Finasteride AKA Propecia. Does it cause erectile dysfunction?

All medications have side effects.  Many medications may cause erectile dysfunction as a side effect.  Propecia is one of the drugs that may cause ED as a side effect in 1 to 2% of men who take it. Please discuss all concerns with your doctor before starting any medication.

Hello in Toronto,
Thank you for posting. I'm going to give you the long version of the answer:
Finasteride is the most effective, approved medical treatment for androgenetic (male pattern) hair loss.  It works by blocking the conversion of Testosterone to Dihydrotestosterone (DHT) in your hair follicles by an enzyme called 5-alpha-Reductase.  It is DHT that has an adverse effect on hair, causing progressive thinning, miniaturization and baldness.  Blocking the production of DHT within the hair follicles using Finasteride has been shown in several scientific studies to slow down the rate of hair loss, accelerate growth and produce thicker and darker hair.

Finasteride is very safe for adult men to take orally. It is available as a 1mg tablet (Propecia), and as a 5mg tablet (Proscar), but the 1mg per day is sufficient to obtain essentially all the benefits.  

There are potential side effects to ANY medication, including Finasteride.  There are risks of allergy, nausea, aches and pains, headaches, swelling, but these are common to ALL medications. The main ones everyone has been talking about on the internet are decrease in sexual desire, difficulty achieving orgasm, difficulty maintaining an erection and reduced sperm count.  When these side effects were studied properly, it was found that fewer than 4% of patients that use Finasteride and no other medication, reported these side effects.  However, and this is very important, between 2-3% of men taking a placebo (sugar pill) also reported the same symptoms, so the true rate caused by Finasteride is much lower than 4%.  That's a very small rate of side effects, and the studies also found that in more than 50% of those patients the side effects went away after a few weeks even if  the patients continued to take the pill!  In the 50% of patients where the effects didn't go away, stopping the medication also stopped the side effects.  So in actual fact, the true rate of side effects on sexual function is very, very low, the effects go away on their own, but occasionally, a very small number of patients choose to the stop the medication and get better.

Finasteride can interfere with a common test we do for prostate enlargement/cancer.  If you take Finsateride and your are over 45 years old and get regular screening tests for prostate cancer, you simply need to tell your doctor and they can make adjustments to the test results.

There are many myths about propecia. Regarding erectile dysfunction, the rate of problems is related to the dose. At 1mg oral daily, the rate of ED is 3-4%.  If you give someone a placebo, the rate of ED is 2-3%. The relative risk is thus 1-2%.  If you get a reduction in libido, it tends to show up at 3 weeks and may go away at 6 weeks when your brain adjusts to the new DHT levels floating around in your blood. When you stop propecia, your DHT rises and your libido should return. Ultimately, your physician should guide you - but, the risk is pretty low. Hope this helps.