Tamoxifen is a selective estrogen receptor modulator (SERM): it blocks estrogen's action in some tissues, such as breast tissue, and mimics it in others. It is sold as generic tablets and as Soltamox oral solution.
Also known as: Nolvadex, Soltamox.
Generic tamoxifen citrate tablets come in 10 mg and 20 mg strengths. Soltamox is an oral solution.
The FDA label approves tamoxifen for breast cancer: treatment of metastatic breast cancer in women and men, adjuvant treatment after breast cancer surgery, reducing the risk of invasive breast cancer in women with ductal carcinoma in situ (DCIS), and reducing breast cancer incidence in women at high risk. For breast cancer the labeled dose is 20 to 40 mg daily, with doses above 20 mg split into morning and evening; for DCIS and risk reduction it is 20 mg daily for 5 years.
The label carries a boxed warning for women with DCIS and women at high risk: uterine cancers, stroke and pulmonary embolism, some of them fatal. It also says tamoxifen can strongly increase the effect of warfarin-type blood thinners.
In men on TRT, tamoxifen is used off-label, for example for breast tissue growth (gynecomastia). The American Urological Association 2018 guideline says clinicians may use SERMs, hCG or aromatase inhibitors in men with testosterone deficiency who want to maintain fertility (a conditional recommendation), and notes that only hCG is FDA approved for use in males. Whether to take it, and how much, is a decision for you and your prescriber. See also clomiphene and enclomiphene, the other SERMs on this site.
The FDA tamoxifen label says levels fall in two phases, with a terminal elimination half-life of about 5 to 7 days; Dose Track uses 6 days. Its main active metabolite, N-desmethyl tamoxifen, has a half-life of about 14 days, and steady state takes about 4 weeks for tamoxifen and about 8 weeks for the metabolite. After a single 20 mg dose, peak levels came about 5 hours later; Dose Track uses 5 hours.
Numbers shown are the values Dose Track uses, listed only where they agree with the source above. Half-life varies from person to person and with injection site.