Are there really risks with topical finasteride?

Topical finasteride is applied to the scalp instead of swallowed, with the aim of reaching the follicles while keeping blood levels low. It is a prescription medicine, and it is still finasteride. This article sets out what the published reports describe: the reactions specific to putting the drug on the skin, the rare systemic effects, the case-report evidence, and — for comparison — the better-documented side effects of the oral form.

Local skin reactions

The side effects unique to topical application are localized skin reactions. Because the solutions contain vehicles like alcohol, propylene glycol, or other solvents (similar to topical minoxidil solutions), they can irritate the skin. Documented local side effects include scalp itching (pruritus), redness, burning sensation, or contact dermatitis at the application site. These effects are usually mild to moderate and limited to the scalp. For instance, a patient might experience some dandruff or dry scalp from the topical formulation. Reviews of topical finasteride describe scalp irritation and dermatitis in a minority of users. Clinicians commonly respond by reducing the application frequency or changing the formulation base, since compounded versions use different vehicles; treating the dermatitis itself is a prescribing decision, so raise it with your prescriber rather than reaching for a medicated shampoo on your own. Allergic contact dermatitis to finasteride itself is very rare; most often it’s sensitivity to the vehicle.

Rare or Theoretical Risks:

Given the lower plasma levels with topical finasteride, one might expect virtually no systemic issues, but rare cases have been noted. Reviews of the topical literature have mentioned isolated cases of elevated liver enzymes in patients using topical finasteride. Whether this reflects a systemic effect or an idiosyncratic reaction is not established; finasteride is not generally regarded as hepatotoxic. We were not able to identify the primary case reports behind this claim, so treat it as an unconfirmed signal rather than a documented risk. Another consideration is that if a woman who is pregnant comes into contact with topical finasteride (e.g. via physical contact with treated scalp or hands), there is a risk to a male fetus (finasteride can cause abnormalities in male genital development).

Precautions are therefore needed to avoid exposing a pregnant partner, and they are the same in principle as the warnings about women handling crushed finasteride tablets.

The trial data on topical finasteride report much lower blood levels and a smaller reduction in serum DHT than the oral drug, and clinicians commonly describe the systemic side-effect profile as more favourable on that basis. That is a reasonable inference, but it is an inference: no study has been powered to measure whether sexual side effects are genuinely rarer on the topical form. Some men who stopped oral finasteride because of sexual side effects report tolerating the topical version, and some report the same problems on it. Topical finasteride is not risk-free. If you develop sexual, mood or other unexpected symptoms on it, treat that the same way you would on the oral drug: report it to your prescriber.

The most-cited such report is Irwig and Kolukula's 2011 interview study of 71 otherwise healthy men, aged 21 to 46, who reported new sexual side effects while taking finasteride for hair loss and whose symptoms persisted at least three months after they stopped. Among those men, 94% reported low libido and 92% reported erectile dysfunction, with decreased arousal in 92% and problems with orgasm in 69%. Note what that design does and does not show: the men were recruited because they had persisting symptoms, so the percentages describe that group, not the risk to an average user. The study was uncontrolled and has been met with scepticism, but it drew attention to possible lasting effects in a susceptible minority. Case reports in the same area describe severe depression and suicidal ideation attributed by the reporters to finasteride use. The MHRA's 2024 drug safety update reminds prescribers and patients of the risk of psychiatric side effects and of sexual side effects that may persist after treatment is stopped. Causality in individual cases is hard to establish, and the frequency of persistent effects is not known.

Allergic reactions

Systemic allergic reactions to finasteride are uncommon. Jia and Ran reported a maculopapular drug eruption in a 76-year-old patient. The patient developed a diffuse rash after 2 months on finasteride, which resolved after discontinuation and a course of steroids. A drug lymphocyte stimulation test was positive, supporting finasteride as the cause. Another patient in the same report had a similar rash onset 2 weeks after starting finasteride. These cases indicate that although finasteride is not a typical allergen, idiosyncratic hypersensitivity reactions can occur.

Topical finasteride: case observations

Published case reports specific to topical finasteride are sparse. There is mention (in a review) of a few cases where topical finasteride use corresponded with elevated liver enzymes. No formal case reports of sexual side effects purely from topical finasteride appear in the literature, likely because those instances would be managed by stopping the medication and might not be published. Community members do post accounts of significant side effects on topical finasteride, and those accounts are not published data. What the case-report literature shows is that rare adverse outcomes can occur, and that anyone using it should watch for unexpected symptoms — breast changes, mood changes, or allergic reactions — and report them. The level of evidence is low: these reports enumerate possibilities, they do not quantify risk.

