A review of 34 clinical trials on a popular drug to treat hair loss in men found that none of the studies adequately reported on sexual side effects, researchers said Wednesday.

The findings raise serious questions about whether the drug -- known as finasteride and marketed as Propecia and Proscar, among other names -- is safe, said the report by scientists at Northwestern University, published in the Journal of the American Medical Association (JAMA) Dermatology.

The drug, approved in 1992, works by interfering with testosterone, and the pharmaceutical giant Merck lists decreased sex drive, impotence and problems with ejaculation among its common side effects.