As I involve myself in the biology underlying the finasteride and post-finasteride-associated hypogonadal syndrome and parallel "brain fog" syndrome many men experience, I have focused on the metabolism of dihydrotestosterone (DHT), the hormone that finasteride inhibits by virtue of its blockage of the 5-alpha reductase enzyme that normally converts testosterone to DHT (along with several other reactions it normally does that form potent neuroactive anti-anxiety and seizure preventing hormones in the brain). Moreover, I have written here about the role of estrogen in the brains of women (e.g. cognition, neuroprotection) and the fact that we men need estrogen in our brains also. We get it by converting testosterone to estrogen in brain cells by a different enzyme called aromatase. One might think these two pathways for testosterone conversion, one to DHT and one to estrogen, are separate and distinct. Interestingly, several brain areas important for controlling male sexual behavior use estrogen derived from testosterone.
When a man takes finasteride to block DHT and save his hair, he is likely unaware of the complexity of this hormone's actions involving sexual behavior, stress responses, cognition and more. However, a study I recently read, Handa, RJ et al. Hormones and Behavior 53 (2008) 741-752, describes an alternative pathway for androgen regulation of brain function by estrogen receptors triggered by metabolites of DHT. In other words DHT, 10 times more potent than testosterone, can itself be converted to compounds that bind estrogen receptors (ERbeta) but are not estrogen. One of these, called 3-alpha Diol, is also a neuroactive steroid that enhances the inhibitory compound GABA in the brain (like benzodiazepines and barbituates). Another, called 3-beta Diol, can act through estrogen receptors to decrease anxiety and regulate the cortisol system's response to stress. Without going into too much detail here, the important point is that DHT is involved in a number of metabolic pathways in the brain that create androgen-related and estrogen-related compounds that have effects on all these areas of behavior, some as promoters and others as inhibitors, some at androgen sites and others at estrogen sites, and, in at least a subset of men, interfering with this complex web of reactions by blocking DHT, may bring a lot of unwanted extra effects along with the preservation of hair.