5α-reductases are a family of isozymes that play a critical role in transformation not only of testosterone but also of progesterone, DOC, aldosterone, and cortisol into a host of neuro-active steroids that regulate a multitude of functions in human physiology… the neuro-active steroid hormones modulate a multitude of functions in human physiology encompassing regulation of sexual differentiation, neuroprotection, memory enhancement, anxiety, sleep, and stress, among others. Until recently, the adverse effects of 5α-reductase inhibitor therapy were thought to be very minor and well tolerated. However, new information suggests that these drugs may impair sexual function including sexual desire, erectile and orgasmic function. Recent studies in animal models suggested that these agents alter penile tissue histo-architecture and nitric oxide synthase function in penile tissue and thus can contribute to erectile dysfunction. It is particularly important to note that in a subset of patients, the effects of these drugs are long-lasting and may be irreversible. An association between the use of these inhibitors and depression is also noted, suggesting a potential adverse effect on the brain.
Traish, AM. 5α-reductases in human physiology: an unfolding story. Endocr Pract. 2012 Nov-Dec;18(6):965-75. doi: 10.4158/12108.RA. [PubMed]