Enarei

Tamoxifen

Tamoxifen is selective estrogen receptor modulator (SERM). This means it has the same effect as estrogen in most of the body, but has the opposite effect in some areas, including the breasts. Tamoxifen is similar to Raloxifene, but is much less safe, and possibly less effective. (Xu et al., 2021). Nonetheless, it is sometimes used by people who self-medicate for such reasons as price and availability.

Trans people (particularly non-binary people) sometimes take tamoxifen with the aim of inducing feminization without breast development (Aly, 2019). This is usually done instead of- or along with estrogen and/or testosterone blockers.

Tamoxifen regimens are experimental, and there is only minimal data available on whether they work well, or are safe in the long term. No prescriber guidelines currently recommend their use, although this was also once true of all other transgender hormone regimens.

Unlike estrogen, tamoxifen does not lower testosterone production. Instead, it significantly increases testosterone levels in people who were assigned male at birth. This means that tamoxifen may cause unwanted masculinization if It is not combined with testosterone blockers or surgery. (Birzniece et al., 2010).

Compared to raloxifene, tamoxifen is usually less preferred because it is much more dangerous without providing any benefit. Nonetheless, it is sometimes used by people who self-medicate for such reasons as price and availability.

Key points

  • An older and much more dangerous form of raloxifene that should be avoided where possible
  • Experimentally used for feminization without breast development
  • Works like estrogen in most of the body, but has the opposite effect in the breasts
  • Minimal information on efficacy and safety
  • No standardized regimens
  • Combining with calcium, vitamin D, and healthy lifestyle may reduce risks
  • Combining with testosterone blocking treatment necessary to avoid unwanted masculinization
  • Requires ongoing liver function monitoring and complete blood counts
  • Sometimes used by people who self-medicate, only rarely prescribed

Dosing

Tamoxifen is a pill (or rarely liquid) that is swallowed. It is most commonly used at a dose of 20 - 40 mg once daily, but different dosages are sometimes used, particularly by people who self-medicate. (AstraZeneca, 2009).

Risks & management

Tamoxifen may increase the risk of blood clots and stroke. This is especially important to remember when combining it with other drugs that also increase this risk, such as cyproterone acetate and oral estrogen pills. Tamoxifen increases these risks more than Raloxifene (Vogel et al., 2006).

Raloxifene significantly increases testosterone production in people who are assigned male at birth. This could cause unwanted masculinization if not offset using other medications, and it is therefore advisable to monitor testosterone levels when taking tamoxifen. Tamoxifen increases this risk more than Raloxifene (Birzniece et al., 2010).

Regimens that involve tamoxifen may increase the risk of developing problems with low bone density. Tamoxifen may increase this risk more than raloxifene (Xu et al., 2021).

Tamoxifen has a very small risk of causing life-threatening injury to the liver. When taking tamoxifen, it is extremely important that liver function is regularly checked using such blood tests as "alanine aminotransferase" (ALT). The manufacturer also recommends periodic complete blood counts (AstraZeneca, 2009).

In the short-term, hormone regimens involving tamoxifen are likely relatively safe, though they may cause menopausal symptoms such as hot flashes. In the long term, their safety is unstudied, with concerns long-term use could carry significant negative health effects. There is little concrete data available on this (Xu et al., 2021).

Interactions

Tamoxifen may become less effective when taken with a wide variety of other medications, including many common antidepressants (Jin et al., 2005).

Other information

Tamoxifen is rarely prescribed in formal healthcare settings due to limited data and lack of prescriber guidelines. Most people who use raloxifene are self-medicating.

Tamoxifen is also called "Nolvadex", or simply "tamox".

See also

References

  • Aly. (2019). An Exploration of Possibilities for Hormone Therapy in Non-Binary Transfeminine People. Transfeminine Science. [URL]
  • AstraZeneca. (2009). Nolvadex: Highlights of prescribing information. [PDF]
  • Birzniece, V., Sata, A., Sutanto, S., & Ho, K. K. (2010). Neuroendocrine regulation of growth hormone and androgen axes by selective estrogen receptor modulators in healthy men. The Journal of clinical endocrinology and metabolism, 95(12), 5443–5448. [DOI:10.1210/jc.2010-1477]
  • Jin, Y., Desta, Z., Stearns, V., Ward, B., Ho, H., Lee, K. H., Skaar, T., Storniolo, A. M., Li, L., Araba, A., Blanchard, R., Nguyen, A., Ullmer, L., Hayden, J., Lemler, S., Weinshilboum, R. M., Rae, J. M., Hayes, D. F., & Flockhart, D. A. (2005). CYP2D6 genotype, antidepressant use, and tamoxifen metabolism during adjuvant breast cancer treatment. Journal of the National Cancer Institute, 97(1), 30–39. [DOI:10.1093/jnci/dji005]
  • Vogel, V. G., Costantino, J. P., Wickerham, D. L., Cronin, W. M., Cecchini, R. S., Atkins, J. N., Bevers, T. B., Fehrenbacher, L., Pajon, E. R., Jr, Wade, J. L., 3rd, Robidoux, A., Margolese, R. G., James, J., Lippman, S. M., Runowicz, C. D., Ganz, P. A., Reis, S. E., McCaskill-Stevens, W., Ford, L. G., Jordan, V. C., … National Surgical Adjuvant Breast and Bowel Project (NSABP) (2006). Effects of tamoxifen vs raloxifene on the risk of developing invasive breast cancer and other disease outcomes: the NSABP Study of Tamoxifen and Raloxifene (STAR) P-2 trial. JAMA, 295(23), 2727–2741. [DOI:10.1001/jama.295.23.joc60074]
  • Xu, J. Y., O'Connell, M. A., Notini, L., Cheung, A. S., Zwickl, S., & Pang, K. C. (2021). Selective Estrogen Receptor Modulators: A Potential Option For Non-Binary Gender-Affirming Hormonal Care?. Frontiers in endocrinology, 12, 701364. [DOI:10.3389/fendo.2021.701364]