17-α-Estradiol (also called alfatradiol) is a weak synthetic estrogen and a close structural relative of the main female sex hormone estradiol. In contrast to estradiol, however, 17-α-estradiol has only very little hormonal effect. The inactive hormone is described as an inhibitor of the enzyme 5-α reductase, which converts testosterone into DHT. However, this characterization is based on only one source, which investigated the effect of the substance on 5-α reductase in rat liver .
17-α-Estradiol is a component of freely available tinctures (Ell-Cranell alpha, Pantostin) for local application in cases of (especially female) androgenetic alopecia. However, its effect against hair loss has only been investigated in a few studies.
Two relatively isolated publications from 1980 and 2005 found that the substance increased the proportion of anagen hair in the majority of users after several months of application (other parameters such as hair density or thickness were not investigated).  A study from 2007 compared alfatradiol and minoxidil – and attested minoxidil the far better efficacy.  In this study, alfatradiol was able to prevent further hair loss with regular application, but did not cause new hair to grow.
In a study from Korea published in 2012, Ell-Cranell alpha increased the number of hairs on a square centimetre of scalp in 56 women with androgenetic alopecia after eight months of regular use from an average of 323 to an average of 355 and also caused the average hair diameter measured in the phototrichogram to increase noticeably (the comparison with placebo in a double-blind study – gold standard of scientific research, did not exist here). The overall picture of the hair was described by the investigators on the basis of photos as slightly (40%), moderately (22%) or significantly (18%) improved in 80% of the test subjects. However, the women themselves were rather dissatisfied: Here, 66% were of the opinion that the product had not achieved anything in all .