Reduced ejaculation and semen volume and depression were also reported by some men, the researchers note.
Traish said doctors need to inform their patients about the potential side effects.
"As a physician you have a responsibility to take the time and explain to your patient that maybe not everyone will have these side effects, but you may, and in some cases they are irreversible," he said.
He also said alternative medications are available to treat BPH, including alpha-blockers such as Flomax, which work differently in the body. Often these are given in combination with Propecia or Avodart.
Commenting on the study, Dr. Bruce R. Kava, an associate professor of urology at the University of Miami Miller School of Medicine, agreed that "these drugs do cause some of these problems."
That the effects might not be reversible is a concern, he said. "But they haven't convinced me yet, based on this data, because they don't have any long-term data," Kava said.
Most urologists discuss potential side effects with their patients, Kava said. "We don't usually discuss long-term consequences that are irreversible, because most of us have not been aware of any long-term problems from these drugs," he said.
For more information on erectile dysfunction, visit the U.S. National Library of Medicine.
SOURCES: Abdulmaged M. Traish, Ph.D., professor, biochemistry and urology, Boston University School of Medicine; Bruce R. Kava, M.D., associate professor, urology, University of Miami Miller School of Medicine, March 2011 Journal of Sexual Medicine
All rights reserved