Understandably, few side effects cause as much concern amongst finasteride users as those related to sexual function. 

In Merck’s package insert for Propecia (1 mg finasteride), their full statement reporting sexual side effects during clinical trials reads:

“A small number of men experienced certain sexual side effects.  These men reported one or more of the following: less desire for sex; difficulty in achieving an erection; and, a decrease in the amount of semen.  Each of these side effects occurred in less than 2% of men.  These side effects went away in men who stopped taking Propecia.  They also disappeared in most men who continued taking Propecia.”

Merck was a bit on the crafty side in describing the sexual side effects due to finasteride in this way.  They say that “each of these side effects occurred in less than 2% of men” and this “less than 2%” has really caught on.  It’s all most doctors will quote when they prescribe you finasteride for hair loss.  And frankly its all most of them know about sexual side effects related to finasteride.   

It’s worth a closer look at these numbers to find the true incidence of sexual side effects in men taking finasteride.

Let’s start with sexual side effects seen during the clinical trials Merck is quoting in their package insert.  And remember this is a large study with all of the appropriate controls (945 men in the finasteride group and 934 men in the placebo group).  These are good numbers!  They summarize the total sexual side effects experienced for us in a table here:

sexual side effects finasteride

So, indeed, the clinical trials showed less than 2% occurrence of each type of sexual side effect studied.  But what Merck is reporting is the incidence of different types of side effects, not the total incidence of any type of sexual side effect!

So 1.8% of men had decreased libido, 1.3% of men experienced erectile dysfunction, 1.2% with an ejaculation disorder and 1.2% with discontinuation due to a ‘sexual adverse experience’.  Add them all up and you actually have 5.5%.  Much more than “less than 2%”!

Now it turns out that some of the men in the studied experienced more than one side effect (e.g. the same person that experienced decreased libido also experienced erectile dysfunction and so on) so the actual incidence of any type of sexual side effect was 3.8% (36 of the 945 men in the study).  So 3.8% is the real incidence of sexual side effects occurring with finasteride users in this study.

Are the Numbers in these Clinical Trials Accurate?

So while Merck is (not so clearly) reporting a sexual side effect rate of 3.8%, internet forums and blogs seem to claim a much higher rate.  And in fact, some physicians that prescribe the drug, including me, anecdotally feel that the true incidence may be a bit higher than the reported 3.8%. 

The question is how much higher.  Because just thinking, “Wow, it sure seems like more than 3.8% of my finasteride patients are having sexual side effects”, is very different from going out and studying the question and getting a good, hard(??!!) number.

To get a good sense of realistic numbers, I like to point patients to one broad review of 73 papers on medical therapies for benign prostatic hypertrophy (BPH; the condition that finasteride was originally developed to treat)1.  This paper reports a range of side effect rates that obviously depend on the study, but gives you a good feel for what you might expect in terms of the likelihood of sexual side effects. 

This paper reports that problems with ejaculation in finasteride users are reported in 2.1-7.7% of patients depending on the study, erection problems are reported in 4.9-15.8%, and problems with libido in 3.1-5.4%.

These ranges seem to correlate with my experience working with patients who have been prescribed finasteride.  Some days it can feel as high as 15.8% while others the 3-5% sounds more reasonable.  I’ve taken to telling patients that as many as one in 15 to 20 can have sexual side effects with finasteride.

So Is Finasteride Not Worth the Risk Then?

When my patients hear that they have a one in 15 to 20 chance of having a sexual side effect with finasteride, a lot of them say, “No thanks, I’d rather have sexual function than my hair”.  And while I understand this initial response, there is a lot more to the story.  Let me tell you why, despite this number, finasteride is still a great solution for millions of men experiencing hair loss.

Let’s go back to Merck’s original statement where, after reporting their <2% numbers, they say: “These side effects went away in men who stopped taking Propecia.  They also disappeared in most men who continued taking Propecia.”

This statement from Merck has been true in my experience and been found in just about every finasteride study that has investigated this question.  Side effects almost always resolve in men who stop taking finasteride, and they even resolve in men who keep taking finasteride and just “power through” the side effects they initially experience.

Side Effects “Disappearing” in Men Who Continue to Take Finasteride

Let’s start with side effects disappearing “in most men who continued taking Propecia”.  To give some numbers to back up this statement, we can first look at the 3.8% of the 945 men that experienced one of the four types of sexual side effects listed in Table 1 above (1.8% or less for each type of side effect).  For patients who continued to take the drug, by the fifth year the incidence of each of the side effects was 0.3% or less (we don’t have a cumulative percent at year 5).

To add more weight to this concept of side effect reduction with increased duration of therapy, we can look at a study of patients taking 5 mg finasteride called the PLESS study (Proscar Long-term Efficacy and Safety Study).  