(Quality note: Case reports are uncontrolled observations and cannot prove causation. They often involve unusual circumstances or extreme reactions, so they should not be read as representative of the average user's experience. They are included here because they are the only published evidence specific to the topical form.)

The oral form is far better documented, and it is the natural comparison.

Oral finasteride side effects

Finasteride’s best-known side effects are sexual dysfunction symptoms, due to its systemic DHT reduction. In controlled clinical trials for AGA, the incidence of drug-related sexual side effects (such as decreased libido, erectile dysfunction, reduced ejaculate volume) was reported as low, on the order of a few per cent, and close to the placebo rate. Post-marketing experience and some independent studies report higher rates in real-world use, and the reported figures vary widely between studies depending on how side effects were asked about. We have not been able to attach the specific trial percentages that previously appeared here to a source we could verify, so they have been removed rather than left standing. The sexual side effects usually reverse upon discontinuation of the drug, but there have been reports of persistent problems in some individuals (a contentious phenomenon termed “post-finasteride syndrome” or PFS). Case series of PFS have documented men with prolonged sexual dysfunction, where symptoms like low libido and ED lasted for months or years after stopping finasteride. While the existence and frequency of PFS are debated, regulatory agencies have added warnings about potential persistent sexual side effects.

Psychological side effects

Psychological effects have also been associated with oral finasteride. Some users report mood swings, depression, or anxiety. In April 2024 the UK's MHRA issued a drug safety update reminding prescribers and patients that finasteride has been associated with depressed mood, depression, and suicidal thoughts, and asked men taking it to stay vigilant for psychiatric and sexual side effects; the update does not establish a causal link. Controlled studies have not consistently shown an increase in depression with finasteride, while surveys and individual reports suggest it may affect mood in susceptible people. If your mood changes on finasteride, tell your doctor. Other possible side effects include minor ones like headache, or in very rare instances, elevated liver enzymes or allergic reactions (e.g. rash). Jia and Ran's case report described a maculopapular drug eruption (a widespread rash) that appeared two months after starting finasteride, an unusual immune-mediated reaction. Such idiosyncratic reactions are uncommon.

Before you use it

Topical and oral finasteride are both prescription-only medicines, and topical finasteride is in many places a compounded product whose strength and vehicle vary by pharmacy. Talk to a doctor or pharmacist before starting, stopping or combining finasteride in either form, and do not change the strength or frequency yourself. If you develop sexual, mood or cognitive symptoms, or a rash, contact your prescriber rather than waiting to see whether it passes.

Finasteride is contraindicated in pregnancy: it can cause abnormal development of the external genitals in a male fetus. A woman who is or may become pregnant must not take finasteride and must not come into contact with the topical solution or with crushed or broken tablets. Let the scalp dry fully and wash your hands after applying the topical form.

Sources

Jia, H., & Ran, L. (2023). Maculopapular drug eruption caused by finasteride: A case report. Clinical, Cosmetic and Investigational Dermatology, 16, 3359–3361. https://doi.org/10.2147/CCID.S426747

Irwig, M. S., & Kolukula, S. (2011). Persistent sexual side effects of finasteride for male pattern hair loss. The Journal of Sexual Medicine, 8(6), 1747–1753. https://doi.org/10.1111/j.1743-6109.2011.02255.x (PubMed 21418145)

Medicines and Healthcare products Regulatory Agency. (2024, April 29). Finasteride: Reminder of the risk psychiatric side effects and of sexual side effects (which may persist after discontinuation of treatment). GOV.UK. https://www.gov.uk/drug-safety-update/finasteride-reminder-of-the-risk-psychiatric-side-effects-and-of-sexual-side-effects-which-may-persist-after-discontinuation-of-treatment

Medicines and Healthcare products Regulatory Agency. (2024, April 29). Men on finasteride asked to stay vigilant for possible psychiatric and sexual side effects. GOV.UK. https://www.gov.uk/government/news/men-on-finasteride-asked-to-stay-vigilant-for-possible-psychiatric-and-sexual-side-effects

Mysore, V. (2012). Finasteride and sexual side effects. Indian Dermatology Online Journal, 3(1), 62–65. https://doi.org/10.4103/2229-5178.93496

Estill, M. C., Ford, A., Omeira, R., & Rodman, M. (2023). Finasteride and dutasteride for the treatment of male androgenetic alopecia: A review of efficacy and reproductive adverse effects. Georgetown Medical Review, 7(1). https://doi.org/10.52504/001c.88531