FDA Warns of Sexual Side Effects with Finasteride (Propecia & Proscar)

by on April 15, 2012

The FDA has directed Merck to place additional warnings of potential sexual side effects on the labels of Propecia, which treats male pattern baldness, and Proscar, which treats symptoms of benign prostatic hyperplasia (BPH), or enlarged prostate. Both drugs contain Finasteride which inhibits some male hormonal activity.

Adverse Events Reporting System

The FDA has a system whereby health professionals and private individuals can voluntarily report adverse events believed to be related to an FDA approved drug. The Adverse Events Reporting System (AERS) received 421 reports of sexual dysfunction between 1998 and 2011, connected to the use of Propecia. From 1992 to 2010, 131 cases of erectile dysfunction and decreased sex drive were reported connected to the use of Proscar. No studies were done to confirm these reports, and the symptoms reported could have other causes.

Product Label Changes

Because of the events reported to AERS, the FDA has directed Merck to modify the warning labels on Propecia and Proscar. In 2011 warnings were added to both labels about erectile dysfunction and the possibility of a higher risk of prostate cancer. Now the warnings are being expanded to include decreased libido for Proscar, and ejaculation/orgasm disorders for Propecia accompanied by a note on both that these symptoms might last even if the drug is discontinued.


Testosterone is the common denominator in male hair growth and prostate glands. A male androgen, or sex hormone, testosterone is converted to dihydrotestosterone (DHT) in the body by the 5-alpha reductase enzyme. It is the DHT that is troublesome. Early in life, DHT is important in the growth and development of the male fetus, and child. But later in life, DHT causes hair follicles to dry up and prostate glands to enlarge. The goal of Propecia and Proscar is to slow down the 5-alpha reductase enzyme, thereby reducing the production of DHT.

The Finasteride Connection

It seems logical that any tampering with male hormones could have side effects that result in changes to sexual functions. DHT has been proven to cause male pattern baldness and enlarged prostate glands, so less DHT should improve things. Finasteride, the main ingredient in Propecia and Proscar, interferes with the production of DHT. In spite of the label changes and increased warnings, the FDA says that there have never been established connections between sexual dysfunction and Finasteride.


Minoxidil marketed as Rogaine (Upjohn) contains Finasteride, and was originally used to treat high blood pressure, but exhibited the side effect of increased hair growth. Another FDA approved product Avodart (GlaxoSmithKline) that inhibits the 5-alpha reduction enzyme contains dutasteride. This drug has been approved for treatment of BPH but not for baldness. Procerin, touted as being a supplement and available without a prescription, claims to block the production of DHT using saw palmetto berries, zinc, pyroxidine, and a proprietary blend of herbs and vitamins.

In spite of the FDA’s approval of many products that impact the production of male and female hormones in the human body, many functions of hormones are unknown. Drugs that have passed clinical trials and appear to be safe can still cause side effects that researchers have not yet encountered. By updating the warning labels throughout the life of a drug, the FDA is communicates safety concerns as they arise.

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