Estrogens

Estradiol is the main active estrogen in our bodies, and has a much higher binding affinity than estrone, so that is the one we will use for feminizing HRT. There are also a number of synthetic estrogens, developed by pharmaceutical laboratories in particular for the use in birth control pills: a common one is Ethinylestradiol (EE). As a synthetic derivative of estradiol, EE also comes with more (and more frequent) side effects. This is why it is not recommended to use birth control pills for feminizing HRT. Actually, research has shown that the common side effects of estrogen therapy that trans women are usually warned about by practitioners - and used as a reason to keep them at low doses of estrogens - such as blood clots, are mostly associated to synthetic estrogens (like EE), and to a much lesser extent to bioidentical estradiol.

Target range

A serum level of 200 to 300 pg/ml is usually enough to activate the negative feedback and efficiently reduce the production of testosterone. If are not on monotherapy, the same range also seems to be a target for most transfem people in order to keep a good mood and energy. However, keep in mind that those values can change between individuals, and the best remains to do blood work, and be attentive to how you feel.

This is especially true for the threshold of “overdosing”, which can vary a lot between individuals. Some trans women need higher doses (between 350 and 600 pg/ml) to feel good, when others will have symptoms of overdose at these levels (headaches, nausea, heavy legs). Find what is good for you, when you feel energized, and don’t hesitate to try to get higher levels if you feel symptoms of underdose (tiredness and fatigue, low morale, hot flushes, complete lack of libido…).

Do not assume this is just your mood and do not normalize it. Adjusting your levels CAN make a difference.

Summary of the different routes