Nolvadex (Tamoxifen)
Tamoxifen · Nolva · SERM
SERM used in PCT and on-cycle gynecomastia management. Active metabolite endoxifen.
Key takeaways
- Blocks estrogen at the breast receptor directly; the standard SERM for gyno and PCT.
- Parent half-life ~47 hours; active metabolite endoxifen (via CYP2D6) lasts far longer.
- CYP2D6 inhibitors and poor-metabolizer genotypes blunt endoxifen formation and effect.
- Key risks are thromboembolic events and, with long use, rare endometrial effects.
Overview
What it is
Nolvadex (tamoxifen) is a selective estrogen receptor modulator approved for estrogen-receptor-positive breast cancer, and the standard SERM for post-cycle therapy and on-cycle gynecomastia management. It blocks estrogen at the breast receptor while acting as a partial agonist in bone and liver.
Pharmacokinetics
The parent half-life is roughly 47 hours, but the active metabolite endoxifen (formed via CYP2D6) lasts far longer, so once-daily dosing builds a durable steady state over weeks. The dataset uses roughly 15% oral bioavailability.
What the evidence says
Tamoxifen's oncology evidence spans decades of randomized trials. For gynecomastia it targets the breast receptor directly instead of crashing systemic estradiol, which is why it's preferred over aromatase inhibitors for that job. The real risks are thromboembolic events and, with extended use, rare endometrial effects. CYP2D6 inhibitors and poor-metabolizer genotypes blunt endoxifen formation and reduce its effect.
Reported dosing protocols
Protocols reported in research literature and clinic/community use — informational context, not a dosing recommendation.
| Use case | Dose | Route | Frequency | Duration |
|---|---|---|---|---|
| Breast cancer (label) | 20–40 mg | Oral | Once daily | 5–10 years (adjuvant) |
| PCT (community) | 20–40 mg | Oral | Once daily | 4–6 weeks |
| Gynecomastia on-cycle (community) | 10–20 mg | Oral | Once daily | Until symptoms resolve |
Pharmacokinetic summary
- Model tier
- Advanced (t½ + Cmax + Tmax + F)
- Half-life
- 47.4 hours
- Cmax
- 200 ng/mL
- Tmax
- 0.3 days
- Bioavailability
- 15%
- Typical dose
- 10–40 mg
Frequently asked questions
Why tamoxifen instead of an AI for gynecomastia?
Tamoxifen blocks estrogen directly at the breast receptor, so it treats gyno symptoms without crashing systemic estradiol and the joint, libido, and lipid problems that come with that. AIs reduce estrogen everywhere; tamoxifen targets the tissue that matters here.
Does tamoxifen interact with antidepressants?
Yes, meaningfully. Strong CYP2D6 inhibitors like paroxetine and fluoxetine block conversion to endoxifen, the metabolite carrying much of its effect, and poor-metabolizer genotypes have the same problem. It's a documented, clinically relevant interaction.
How long does a tamoxifen PCT last?
Community protocols typically run 4–6 weeks at 20–40 mg daily, sometimes tapered, starting after exogenous compounds clear. Whether any PCT speeds true recovery isn't settled by trials; bloodwork over the following months is the real check.
References
- FDA Nolvadex biopharm review
- FDA Nolvadex biopharmaceutics review — Regulatory PK and bioavailability summary behind the plotter model.
Related compounds
Clomid (Clomiphene)
SERM that blocks hypothalamic estrogen receptors, boosting LH/FSH; primary PCT agent.
Estradiol Topical (EstroGel)
Transdermal estradiol for feminizing HRT. Steady low-level delivery.
Estradiol Cypionate
Injectable estradiol cypionate used in feminizing HRT.
Protocols featuring Nolvadex (Tamoxifen)
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