The FDA approved finasteride (Proscar) to treat BPH (benign prostatic hyperplasia) in 1992. Then it gave dutasteride (Avodart) the green light for enlarged prostates in 2001. The history of these medications started with a medical mystery. It all began in the Dominican Republic over 70 years ago. Researchers reported on a number of male pseudohermaphrodites (Science, Dec. 27, 1974). These babies were “born with marked ambiguity of the external genitalia.” Their levels of dihydrotestosterone (DHT) were low because the activity of the enzyme 5α-reductase was also low. More about that momentarily. Bottom line: finasteride and dutasteride shrink the prostate gland…and potentially the penis.
When Sex Is Ambiguous:
Most people think that it’s easy to tell what sex a baby is. You just look at the external genitals and it is supposed to be obvious. But that is not always the case. The physician researchers (endocrinologists and a pediatrician wrote up their investigation in technical terms (Science, Dec. 27, 1974), but you, dear Reader, can probably figure this out if you try:
“To date we have found 13 families with 24 pseudohermaphrodites, in the village of Salinas in the Dominican Republic. The affected males (46 XY) are born with marked ambiguity of the external genitalia, and before the disorder became obvious to the community were raised as girls. At birth, they have bilateral testes presenting as inguinal or labial masses, a labial-like scrotum, a urological sinus with a blind vaginal pouch. No Mullerian structures are present.
“At puberty, their voice deepens and they develop a typical male phenotype with a substantial increase in muscle mass; there is no breast enlargement. The phallus enlarges to become a functional penis, and the change is so striking that these individuals are referred as “guevedoces”–penis at 12 (years of age). [literally, guevedoces translates to eggs or testicles at 12. These young men were also called “machihembras” or “first a woman, then a man.”]
“Psychosexual orientation (postpubertal) is male, and this is of considerable interest, since the sex of rearing in 18 of the affected males was female. Despite the sex of rearing, the affected were able to change gender identity at the time of puberty. They consider themselves as males and have a libido directed toward the opposite sex.”
Did you understand what happened? At birth, these babies appeared to be girls. There was no penis. The families raised these children as if they were female. But when they reached puberty, enough testosterone and its byproduct, dihydrotestosterone (DHT), were created to lead to male characteristics, including a penis.
The enzyme that converts testosterone to DHT is 5α-reductase. Because these babies had low levels of the enzyme 5α-reductase, they did not develop male genitalia until puberty when a sudden flood of testosterone could be converted to DHT even with limited amounts of the enzyme 5 alpha-reductase.
Unexpected Benefits of Low DHT Levels Led to Finasteride and Dutasteride:
The young people who started life with ambiguous genitals eventually turned into men. The low activity of the enzyme 5a-reductase had seeming benefits. The men never developed acne, prostate problems and they didn’t develop male pattern baldness. This was quite different from other men in the village.
Because the enzyme in question converts testosterone to DHT, scientists believed that it might offer a clue to treating men with these common problems. Merck attempted to mimic the genetic quirk in the laboratory. Finasteride inhibits the enzyme and interferes with the conversion of testosterone to DHT. It received FDA approval and was marketed to shrink enlarged prostates in 1992.
The oral drug Propecia (1 mg of finasteride) received approval from the FDA to treat male pattern baldness in 1997. The related compound, dutasteride, has only been approved for BPH, though some doctors also prescribe it off label for hair loss. Bottom line: reducing the activity of the enzyme 5α-reductase with finasteride or dutasteride can reduce symptoms of benign prostate enlargement and slow hair loss. That may sound like a double win…but there were some unexpected complications.
The Law of Unintended Consequences with Finasteride and Dutasteride:
`Please step into our time machine. We are going to fast forward from the 1990s to 2025. The Wall Street Journal writer, Rolfe Winkler, wrote an article on March 14, 2025 titled: “Side Effects Sickened Some Telehealth Hair-Loss Patients.“
The online version was titled:
“They Wanted a Quick Fix for Hair Loss. Instead, These Young Men Got Sick.”
The article quotes a professional:
“Dr. Justin Houman, a urologist at Cedars-Sinai Medical Center in Los Angeles, said he has seen a steady increase of young men, one or two a week, seeking treatment for finasteride’s sexual side effects. Some also experience panic attacks and suicidal thoughts, he said.
“The side effects are ‘very very common’ these days because the medicine is easier to get from telehealth companies, Houman said. He said the cosmetic benefits of finasteride are almost never worth the risks. ‘This is not something young men should take,’ he said.”
Do Finasteride and Dutasteride Affect Penis Size?
The People’s Pharmacy has always been a clearing house for drug stories. Since we started writing our syndicated newspaper column in 1978, people from all over the world have been sending us reports of adverse reactions as well as descriptions of medication benefits.
One that we were not expecting was reduced penis size associated with finasteride and dutasteride.
Finasteride Shrinks Prostate and Penis:
Q. I took finasteride for an enlarged prostate, and it has shrunk my genitals. In addition, I have lost sensation at climax. If I had known it would cost me my sex life, I would never have taken it.
