Michael S. Irwig MD, who works at the Center for Andrology and Division of Endocrinology, The George Washington University, Washington, DC, prospectively monitored 54 adult males, average age 31, who had had three or more months of finasteride-associated sexual side effects. A side effect that continues for over three months is described as "persistent".
All the men were healthy at the start of the study, and had never had any problems with sexual functions; they had no medical or psychiatric conditions and had not used oral prescription drugs before taking Propecia for male pattern hair loss.
All the men in this study were checked and rechecked for 14 months.
96% of those who were reassessed still had persistent sexual side effects; some of them also had changes in cognition, genital sensation, and ejaculate quality.
Dr. Irwig found that 89% of the 54 men met the Arizona Sexual Experiences Scale (ASEX) of sexual dysfunction, which rates sex drive (libido), arousal, penile erection, ability to orgasm, and orgasm satisfaction.
In an Abstract in the same journal, Dr. Irwig concluded:
"In most men who developed persistent sexual side effects (≥3 months) despite the discontinuation of finasteride, the sexual dysfunction continued for many months or years.
Although several rat studies have shown detrimental changes to erectile function caused by 5 alpha reductase inhibitors, the persistent nature of these changes is an area of active research.
Prescribers of finasteride and men contemplating its use should be made aware of the potential adverse medication effects."
What is Propecia (finasteride)?Finasteride is a synthetic 5α-reductase inhibitor. It is an inhibitor of the enzyme that coverts testosterone to DHT (dihydrotestosterone). It is produced and marketed by Merck & Co., Inc. It is known under the brand names Proscar and Propecia and has been approved by the FDA for the treatment of:
- Male pattern baldness - hair is lost in a well defined pattern, starting above the temples and thinning at the crown of the head.
- Benign prostatic hyperplasia - an increase in the size of the prostate
- Erectile dysfunction (impotence)
- Abnormal ejaculation
- Lower ejaculatory volume
- Abnormal sexual function
- Testicular pain
- Gynecomastia - development of male breasts
- Depression - Merck added this side effect in December 2010
A 2008 study found that finasteride reduces prostate cancer risk without boosting the chances of developing aggressive tumors. (Link to article)
A 2010 study suggested that finasteride use is linked to male breast cancer risk. (Link to article)