Finasteride Side Effects: What Actually Happens and What the Evidence Says

Few pills cause as much fear as finasteride. Online there are forums describing permanent impotence and depression, and at the same time dermatologists who prescribe it every day as one of the best-studied treatments for hair loss.

This guide sorts out what is actually known: how often side effects occur in serious studies, who should not take it, and what role it plays if you are considering a hair transplant. It is not a prescription; it is what we would explain to you in a consultation.

Quick answer

• Finasteride works. In clinical trials, 1 mg a day slowed hair loss and increased hair counts versus placebo over five years of follow-up.
• Sexual side effects are real but uncommon: in controlled trials, roughly 1 additional case of erectile dysfunction for every 80 men treated.
• Fear produces symptoms too (the nocebo effect): warning men about sexual side effects nearly tripled how many reported them.
• Post-finasteride syndrome (symptoms that persist after stopping) has been reported and is being studied, but how common it is and what causes it are still debated.
• It lowers PSA by about half. If you are screened for prostate cancer, your doctor needs to know you take it.
• It is not for women who are or could become pregnant, and a pregnant woman should not handle broken or crushed tablets.
• Dutasteride, its close relative, performed better in head-to-head trials, with similar sexual side-effect rates. It is what we usually use at Colombia Care, after a medical review.
• It does not replace a transplant, and a transplant does not replace it. A transplant redistributes hair; finasteride protects the native hair you have not lost yet.

What finasteride does and why it works

Androgenetic alopecia, ordinary male pattern baldness at the temples and crown, happens because some follicles are sensitive to dihydrotestosterone (DHT), a hormone made from testosterone by an enzyme called 5-alpha reductase. Over the years DHT shrinks those follicles: the hair grows back finer and shorter until it stops growing at all. That progression is what the Norwood scale measures.

Finasteride blocks that enzyme (type 2) and lowers DHT. It does not grow hair where there is no follicle left: it slows miniaturization and, in some patients, recovers follicles that were weakened but still alive.

What the studies show:

• In the two pivotal trials, with 1,553 men aged 18 to 41, finasteride 1 mg a day improved scalp hair versus placebo by every measure at one and two years, while the placebo group kept losing hair (Kaufman et al., 1998).
• In the five-year extension, the improvement held, the drug was well tolerated, and no new safety concerns emerged (Finasteride Male Pattern Hair Loss Study Group, 2002).
• A systematic review of 12 trials (3,927 men) concluded, with moderate-quality evidence, that it increases hair counts and improves appearance, at the cost of an increased risk of sexual dysfunction (Mella et al., 2010).

In short: it works, and there is a price. The honest question is how big.

The side effects, one by one

Sexual side effects: the real number

The most common fear is impotence. The best synthesis of placebo-controlled trials found that finasteride does increase erectile dysfunction (relative risk 2.22), but because the baseline rate is low, the number of men who need to be treated for one to have that effect because of the drug was about 82. In the same review, the share of men who stopped treatment because of sexual side effects was similar with finasteride and with placebo (Mella et al., 2010).

Put another way: it is not an invented side effect, but it is not what happens to most men either. According to the drug's prescribing information, in most men who experience these effects they resolve after stopping; the debated exception is post-finasteride syndrome, covered below.

The nocebo effect: why fear produces symptoms too

An Italian study gave finasteride to 120 men without telling them what it was. Half were warned that it "may cause erectile dysfunction, decreased libido, problems of ejaculation but these are uncommon." The other half were told nothing. At one year, 43.6% of those warned reported at least one sexual side effect, versus 15.3% of those who were not (Mondaini et al., 2007).

One caveat: that study used the 5 mg prostate dose, five times the hair dose. But the point holds: expectation matters. The symptoms are not imaginary, they feel just as real, but part of what gets blamed on the drug comes from fear of the drug. That is why we prefer to walk through the data before you start.

Post-finasteride syndrome

Some men report sexual, mood, concentration or physical symptoms that persist after stopping finasteride: post-finasteride syndrome. A recent review describes it as a contested condition, with conflicting data in the literature, and calls for more research and a proper risk conversation before prescribing (Cilio et al., 2025).