The PLESS study had men taking 5 mg finasteride for 4 years.  In Table 2 below you can find the incidence of four sexual side effects they examined (impotence, decreased libido, decreased volume of ejaculate, and ejaculation disorder).

sexual side effects finasteride

You’ll first notice that the incidence of all of these sexual side effects is higher than what is seen in Table 1 and that is because these men were taking 5 mg of finasteride daily instead of the 1 mg of finasteride the men in Table 1 were taking.  So the first take home point is that the rate of sexual side effects with finasteride appears to be dose-dependent.

Second, notice the difference between the rate of men who experienced one of these four sexual side in the first year versus those who experienced one of these side effects in years 2-4.  The incidence decreases with time!  Once again supporting the 1 mg finasteride study results that men who continue to take finasteride notice that a lot of the sexual side effects “disappear” with continued use.

Side Effects Going Away In Men Who Stop Taking Finasteride

The studies we have addressed also found that all men who stopped taking finasteride had any sexual dysfunction resolve.  This has been seen across thousands and thousands of patients in reported literature. 

However, an article in the Journal of Sexual Medicine reported on 71 men who experienced sexual side effects associated with finasteride that persisted for more than 3 months after cessation of the medications2.  This is a very small study with great risk for selection and recall bias, but it should not be discounted. 

It does, however, present one important issue with sexual side effects that needs to be considered.  Remember the original clinical trial we discussed where 3.8% of the 945 men had sexual side effects?  Well, the control group that was taking a placebo had a 2.1% incidence of sexual side effects during the study (20 of 934 men).

The fact is that sexual dysfunction is quite prevalent in men as they age.  The Massachusetts Male Aging Study found that complete erectile dysfunction is found in 5% of men at age 40 and 15% of men at age 70.  But more significantly, erectile dysfunction AFFECTS 40% of men at age 40 and nearly 70% of men at age 703.  In other words, while 60% of men at age 40 feel like their erections are as good as they have ever been, 40% of men at age 40 feel like they have had some degree of “erectile decline”.

It is not a surprise then, that when you put millions of men on a medication like finasteride, some will interpret the natural sexual decline experienced with aging as being secondary to finasteride treatment.

In the case of finasteride 1 mg trials it was 2.1% of men that thought their sexual dysfunction was due to the medication when in fact it was either a placebo effect or the result of aging. 

In the finasteride 5 mg trial, 3.7% of men stopped taking finasteride due to sexual side effects while 2.1% of men (exact same percentage as the 1 mg trials) stopped taking their placebo pill due to sexual side effects. 

It is also interesting to note that the rate of impotence seen in patients taking a placebo in Table 2 in the first year was 3.7% while in years 2-4 that percentage climbs to 5.1%.  Not surprisingly, the rate of erectile dysfunction increases as time goes on even if you are taking a placebo!

One of the biggest studies done on sexual dysfunction in men with male pattern baldness taking a 5-alpha reductase inhibitor looked at 17,494 men across 17 randomized control trials and found that they couldn’t even show that 5-alpha reducatase inhibitors in men with MPB certainly caused sexual dysfunction when compared with baseline rates of sexual dysfunction in the male population4.

In summary, there are men who have taken finasteride that are reporting long-term sexual dysfunction.  The number is extremely small compared to all men that have taken finasteride but, nevertheless, these people exist.  Because its such a relatively small number and because sexual dysfunction is actually relatively common in men as they age, it will be very hard for a study to ever prove for certain that finasteride can cause long-term sexual dysfunction. 

My Thoughts

While I personally have found that it seems like slightly more than 3.8% of patients have some sexual side effect while taking finasteride, for most people these effects aren’t severe enough to discontinue the medication.  (I’ve even had men tell me that the side effects were welcome because finally their libido more closely matched that of their spouse!)

Those that continue to take the medication in spite of side effects generally see the side effects disappear.  And, in my experience and that of almost all studies, those that stop the medication because they have side effects that they find concerning or intolerable have the side effects resolve completely.

All of this being said, like any medication, in the end it’s up to the patient to decide whether to take the medication.  However, this should not be done after succumbing to hysteria in an internet chat room but instead, after careful review of pertinent medical literature and thoughtful consultation with your prescribing physician.

Ultimately, the overwhelming majority of patients who take finasteride do so without side effects and with good results in hair growth and retention. 

 

1.    Carbone DJ Jr, Hodges S.  Medical therapy for benign prostatic hyperplasia: sexual dysfunction and impact on quality of life.  Int J Impot Res. 2003 Aug;15(4):299-306.

2.    Irwig MS, Kolukula S. Persistent sexual side effects of finasteride for male pattern hair loss. J Sex Med. 2011;8:1747–53.

3.    Feldman HA, Goldstein I, Hatzichristou DG, Krane RJ, McKinlay JB. Impotence and its medical and psychosocial correlates: Results of the Massachusetts Male Aging Study. J Urol 1994; 151:54–61.

4.    Liu L, Zhao S et al.  Effect of 5α-Reductase Inhibitors on Sexual Function: A Meta-Analysis and Systematic Review of Randomized Controlled Trials. J Sex Med. 2016 Sep;13(9):1297-1310.