The U.S. National Institute of Health (NIH) has published information for those suffering from side effects of Propecia, sometimes referred to as post-finasteride syndrome.

The NIH’s Genetic and Rare Diseases Information Center reports researchers are now studying adverse events reportedly associated with a class of drugs including Propecia. Patients taking these drugs have reported Propecia side effects of “sexual outcomes, breast outcomes, and depression,” according to the NIH.

Propecia is a brand name for the drug finasteride, used as a treatment for male-pattern hair loss, also known as androgenic alopecia. The same drug was originally sold under the brand name Proscar as a treatment for benign prostatic hypertrophy (or enlarged prostate gland). After five years on the market for that use, the FDA approved finasteride under the name Propecia as a treatment for androgenic alopecia.

Finasteride works by blocking the action of 5-alpha reductase(DHT), an enzyme that converts testosterone into dihydrotestosterone. Enlargement of the prostate gland depends on the presence of DHT; finasteride reduces that enlargement by decreasing the amount of DHT in the prostate.

DHT may also have a role in male-pattern baldness. Men with that condition have more DHT than normal in their balding scalp. By blocking the creation of DHT, finasteride seems to inhibit the mechanism that leads to baldness.

Propecia Side Effects

According to the Post-Finasteride Syndrome Foundation, some users of Propecia and Proscar suffer a particular set of harmful side effects. Propecia side effects may include erectile dysfunction, decreased libido, anxiety, and depression. Clinical trials for Propecia showed similar results, with a small percentage of Propecia patients reporting decreased libido, erectile dysfunction, or ejaculation disorder.

The Post-Finasteride Syndrome Foundation also says some Propecia users have experienced “Peyronie’s disease, penile shrinkage, gynecomastia, muscle atrophy, cognitive impairment, insomnia, severely dry skin and tinnitus.” According to the Foundation, patients with post-finasteride syndrome are at risk for other negative effects throughout their lives, such as job loss, breakup of romantic relationships, and in some cases suicide.

Past clinical trials intended to evaluate the safety of Propecia have been called into question. In a study published in the Jund 2015 edition of JAMA Dermatology, researchers determined that none of 34 clinical trials for finasteride as a treatment for androgenic alopecia provided adequate reporting of safety information. The study also revealed evidence of bias: more than half of the trials disclosed conflicts of interest, and more than half received funding from the drug’s manufacturer. The researchers concluded that the information produced by these clinical trials is insufficient to determine the safety profile for finasteride as a treatment for androgenic alopecia.

The same study noted that 26 of the 34 trials for finasteride as a hair loss treatment observed treatment for one year or less. One trial for Proscar, however, involved four years’ worth of observation. In this placebo-controlled study known as PLESS, 3.7 percent of patients discontinued Proscar due to some sort of sexual dysfunction. Patients reported impotence, decreased libido, decreased volume of ejaculate, ejaculation disorder, breast enlargement, breast tenderness, and rash.