Afimoxifene

Afimoxifene (4-hydroxytamoxifen; TamoGel) is a SERM. It is one of the active metabolites of tamoxifen. It is delivered topically as a gel that is applied directly to the breast. Unlike oral SERMs such as tamoxifen or raloxifene, it is not highly systemic: its effects are mostly local to the breast.

Application to non-binary transition
Some non-binary people desire feminization without breast growth, and Afimoxifene may be an option for them. It may allow AMAB people to take an antiandrogen and/or estrogen while preventing breast growth and/or tenderness, and allow the same for AFAB people who would otherwise experience the same due to puberty.

Open question
Does afimoxifene prevent breast growth in people with female-typical estrogen levels? There is some evidence that it might, as it has been shown to effectively treat moderate-to-severe breast pain in premenopausal women.

Availability
Not generally available. As of 2017, it is only available from research chemical suppliers.

Safety
Uncertain. As of 2017, there have been no large scale clinical trials.

Speculation
'The following is speculation. There is no experimental evidence to support this.'

It is unlikely to have any side effects that tamoxifen doesn't have, as tamoxifen metabolizes into afimoxifene in the body. Furthermore, because it is not highly systemic, it is unlikely to have side effects in areas other than the breast.

Tamoxifen is a known carcinogen in uterine tissue. While the low systemicity of topical afimoxifene suggests that the risk of cancer would be lower than that of tamoxifen, it would be good to exercise caution, especially in those with a uterus.