What are the side effects of finasteride?

As the old adage goes, you take the good with the bad. Finasteride (brand name Propecia) is the most effective drug for treating male pattern baldness, preventing hair loss in 83% of men treated for two years (Shapiro, 2003). But finasteride can cause side effects, most commonly involving sexual function. Understandably, this can cause some people considering finasteride a bit of anxiety. 

Here are a few things to think about when you're deciding whether to take finasteride for your hair loss.

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Finasteride, an oral medication known as a 5-alpha-reductase inhibitor, works by blocking the production of dihydrotestosterone (DHT). DHT is a male sex hormone that can attack hair follicles on the head and cause them to shrink. Blocking DHT can stop hair loss, but it can have unwanted effects, including (Fertig, 2017; FDA, 2012):  

• Decreased libido

• Erectile dysfunction (ED): trouble getting or keeping an erection

• Decreased semen volume

• Gynecomastia (breast enlargement) and breast tenderness

• Ejaculatory problems like premature ejaculation (PE)

Fortunately, finasteride’s side effects aren’t very common. During Propecia’s clinical trials, only 3.8% of men taking the drug experienced side effects, versus 2.1% of men taking a placebo (Mcclellan, 1999). 

Another study showed that side effects usually resolved once men stopped taking the drug. In men who continued taking the medication, the incidence of side effects declined over time, dropping to less than 0.3% in people taking finasteride for five years (Mysore, 2012).

Finally, a 2017 meta-analysis reviewed 17 studies involving nearly 18,000 men taking 5-alpha-reductase inhibitors. The study found that there wasn't a significant increase in sexual side effects in people taking the drug for hair loss. Only people taking them for enlarged prostates (which required a higher dose) experienced significant increases in sexual side effects (Fertig, 2017). 

Some men take a variation of finasteride called Proscar for a condition called benign prostatic hyperplasia (BPH). Its dose is five times higher than the dose of finasteride for hair loss, so there may be a higher risk of sexual side effects with the higher dose of finasteride. 

Sounds pretty straightforward, right? Side effects are rare, transient, and reversible, but they do happen. And "rare" is pretty meaningless if it happens to you.

What to consider before taking finasteride

A tiny decrease in semen volume may seem trivial to some men, but erectile dysfunction may not, even if it goes away with time. And in rare cases, some men have reported side effects that last after they stop finasteride. 

So, it is important to do a cost-benefit analysis when you consider taking a new medication. If you find your hair loss really bothersome, and you aren't too worried about a low risk of sexual side effects, getting a finasteride prescription might be the right choice for you. 

Conversely, if you're on the fence about your hair loss or prefer to eliminate the risk of side effects, no matter how small, you might choose to skip it. When in doubt, your healthcare provider can discuss different options available to you and answer any questions you may have.

Something that is of significance to note when weighing the pros and cons of finasteride is that once DHT has caused a follicle to "die," it's difficult to revive it. The sooner you take action, the more likely you'll be successful at reversing baldness and regrowing some hair.

 Other possible side effects of finasteride are less common, but include:

• Allergic reactions, including rash, itching, hives, and swelling of the lips, tongue, throat, and face

• Testicular pain

• Male infertility and/or poor semen quality 

• Persistent ED, PE, or low sex drive after discontinuing the drug

• In rare cases, male breast cancer has occurred. Tell your healthcare provider if you have any breast lumps or nipple discharge. 

• Finasteride can affect a blood test called PSA (prostate-specific antigen), which is used to screen for prostate cancer. If you have a PSA test done, tell your healthcare provider you're taking finasteride; they'll need to take that into account when they evaluate your PSA levels (Etzioni, 2005). 

• Depression and suicidal thoughts

These are not all the possible side effects of finasteride. For more information, speak to your healthcare provider or pharmacist.

It’s not always possible to avoid side effects, but you can take steps to reduce the likelihood. 

For example, always take the medication as prescribed by your healthcare provider. Don’t skip doses or take extra doses. Take your prescribed medications consistently as directed. Discuss any side effects with your provider, as some may be temporary and resolve with time.

The U.S. Food and Drug Administration (FDA) tested many drugs to look for interactions with finasteride. No significant drug interactions were seen, but always let a healthcare professional know about any medications you are taking before starting finasteride (FDA, 2021).  

People with liver problems should consult with a healthcare professional before starting finasteride. 

Finasteride should not be given to children, and people who are pregnant or may become pregnant should not take finasteride or handle broken or crushed finasteride tablets. The active ingredient may be absorbed by the skin and harm fetuses (FDA, 2021). 

Side effects can happen when you take finasteride, but their incidence is very low. Be sure to balance the potential benefits with any possible risk before taking a new medication. Your healthcare provider can help you learn more about possible side effects from finasteride.  

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Current version

December 13, 2021

Written by

Michael Martin

Fact checked by

Felix Gussone, MD

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About the medical reviewer

Felix Gussone, MD, Ro

Felix Gussone is a physician, health journalist and a Manager, Medical Content & Education at Ro.