The main ingredient of both drugs is finasteride. Finasteride reduces male hormone activity. A dose of Proscar, used to reduce symptoms of enlarged prostate (benign prostatic hyperplasia or BPH), has five times more finasteride than a dose of Propecia, used to reduce male pattern hair loss.
Both drugs are known to cause erectile dysfunction in some men. The drugs’ labels already carry this warning.
Now labels on both drugs will include new warnings:
Propecia may cause loss of sexual desire, inability to ejaculate, and inability to reach orgasm. These sexual dysfunctions may continue for some time after men stop using the baldness drug.
Proscar may cause loss of sexual desire. This may continue for some time after men stop using the drug.
Both Propecia and Proscar may cause male infertility and/or poor semen quality. This side effect lessens or goes away after men stop taking the drugs.
Propecia, Proscar Sexual Side Effects Rare
There’s no definitive proof that either Propecia or Proscar actually causes these problems. But the FDA has received enough reports of these side effects to cause concern.
Even if the drugs do cause these sexual side effects, they’ve been reported in only a small number of men. For example, in Propecia clinical trials, 3.8% of men taking the drug and 2.1% of men getting an inactive placebo reported sexual problems.
Moreover, the warnings are based on relatively small numbers of reported problems.
For Propecia, the FDA reviewed 421 reports of sexual dysfunction between 1998 and 2011. Of these, 59 cases reported sexual dysfunction that lasted for at least three months after patients stopped using the drug.
For Proscar, the FDA reviewed 131 cases of erectile dysfunction and 68 cases of decreased libido between 1992 and 2010. Reported events of erectile dysfunction and decreased libido lasted for at least several weeks after men stopped taking the drug.
The FDA identified 251 cases of poor semen quality linked to Propecia and 29 cases linked to Proscar use. Interestingly, only three of the Proscar-linked cases were in men with BPH.
Patients taking either Propecia or Proscar should talk with their doctors if they are worried about the new warnings. Men suffering sexual dysfunction or having fertility problems should consult their doctors and report the side effects to the FDA MedWatch program either online or at 800-332-1088.
Proscar and Propecia are both brand-name drugs from Merck. Generic versions of both drugs are available.
By Daniel J. DeNoon
WebMD Health News Reviewed by Laura J. Martin, MD