Finasteride is one of only two clinically proven and licensed treatments for male pattern baldness in the UK (alongside Minoxidil Spray), which means it has been thoroughly tested and deemed both safe and effective at 1mg dosage to treat hair loss. Finasteride, like any medication, is continually assessed through a risk–benefit process by licensing authorities to ensure its benefits outweigh any potential risks. As more data become available from ongoing studies and real-world use, this balance is regularly reviewed.
In this article, we’ll look at clinical studies examining the sexual side effects of oral Finasteride - so you can see what the risks are, how often they occur, and decide if this treatment suits you.
What is Finasteride and how does it work for hair loss?
Finasteride is licensed by the MHRA (the agency responsible for regulating medicine in the UK) at 1mg for the treatment of androgenetic alopecia (male pattern baldness). It is also prescribed at a higher dosage of 5mg to treat benign prostate hyperplasia (BPH), aka enlarged prostate. During clinical trials for Finasteride as a treatment for BPH, researchers noticed it seemed to stimulate hair growth, leading to its approval for treating hair loss in 1999.
Finasteride helps prevent hair loss by blocking dihydrotestosterone (DHT), the main hormone responsible for male pattern baldness. It works by inhibiting the enzyme 5α-reductase, which converts testosterone into DHT. By lowering DHT levels, Finasteride has been shown in countless clinical trials to slow or reverse hair loss in men.
However, like many medications, Finasteride only works while you continue taking it - if treatment stops, hair loss will gradually resume. Because it’s often used long term, especially by younger men with early hair loss, it’s natural to wonder about its long-term safety. Many men are particularly concerned about possible sexual side effects, which we’ll explore in more detail below.
How does Finasteride impact DHT and testosterone levels?
A review of the available research explains that as testosterone directly influences male libido, people often assume any drug affecting male hormones will impact sexual function. However, Finasteride works by lowering DHT levels, not testosterone itself. In fact, some studies show Finasteride may lead to a slight increase in testosterone levels, although not in everybody. DHT plays a smaller role in adult sexual function. It is important during male puberty for the development of secondary sexual characteristics (think: deep voice and facial hair). In adulthood, DHT is mainly responsible for growing the prostate gland and body hair (and of course, male pattern baldness).
Even so, concerns about sexual side effects are understandable. So, what does the evidence show about how common they are?
What are the risks of sexual side effects?
Many studies have investigated whether Finasteride is linked to sexual side effects, such as erectile dysfunction, reduced libido, or changes in semen quality. To date, no consistent causal relationship has been established between 5α-reductase inhibitors (like Finasteride) and persistent sexual symptoms.
A large review combining data from multiple clinical trials report that sexual side effects occur at a rate of 2.1% to 3.8%. The most frequently reported issue is erectile dysfunction, followed by ejaculatory dysfunction and loss of libido. These typically occurred early in therapy or resolved upon stopping the medication or with continued use.
A study published in The Journal of Sexual Medicine specifically investigated the ‘nocebo phenomenon’ - when side effects arise from the psychological awareness of the possibility of side effects, rather than as a direct result of the specific pharmacological action of the drug. In the trial, half of the men were told Finasteride might cause sexual side effects, while the other half were not. Among those warned, 43.6% reported sexual symptoms, compared with only 15.3% in the group that were not told. This finding highlights the powerful role that awareness and anxiety can play in how side effects are perceived. The researchers of this study suggested that the nocebo effect should be considered by prescribers when managing Finasteride sexual side effects.
Another significant study published in The British Medical Journal looked at more than 70,000 men using 5α-reductase inhibitors (Finasteride or Dutasteride) to treat BPH and found no increased risk of erectile dysfunction compared with men treated with α-blockers.
The researchers also evaluated a second group of 12,346 ‘real-world’ men using 1mg Finasteride daily for alopecia. Again, the men using Finasteride were no more likely to develop erectile dysfunction than men with alopecia who didn’t take it. For other sexual side effects, the rates were very low in both users and non-users. The rate of ejaculatory disorder was 0.3 per 1000 users for users of Finasteride, compared to 0.8 per 1000 in non-Finasteride users, while the incidence rate of low libido was 0.8 per 1000 in both groups.
A long-term, 5-year study involving 1,215 men taking 1mg Finasteride found sexual side effects in less than 2% of participants. These symptoms disappeared in all men who discontinued use, and in most who continued with the medication. By the fifth year of treatment, the reported rate dropped to ≤0.3%, comparable to the rate in the placebo group.
The International Society of Hair Restoration Surgery (ISHRS) put together a task force on Finasteride Adverse Event Controversies, who concluded:
“The persistence of sexual side effects appears to be a rare event, and it has yet to be determined whether these recent reports represent a true causal relationship, or if they are simply coincidental and related to other factors such as the high incidence of sexual dysfunction in the general population, and/or the placebo effect.”
Among all reported effects, the only consistent causal relationship between Finasteride and sexual symptoms is a reduced ejaculatory volume, because of the role DHT plays in the size of the prostate. An older study found that Finasteride does not significantly affect sperm concentration, motility, or morphology. Later research noted mild, reversible reductions in sperm count and semen volume, but these remained within normal fertility ranges and returned to baseline after discontinuation.
Are there any alternatives if you do experience side effects?
Finasteride is also available as a topical spray, which has been shown in studies to be similarly effective to oral Finasteride, but with a lower risk of side effects. The difference comes down to how the medication is absorbed: when applied directly to the scalp, it acts locally on the hair follicles, with only a small amount entering the bloodstream. Because less Finasteride circulates in the body, the spray has less impact on serum DHT levels (the DHT found in the bloodstream) while still effectively lowering DHT levels in the scalp, where it matters most for hair loss.
For this reason, many men choose Finasteride spray if they’re concerned about side effects from the oral form or have experienced them in the past.
On Finasteride and potential sexual side effects, Sons Medical Director Dr. Knut Moe says: “Finasteride has been licensed for use in male pattern hair loss since the 1990s and as a result, is very well studied. There has been extensive research on side effect and safety surrounding sexual side effects, which a recent study published in the British Medical Journal finding that there was no stattically significant increase in erectile dysfunction in those taking Finasteride versus placebo. Nevertheless, anyone looking to take Finasteride should familiarise themselves with the potential side effects before they take it, if deemed suitable based on their medical history.
If you’re interested in hair loss treatment but unsure where to start, take our online consultation for personalised treatment recommendations based on your stage of hair loss and preferences.
All of our blog articles are reviewed by our Medical Director before publication.
