Jul 30, 2018 3 min read

Dear Doctor: My husband’s doctor prescribed finasteride to treat his enlarged prostate, and he’s been taking it for years. Gradually, the side effects became noticeable, specifically erectile dysfunction. Shouldn’t men be warned about this? Aren’t there other options for an enlarged prostate?

Dear Reader: Erectile dysfunction is often a side effect of medications. Finasteride (trade name Proscar) is no different. It inhibits the 5-alpha-reductase enzyme that converts testosterone to the hormone dihydrotestosterone (DHT). DHT stimulates the prostate gland to enlarge, leads to male-pattern hair loss and, at the same time, spurs hair growth in almost every other part of the body.

Because of DHT’s effect on the prostate gland, blocking the formation of DHT with the use of finasteride can help shrink the prostate. This is not an immediate effect and may take up to six months to cause substantial shrinkage. Similarly, finasteride is a good treatment for prostate cancer because it inhibits the stimulation of these cancers. For those who have hair loss, like myself, finasteride (at a lower dose) is used to block the male pattern hair baldness caused by DHT.

As you mentioned, one side effect of inhibiting DHT is erectile dysfunction. DHT appears to play a significant role in erection as seen from multiple animal studies, and the use of finasteride and its sister drug, dutasteride, have shown erectile dysfunction in rats. In studies in men, the rate of erectile dysfunction ranged from 7.7 to 15.8 percent. This is twice the rate than that seen with placebo.

Additionally, finasteride and dutasteride’s inhibition of the enzyme 5-alpha-reductase leads to a decrease in other hormonally active chemicals. This may be the reason why some finasteride users show a decrease in libido. In studies, the number of patients reporting a loss of libido with finasteride ranged from 3.1 to 10 percent. This rate is less than two times of that seen with placebo. Lastly, finasteride has been linked to a small increase in the rate of ejaculatory problems, depression and anxiety. While the medication decreases the overall rate of low-grade prostate cancers, it has been linked to increased rate of high-grade prostate cancers.

There are other medications that decrease the symptoms of an enlarged prostate. Alpha-1 adrenergic blockers like tamsulosin, alfuzosin, terazosin and doxazosin are the first-line medications given for an enlarged prostate. They have a more immediate effect, unlike finasteride, which takes months to work, and they have been shown to improve symptoms better than finasteride.

These drugs are not without their side effects. They can lead to orthostatic hypotension, where the blood pressure drops significantly with standing, leading to lightheadedness and possibly passing out when standing quickly. Like finasteride, the alpha-1 blockers can lead to problems with ejaculation, but at a much higher rate (8 to 18 percent of men will have this as a side effect). A daily 5-milligram dose of Cialis has been shown to improve symptoms with an enlarged prostate, and this also may help erectile dysfunction.

If your husband is having problems with erections with finasteride, he should ask his doctor about alternatives.

Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.

Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.