The medications include Propecia (1-mg finasteride), Proscar (5-mg finasteride), and Avodart (dutasteride). They prevent the conversion of testosterone into its more-powerful form dihydrotestosterone (DHT).
This is an effective way to treat male-pattern baldness, but it also creates a hormonal imbalance in the male body. In clinical trials, 3.8% of men on Propecia reported at least one symptom of sexual dysfunction.
The problem is that hormone levels may not return to normal when the medications are discontinued. According to the study’s lead author Dr. Steven Belknap:
Men can get persistent erectile dysfunction, in which they will not be able to have normal erections for months or years after stopping finasteride or dutasteride.”
The study found that 167 out of 11,909 men (1.4%) developed erectile dysfunction that continued for a median of 1,348 days after discontinuing the medication.
Men under 42 years old who used the medications for more than 205 days were 4.9-times more likely to develop persistent erectile dysfunction compared to men who used the medications for less time.
The study was published March 9 in the journal PeerJ by researchers at Northwestern University.
Around 1,000 lawsuits have been filed by men who accuse Merck & Co. of downplaying the risk. Warnings about “persistent erectile dysfunction” were not added to the label on Propecia or Proscar until 2011.
The FDA expanded the list of possible side effects to include cancer, libido disorders, ejaculation disorders, and orgasm disorders that continued after discontinuation of the drug. The label has also been updated to include reports of depression.