Hair loss drugs linked with erectile dysfunction

"Men who take this drug [finasteride] to combat baldness are 'five times more likely to suffer erectile dysfunction'," The Sun reports.

While this may sound hair-raising, the actual evidence the paper is reporting on is not a major cause for concern.

This US study looked at a medical records database to see how common erectile dysfunction (impotence) was among men prescribed two drugs, dutasteride and finasteride, both used to treat non-cancerous prostate enlargement. The drugs work by blocking the male hormone testosterone. A low dose of finasteride is also used to treat male pattern baldness.

Overall they found that around 1 in 17 of all men prescribed either drug for prostate enlargement had erectile dysfunction. This figure fell to 1 in 31 of those prescribed finasteride for baldness. Using the drug for longer was generally linked with a higher risk. However, in 99% of men, stopping the drugs solved the problem so it wasn't as catastrophic as the media implies.

The research highlights a known side effect of these drugs but shouldn't give too much cause for concern. If sexual problems do occur, the drug can be stopped, solving the problem in nearly all cases.

Where did the story come from?

The study was carried out by researchers from Northwestern University, Chicago, and the University of Catania in Italy. It was funded by grants from the National Institutes of Health. Additional funding was provided from the Post-Finasteride Syndrome Foundation.

The study was published in the peer-reviewed journal PeerJ on an open-access basis so you can read or download the study for free (PDF, 2.04Mb).

The Sun and the Mail Online are arguably guilty of exaggerating the results. While their reports of the increased risk of erectile dysfunction are largely accurate, they don't make clear that the actual risk of persistent problems once you stop the drugs is extremely small.

Also the Mail's claim that "Viagra doesn't help" is unsupported. The study only looked at whether Viagra (sildenafil) was prescribed, not whether it worked or not.

What kind of research was this?

This was a cohort study that aimed to investigate whether length of time taking a class of drugs known as 5a-reductase inhibitors (5α-RIs) increased risk of erectile dysfunction.

There are two 5α-RI drugs – finasteride and dutasteride – both of which effectively inhibit the male hormone testosterone by blocking the enzyme involved in its metabolism. Both are licensed to treat benign enlargement of the prostate gland, but a low dose of finasteride is also licensed to treat male pattern baldness. Both drugs are already known to have side effects of decreased libido (sex drive) and erectile dysfunction.

This study aimed to see whether the duration of exposure has an effect, and whether it persists after stopping the drugs.

What did the research involve?

The study included men from the Chicago region who had taken 5α-RIs.

Electronic medical records were accessed to look at the drug, dose, and duration of use. Researchers searched the database for recorded side effects of impotence or erectile dysfunction.

This was defined as the first recorded instance, which coincided with discontinuation of the 5α-RI and prescription of a phosphodiesterase -5 inhibitors (PDE5I), such as sildenafil to treat the problem.

They also looked at recorded diagnoses such as prostate disease, prostate cancer and alopecia, along with other medical conditions such as cardiovascular disease, high blood pressure, diabetes or obesity, to analyse the influence of these factors.

Researchers analysed the effect of low-dose finasteride (<1.25mg – taken for male pattern baldness) vs. higher dose (5mg – taken for prostate enlargement), and also finasteride vs. dutasteride. They also included a comparison cohort of men prescribed 5α-RIs and with no record of erectile dysfunction, and men who had not taken 5α-RIs.

What were the basic results?

The database included 691,268 men and 17,475 had 5α-RI exposure.

Men who had taken 5α-RIs were more likely than non-exposed men to have had a recording of erectile dysfunction in their medical records, with on average one case for every 17 men prescribed the drugs. They were also more likely to have recordings of low libido and to have been prescribed a PDE5I.

Erectile dysfunction was linked with exposure duration above 90 days. 1.4% of men also had persistent erectile dysfunction that lasted for 90 days after discontinuing the drugs.

Young men (age 16 to 42) prescribed low-dose finasteride (<1.25mg) were also more likely to have a record of erectile dysfunction recorded with 31 cases for each man prescribed the drug. Of young men on low dose, 0.8% had erectile dysfunction that persisted after stopping the drugs.

Other factors that were strong predictors of erectile dysfunction, aside from use of 5α-RIs, were records of prostate disease or prostate surgery, a greater number of medical consultations and increased age.

The four strongest predictors for erectile dysfunction that persisted after stopping 5α-RIs were prostate disease, increased age, duration of use and prescription of anti-inflammatory drugs alongside 5a-RIs.

Specifically in young men taking low-dose finasteride the strongest factor for risk of persistent erectile dysfunction was duration of use, with use above 205 days linked to increased risk.

How did the researchers interpret the results?

The researchers conclude: "Risk of persistent erectile dysfunction was higher in men with longer exposure to 5α-RIs. Among young men, longer exposure to finasteride posed a greater risk of PED [permanent erectile dysfunction] than all other assessed risk factors."


This review confirms what is already known, that 5α-reductase inhibitors (5α-RIs) increase risk of erectile dysfunction.

However, it also shows that even the low-dose formulation of finasteride taken by younger men for male pattern baldness is associated with increased risk.

It is important to recognise that erectile dysfunction is already a known risk of the drug. It occurred in around one in 31 young men exposed – but the vast majority of cases resolved after stopping the drug. Erectile dysfunction only persisted in less than one in 100 young men after discontinuation of 5α-RI treatment.

Even for men taking the standard higher dose for enlarged prostate, only 1.4% had persistent erectile problems after stopping the drug.

Therefore it is a slight media distortion to suggest that this is a permanent problem and "Viagra won't help". The researchers looked for prescription of drugs such as Viagra to indicate the problem in the medical records, but they haven't looked at response to this at all.

Another limitation is that this study looked at medical records from one region of the US only. This may not give a true representation of how common erectile dysfunction is among men prescribed these drugs – either for enlarged prostate or male pattern baldness. Some men may not have discussed adverse sexual effects with their doctor and it may not have been documented in the medical records.

Overall, the research highlights a known side effect of these drugs but does not give overt cause for concern. Men prescribed these drugs for male pattern baldness will have been informed of the side effects. If sexual problems do occur, the drug can be stopped and the problem will resolve in nearly all cases.   

NHS Attribution