17α-Estradiol is the natural optical isomer of 17β-estradiol , the major estrogen secreted by the premenopausal ovary. 17α-Estradiol is a less active isomer than its counterpart, displaying 100-fold lower estrogenic activity relative to 17β-estradiol.¹ It can inhibit 5α-reductase, which plays a role in regulating hair growth. 17α -estradiol is reported to activate the MAPK/ERK and PI3K-Akt signaling pathways via activation of the estrogen receptor-X and has been shown to be neuroprotective after an ischemic stroke and oxidative stress and in transgenic mice with Alzheimer’s disease.^1,2