A new study of men taking the active ingredient in Propecia reports that some experienced erectile dysfunction that did not get better with discontinued treatment.

The study was published online in the journal Hormone Molecular Biology and Clinical Investigation. Researchers looked at the effects of finasteride, the drug used in Propecia, in 470 men who were taking it as a treatment for benign prostatic hypertrophy. They compared those men’s experiences with results from 230 men who took the drug tamsulosin for the same condition.

The researchers reported that the men who took finasteride had a “marked and significant” reduction in erectile function. They also registered a significant reduction in testosterone levels.

Prior to this study, some researchers had believed that sexual dysfunction associated with finasteride would tend to resolve with continuing treatment. However, Dr. Abdulmaged M. Traish, a corresponding author of the study, noted that these adverse sexual side effects were persistent in some cases.

He said that finasteride’s effect on sexual function is a serious concern and that physicians should be mindful of these adverse sexual side effects on their patients. Dr. Traish is a professor of biochemistry and urology at Boston University School of Medicine.

Finasteride is a drug known as a 5-alpha reductase inhibitor. This type of drug works by preventing the conversion of testosterone into dihydrotestosterone, or DHT. DHT is associated both with prostate enlargement and male pattern baldness.

Finasteride had been originally approved by the FDA in 1992 as a treatment for benign prostatic hyperplasia and sold for that purpose under the brand name Proscar. Later, researchers incidentally discovered that finasteride also could slow or stop male pattern baldness, and in 1997 the FDA approved it for that use under the brand name Propecia.

Erectile dysfunction is not the only possible sexual side effect of Propecia. In April 2012, the FDA announced changes to the labeling for both Propecia and Proscar to better reflect the different sexual side effects associated with finasteride.

After the update, the label for Propecia noted that sexual side effects include “libido disorders, ejaculation disorders, and orgasm disorders that continued after discontinuation of the drug.” The label also included mention of reports of infertility and poor semen quality that did improve following discontinuation of Propecia.

In its announcement, the FDA said a search of its Adverse Events Reporting System database had revealed 421 reports of sexual dysfunction associated with Propecia reported from 1998 to 2011. Out of those cases, 59 reported sexual dysfunction that persisted for at least three months after discontinuation of Propecia.

Sexual side effects associated with Propecia have resulted in a considerable number of Propecia lawsuits. Since April 2012, hundreds of Propecia lawsuits have been consolidated into a multidistrict litigation in a New York federal court.

Generally, the plaintiffs allege that manufacturer Merck failed to properly warn patients about the possibility of Propecia impotence and other sexual side effects.

The Propecia MultiDistrict Litigation, or MDL, is in the U.S. District Court for the Southern District of New York, MDL No. 2331.