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Prostate Drug Dutasteride Shrinks Prostate and Penis

Dutasteride shrinks prostate glands but it also has sexual side effects. It can cause diminished libido & block sexual satisfaction. What about penis size?

Dutasterice (Avodart) has a powerful effect on the prostate gland. The history of this medication and its chemical cousin finasteride (Proscar) is a medical mystery. It all started in the Dominican Republic over 40 years ago. Researchers reported on a number of male pseudohermaphrodites (Science, Dec. 27, 1974).  They were “born with ambiguity of the external genitalia.” Their levels of dihydrotestosterone (DHT) were low because the activity of the enzyme 5a-reductase was also low. This discovery led to the development of finasteride, a drug that shrinks prostate glands.

How Do Inhibitors of 5-alpha Reductase Work?

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 prostate problems and they didn’t develop male pattern baldness.

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 approval and was marketed to shrink enlarged prostates in 1992. It took some time to learn about side effects from finasteride and Dutasteride.

Finasteride Shrinks Prostate and Lowers PSA:

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.

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Stories from Readers:

Michael reports a similar complication:

“After taking Dutasteride for four years I have suffered penis shinkage, 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 dutasteride and finasteride 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 prostrate 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.”

Dutasteride and Diabetes:

A study published in The BMJ (April 10, 2019) reported that men taking either dutasteride or finasteride were slightly more likely to develop type 2 diabetes.  Dutasteride increases insulin resistance.

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About the Author
Terry Graedon, PhD, is a medical anthropologist and co-host of The People’s Pharmacy radio show, co-author of The People’s Pharmacy syndicated newspaper columns and numerous books, and co-founder of The People’s Pharmacy website. Terry taught in the Duke University School of Nursing and was an adjunct assistant professor in the Department of Anthropology. She is a Fellow of the Society of Applied Anthropology. Terry is one of the country's leading authorities on the science behind folk remedies..
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