Propecia Breast Cancer Side Effects in Men Leads to New Warning in Canada

Canadian health officials have issued a new warning about the risk of male breast cancer from side effects of Propecia and Proscar, which are used to treat male pattern hair loss and enlarged prostates. 

On August 4, Health Canada announced the new label warnings for drugs that use finasteride as an active ingredient, indicating that there have been reports of male breast cancer from a small number of patients worldwide who were taking Propecia or Proscar.

Health Canada states that there is not enough evidence yet to definitively link the drugs to breast cancer, but does recommend that patients taking Propecia or Proscar report any changes in their breasts to their doctor. Those changes could include breast enlargement, lumps, tenderness, pain or nipple discharge. The warnings only apply in Canada, and do not affect the U.S. labels for the Merck & Co. drugs.

Proscar (finasteride) was approved in 1992 for the treatment of benign prostatic hyperplasia and comes in 5 mg doses. Propecia is a 1 mg dose version of Proscar that is approved to treat male pattern baldness.

The Canadian warning comes after the FDA issued a prostate cancer warning for Propecia and Proscar in June. The drugs belong to a class of medications known as 5-alpha-reductase inhibitors. They reduce hair loss and can shrink an enlarged prostate by blocking a hormone known as dihydrotestosterone (DHT).

In March, researchers from the U.S. published a study in the Journal of Sexual Medicine that found side effects of Propecia and similar drugs were linked to sexual problems in men. Researchers indicated that 5-alpha-reductase inhibitors can cause loss of libido, depression erectile dysfunction, reduced semen production and growth of male breast tissue. They also agreed that in some cases these side effects appeared to be permanent.