Xenoestrogen
Xenoestrogens are a type of xenohormone that imitates estrogen. They can be either synthetic or natural chemical compounds. Synthetic xenoestrogens include some widely used industrial compounds, such as PCBs, BPA, and phthalates, which have estrogenic effects on a living organism even though they differ chemically from the estrogenic substances produced internally by the endocrine system of any organism. Natural xenoestrogens include phytoestrogens which are plant-derived xenoestrogens. Because the primary route of exposure to these compounds is by consumption of phytoestrogenic plants, they are sometimes called "dietary estrogens". Mycoestrogens, estrogenic substances from fungi, are another type of xenoestrogen that are also considered mycotoxins.
Transgender hormone therapy (female-to-male)
Synthetic anabolic–androgenic steroids (AAS), like nandrolone (as an ester like nandrolone decanoate or nandrolone phenylpropionate), are agonists of the androgen receptor (AR) similarly to testosterone but are not usually used in HRT for transgender men or for androgen replacement therapy (ART) in cisgender men. However, they can be used in place of testosterone with similar effects, and can have certain advantages like less or no local potentiation in so-called androgenic tissues that express 5α-reductase like the skin and hair follicles (which results in a reduced rate of skin and hair-related side effects like excessive body hair growth and scalp hair loss), although this can also be disadvantageous in certain aspects of masculinization like facial hair growth and normal body hair growth). Although many AAS are not potentiated in androgenic tissues, they have similar effects to testosterone in other tissues like bone, muscle, fat, and the voice box. Also, many AAS, like nandrolone esters, are aromatized into estrogens to a greatly reduced extent relative to testosterone or not at all, and for this reason, are associated with reduced or no estrogenic effects (e.g., gynecomastia). AAS that are 17α-alkylated like methyltestosterone, oxandrolone, and stanozolol are orally active but carry a high risk of liver damage, whereas AAS that are not 17α-alkylated, like nandrolone esters, must be administered by intramuscular injection (via which they act as long-lasting depots similarly to testosterone esters) but have no more risk of liver damage than does testosterone.