A. Researchers recognize post-finasteride syndrome, consisting of sexual dysfunction, neuropsychiatric symptoms and physical changes after some men stop taking this drug (International Journal of Impotence Research, Feb. 14, 2025). They urge greater awareness of this problem. As you point out, being warned beforehand would be preferable.
Dutasteride Also Affects Sexualtiy:
Q. I have been taking dutasteride (Avodart) for almost 10 years. My PSA has stabilized between 3.25 and 3.75. This medication affected my ability to maintain an erection long enough to engage in intercourse. It has also reduced my penis size somewhat.
What I am more concerned about than the sexual aspect, however, is the long-term effect on my overall health. Are there any consequences I should be watching for? My doctor does not seem to have any information on this.
A. Dutasteride and a related drug, finasteride (Proscar), are approved for the treatment of an enlarged prostate gland (benign prostate hypertrophy or BPH). They work by blocking the enzyme that converts testosterone to dihydrotestosterone (DHT). DHT is largely responsible for prostate enlargement and male pattern baldness.
A review of adverse events reported to the FDA noted several side effects of these drugs. These included reduced libido, erectile dysfunction, orgasmic disorders, breast enlargement, fatigue, muscle weakness, fuzzy thinking and hearing loss (Urology, Oct. 2018).
There is no mention of penis shrinkage in the official prescribing information. There are, however, a bunch of sexual side effects including reduced orgasmic sensations, diminished libido and sexual arousal and erectile dysfunction.
More Stories from Readers About Finasteride and Dutasteride:
Michael reports a similar complication:
“After taking dutasteride for four years I have suffered penis shrinkage, erectile dysfunction and general libido loss. The problem is that if I stop taking the drug my BPH [benign prostate hypertrophy] returns, and urination problems become a pain.
“Basically you have to make a choice. One or the other. The doctors don’t own up to that fact but that’s the reality.”
Joe shared this story:
“I have had two operations for enlarged prostate. I have been on dutasteride for 6 years and am now on tamsulosin which does help prevent getting up every hour or so. This has resulted in a dramatic shrinking of the penis which is embarrassing and results in no more erections or orgasms. It bothers me mentally and physically.”
Jack also experienced problems with dutasteride and its chemical cousin finasteride:
“I have taken both finasteride and dutasteride over the past 15 years. I have experienced both a loss of libido and a considerable shrinking of an already modest size penis. I’m back where I was about 10 years of age. I have resigned myself to live with the problem, since I don’t want prostate trouble, but it does have an effect on one’s ego. I’m healthy enough to have sex and would love to be able to continue what was a very good sex life with my wife.”
Final Words on Finasteride and Dutasteride:
Doctors sometimes have a hard talking about the sexual side effects of drugs. A physician who prescribes finasteride or dutasteride to treat BPH may not always mention that such drugs may mess up a man’s sex life.
Researchers reported in the New England Journal of Medicine, Oct. 22, 1992 that there was:
“a higher incidence of decreased libido, impotence, and ejaculatory disorders in the finasteride-treated groups.”
An article in the journal Sexual Medicine (July 14, 2022) describes “Post-Finasteride Syndrome” or PFS:
“PFS is a constellation of sexual, physical, and neurologic symptoms associated with 5-ARIs [5-α-reductase inhibitors] that may persist after discontinuation of the drug…which can have profound systemic effects such as: loss of libido, ED, ejaculatory disorders, gynecomastia, muscle atrophy, fatigue, depression, anxiety, cognitive impairment, and suicidal ideation.”
You can read about other reports of sexual side effects associated with finasteride and dutasteride at these links:
“Drug for Prostate Made Penis Shrink”
“Dutasteride and Depression | A Dark Side of Prostate Drugs like Avodart”
Dutasteride (Avodart) Sexual Side Effects Can Be Daunting
Please share your own experience with dutasteride and finasteride in the comment section below.
Citations
- Imperato-McGinley, J., et al, "Steroid 5α-Reductase Deficiency in Man: An Inherited Form of Male Pseudohermaphroditism," Science, Dec. 27, 1974, DOI: 10.1126/science.186.4170.1213
- Choi, G-S., et al, Annals of Dermatology, "Long-Term Effectiveness and Safety of Dutasteride versus Finasteride in Patients with Male Androgenic Alopecia in South Korea: A Multicentre Chart Review Study," Annals of Dermatology, Sept. 27, 2022, doi: 10.5021/ad.22.027
- Cilio, S., et al, "Post-finasteride syndrome - a true clinical entity?," International Journal of Impotence Research, Feb. 14, 2025, doi: 10.1038/s41443-025-01025-6
- Coskuner, E.R., et al, "Sexual Problems of Men With Androgenic Alopecia Treated With 5-Alpha Reductase Inhibitors," Sexual Medicine Reviews, April, 2019, doi: 10.1016/j.sxmr.2018.07.003
