned out to be an ovulation inducer, and gained FDA approval in 1977 for estrogen-receptor-positive (ER+) breast cancer. To date 30+ million female and male patients have been treated with it, the longest-running SERM in clinical literature. In the AAS-PCT (post-cycle therapy) context, Nolvadex is the classic first-line choice: due to competitive antagonism of ER-α at the pituitary level, the hypothalamic-pituitary (HP) axis is released from negative feedback, LH and FSH secretion is restored, and Leydig cells restart endogenous testosterone production. Nolvadex's selectivity is tissue-specific: antagonist in breast tissue, agonist in bone, liver, and endometrium (hence the endometrial cancer risk during long-term female use). Listed on the WADA list (S4 hormone modulator) – banned in competitive sport.
Mechanism
Non-steroidal SERM, ER-α competitive antagonist at pituitary + breast
Dosing (PCT)
20-40 mg/day, 4-6 weeks
Half-life
~5-7 days (parent) / ~14 days (4-OH-tamoxifen active metabolite)
Onset
LH rise within 24-72 h, Test recovery 2-3 weeks
Legal status
FDA + EMA Rx, registered in HU + PL, WADA S4 (banned in-competition)
Data console
Lab data
Safety
Side effects, stop signs, contraindications
Side effects · 7
- Venous thromboembolism (deep vein thrombosis, pulmonary embolism, stroke) – tamoxifen's most serious, FDA boxed-warning risk; prothrombotic via partial estrogen-agonist activity.
- Visual disturbances: scintillating scotoma, retinopathy, corneal/retinal crystalline deposits and cataract risk – dose-dependent, more common at higher doses, usually reversible on discontinuation.
- Mood swings, hot flushes, headache and flu-like feelings – arising from estrogen-receptor modulation and E2 fluctuation; in PCT a by-product of the HPTA restart.
- Mild, usually transient liver enzyme elevation (ALT/AST); with rare chronic high-dose use severe hepatotoxicity, steatosis and cirrhosis are documented – clinically rare at the 4-6 week PCT dose.
- Endometrial hyperplasia, polyps and endometrial carcinoma risk (partial agonist effect on the uterine lining) – primarily in women on long-term use; also an FDA boxed warning.
- Reduced therapeutic effect in CYP2D6 poor-metabolizers (about 7-10% of Caucasians) and with strong CYP2D6-inhibitor SSRIs (paroxetine, fluoxetine) co-administered – active endoxifen levels drop dramatically.
- Reduced IGF-1 levels (~10-15%), fatigue and slower recovery – due to partial blockade of the hepatic IGF-1 signaling pathway; reversible 4-6 weeks after PCT ends.
Contraindications · 7
- Pregnancy and breastfeeding (Pregnancy Category D) – teratogenic, risk of fetal harm and miscarriage; reliable non-hormonal contraception required during and after treatment.
- Active or prior venous thromboembolism (deep vein thrombosis, pulmonary embolism) in history, and concurrent coumarin-type anticoagulant therapy – substantially increased clotting risk.
- History of endometrial hyperplasia or endometrial carcinoma – the partial agonist effect causes a 2-3 fold relative risk increase.
- Known hypersensitivity to tamoxifen or any excipient of the product.
- Severe liver disease or uncontrolled hyperlipidemia/hypertriglyceridemia – tamoxifen can rarely provoke severe hypertriglyceridemia and pancreatitis.
- Concurrent strong CYP2D6-inhibitor SSRIs (paroxetine, fluoxetine) – they block active endoxifen conversion, potentially rendering tamoxifen ineffective; if an SSRI is needed, choose venlafaxine or citalopram.
- Competitive sport under WADA ban (S4.3 hormone and metabolic modulator) – prohibited both in- and out-of-competition, with a 2-3 month urine detection window.
Related Performance Compounds
Same therapeutic category
Studies
Related research and clinical findings
Tamoxifen for prevention of breast cancer: report of the National Surgical Adjuvant Breast and Bowel Project P-1 Study
Fisher B, Costantino JP, Wickerham DL, et al.
50th anniversary of the first clinical trial with ICI 46,474 (tamoxifen): then what happened?
Jordan VC
Anabolic steroid-induced hypogonadism: diagnosis and treatment.
Rahnema CD, Lipshultz LI, Crosnoe LE, Kovac JR, Kim ED
Enclomiphene citrate: A treatment that maintains fertility in men with secondary hypogonadism.
Earl JA, Kim ED
CYP2D6 genotype, antidepressant use, and tamoxifen metabolism during adjuvant breast cancer treatment.
Jin Y, Desta Z, Stearns V, Ward B, Ho H, Lee KH, Skaar T, Storniolo AM, Li L, Araba A, Blanchard R, Nguyen A, Ullmer L, Hayden J, Lemler S, Weinshilboum RM, Rae JM, Hayes DF, Flockhart DA
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