This complex body of research can be thought of in phases:
The development of finasteride by Merck was inspired by a 1974 paper reporting on individuals with atypical sexual development in a remote village in the Dominican Republic. The paper, by Julianne Imperato-McGinley and colleagues, was titled ‘Steroid 5alpha-reductase deficiency in man: an inherited form of male pseudohermaphroditism‘. When these individuals matured, they did not have enlarged prostates nor recession of their hairline. The lack of expression of these typically male traits was attributed to a deficiency in the enzyme 5-alpha reductase (5-AR). Imperato-McGinley went on to publish dozens of papers on 5-alpha reductase deficiency and related topics.
For narrative accounts of research on male pseudohermaphrodies, see Sources on the early history of finasteride.
Drug development and Proscar approval, 1981–1992
In the 1980s, inhibition of the 5-alpha reductase enzyme was explored in animal studies.
The Finasteride Study Group published an article on finasteride for the treatment of benign prostatic hyperplasia (BPH) in New England Journal of Medicine in 1992. Also in 1992, FDA approved Merck’s application for Proscar (finasteride, 5 mg/day) for the treatment of BPH.
Propecia development and approval, 1992–1997
In the mid-1990s, trials were run on finasteride for androgenetic alopecia culminating in FDA approval of Propecia (finasteride, 1 mg/day) in late 1997.
Whereas Proscar was used by urologists to treat men 50 and older, Propecia would be used by dermatologists to treat hair loss in much younger men, 18 and older.
Quiet period, 1998–2009
Following approval of Propecia, there was a slow trickle of papers, averaging about 9 per year. During this period, finasteride was studied as a treatment to prevent prostate cancer. GSK developed another 5-alpha reductase inhibitor, dutasteride, which was approved as Avodart for the treatment of BPH.
Concerns about persistent adverse effects and ‘post-finasteride syndrome’, 2010–present
In 2010–2011, several papers raised concerns about adverse effects of finasteride, including those reported to continue after stopping the medication.
This period saw increased attention to adverse effects of finasteride as measured by papers per year, with nearly 50 papers published in 2020. Whereas earlier papers came from the fields of urology and dermatology, research during this period brought new perspectives including genetics, neuroendocrinology and epidemiology.
In July 2021, a study reporting altered gene expression in PFS patients was published in the Journal of Sexual Medicine: Howell S et al. Differential Gene Expression in Post-Finasteride Syndrome Patients.
See also: a more general timeline on the history of finasteride and 5-alpha reductase inhibitors.