Our reading: it is rare, poorly understood, and should not be dismissed. If you have a history of depression, significant anxiety or prior sexual dysfunction, say so before starting; it can change the recommendation.

Mood and the FDA label

In 2022 the US FDA updated the finasteride label to include suicidal ideation among the effects reported after the drug went on the market. That does not prove finasteride causes suicide, but it does call for vigilance: any change in mood, persistent sadness or thought of harming yourself is a reason to stop and see a doctor immediately, not to wait.

PSA and the prostate

PSA is the blood test used to screen for prostate cancer. In a trial of men aged 40 to 60, finasteride 1 mg lowered PSA by a median of 40% (ages 40 to 49) and 50% (ages 50 to 60) over 48 weeks. The authors concluded that the rule already used for the 5 mg dose, adjusting the value, typically by doubling it, also applies to the hair-loss dose (D'Amico & Roehrborn, 2007). If you have prostate check-ups, your urologist needs to know you take it; otherwise a "normal" PSA may not be.

Women: the warning that is absolute

Finasteride is not approved to treat hair loss in women and must not be used by women who are or may become pregnant, because it can affect the genital development of a male fetus. For the same reason, a woman who is pregnant or planning a pregnancy should not handle broken or crushed tablets. Whole tablets are coated, but if someone in your home splits pills, be careful. In some postmenopausal women it is used off-label under medical supervision; that is a specialist's decision, not self-prescription.

Alternative: topical finasteride

Topical finasteride. A spray solution applied to the scalp. In a phase III trial of 458 men, it increased hair counts versus placebo with an effect numerically similar to the pill, and adverse events did not differ from placebo. Blood concentrations were more than 100 times lower and DHT dropped less (34.5% versus 55.6% with the oral form), making a DHT-related sexual side effect less likely (Piraccini et al., 2022). For anyone wary of the pill it is a reasonable option to discuss; it is not available or approved everywhere, so ask your doctor what is available where you live.

Dutasteride: what we use at Colombia Care, and why

Finasteride is the best-known drug in its family, but it is not the only one. At Colombia Care, when a patient needs medical treatment to slow androgenetic alopecia, our usual preference is dutasteride, always after a medical review.

What makes it different. DHT is made by two enzymes: type 1 and type 2 5-alpha reductase. Finasteride blocks only type 2; dutasteride blocks both, so it lowers DHT further, in the blood and in the scalp (Olsen et al., 2006).

What the head-to-head studies show:

• In the largest trial, 917 men over 24 weeks, dutasteride 0.5 mg increased hair count and hair width more than finasteride 1 mg and more than placebo, and the number and severity of side effects were similar across groups (Gubelin Harcha et al., 2014).
• A meta-analysis of three trials (576 men) reached the same conclusion: better efficacy than finasteride, with no significant difference in libido, erectile function or ejaculation (Zhou et al., 2019).

The honest caveats. The comparison trials ran 24 weeks, so there is less long-term data than for finasteride. The precautions are the same ones covered above: it also lowers PSA, it is not for women who could become pregnant, and pregnant women should not handle the capsules. Because it stays in the body for weeks, a side effect also takes longer to fade after stopping, and you should not donate blood while taking it or for several months afterwards. That is why we only prescribe it after reviewing your case, and it is not for everyone.

How it fits with a hair transplant. The transplant puts hair where there is none; dutasteride helps protect the native hair you have not lost yet, which is exactly what decides how your result looks in five or ten years.

If you want to know whether dutasteride is an option for you, message us on WhatsApp and a physician will explain how we use it.

What all this has to do with a hair transplant

This is the most misunderstood point. A hair transplant in Medellín takes follicles from the back of the head, which are resistant to DHT, and places them where hair is missing. Those transplanted follicles keep their resistance and usually last a lifetime; that is why we talk about permanent results.

What a transplant does not do is stop hair loss in the native hair in and around the treated area. That native hair is still exposed to DHT. If it keeps falling out after the transplant, over the years you can end up with a band of transplanted hair and a gap behind it. In good candidates, finasteride protects that native hair:

That is why, in young men or men with active loss, we often recommend stabilizing first with medical treatment for a few months and planning the transplant around a more predictable pattern. Part of shock loss also affects weakened native hair. None of this is mandatory: some patients do not want to, or should not, take finasteride and are still candidates, with a more conservative hairline and donor plan.

The practical side, if your doctor prescribes it

• The approved dose for androgenetic alopecia is 1 mg a day. Taking more does not "speed things up"; the 5 mg dose is for the prostate. Any adjustment is your doctor's call.
• Be patient: results are judged at 6 to 12 months. Some temporary shedding of weak hairs can happen in the first months.
• If you stop, the effect is lost over the following months and hair loss resumes its course.
• Keep a record: photos in the same light every three months and a note of any symptom.
• Stop and consult with mood changes, sexual symptoms that worry you, breast pain or a lump.
• Always tell people you take it: your urologist, before a PSA test, and if your partner is pregnant or planning to be.

Who should think twice

• Women who are or could become pregnant (not an option).
• Men trying to conceive with their partner who want to discuss it with their doctor first.
• Men with active depression or a significant mental-health history: not an absolute bar, but it calls for a more careful conversation and follow-up.
• Anyone with sexual dysfunction that has not been evaluated: find the cause first.
• Anyone planning to take it without a prescription or medical follow-up, bought online.

Summary

Finasteride is one of the hair-loss treatments with the most years of data behind it. Sexual side effects are real, uncommon and generally resolve after stopping, and fear amplifies them. Post-finasteride syndrome and mood changes are rare, under study, and warrant vigilance. If you are considering a hair transplant, the question is not "transplant or finasteride" but how each fits into your ten-year plan. And if finasteride worries you, dutasteride is the alternative we usually recommend; ask us about it.

If you would like a physician to review your case, how active your hair loss is, whether medical treatment makes sense before or after a transplant, or whether a transplant makes sense at all, book a free assessment.

Message us on WhatsApp and a physician will reply →

This article is for information only and does not replace a medical consultation. Do not start, change or stop a medication without talking to your doctor.

Sources

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2. Finasteride Male Pattern Hair Loss Study Group. Long-term (5-year) multinational experience with finasteride 1 mg in the treatment of men with androgenetic alopecia. Eur J Dermatol. 2002. PMID 11809594
3. Mella JM, et al. Efficacy and safety of finasteride therapy for androgenetic alopecia: a systematic review. Arch Dermatol. 2010. PMID 20956649
4. Mondaini N, et al. Finasteride 5 mg and sexual side effects: how many of these are related to a nocebo phenomenon? J Sex Med. 2007. PMID 17655657
5. Cilio S, et al. Post-finasteride syndrome — a true clinical entity? Int J Impot Res. 2025. PMID 39953145
6. D'Amico AV, Roehrborn CG. Effect of 1 mg/day finasteride on concentrations of serum prostate-specific antigen in men with androgenic alopecia: a randomised controlled trial. Lancet Oncol. 2007. PMID 17196507
7. Piraccini BM, et al. Efficacy and safety of topical finasteride spray solution for male androgenetic alopecia: a phase III, randomized, controlled clinical trial. J Eur Acad Dermatol Venereol. 2022. PMID 34634163
8. Zhou Z, et al. The efficacy and safety of dutasteride compared with finasteride in treating men with androgenetic alopecia: a systematic review and meta-analysis. Clin Interv Aging. 2019. PMID 30863034
9. Gubelin Harcha W, et al. A randomized, active- and placebo-controlled study of the efficacy and safety of different doses of dutasteride versus placebo and finasteride in the treatment of male subjects with androgenetic alopecia. J Am Acad Dermatol. 2014. PMID 24411083
10. Olsen EA, et al. The importance of dual 5alpha-reductase inhibition in the treatment of male pattern hair loss: results of a randomized placebo-controlled study of dutasteride versus finasteride. J Am Acad Dermatol. 2006. PMID 17110217