Are there really risks with topical finasteride?

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. In the 2018 systematic review, there were reports of scalp irritation and dermatitis in a minority of topical finasteride users. Such reactions are typically managed by reducing application frequency, switching the formulation base (some compounded versions use different vehicles), or treating the dermatitis (e.g. with a steroid shampoo) if needed. 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. The systematic review by Lee et al. mentioned isolated cases of elevated liver enzymes in patients using topical finasteride. This could hint at a systemic effect or an idiosyncratic reaction (though finasteride is not generally known to be hepatotoxic). 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).

Thus, precautions are needed to avoid exposing pregnant partners – this is analogous to warnings for women handling crushed finasteride tablets.  Overall, topical finasteride’s side effect profile appears more favorable than oral finasteride’s. Most users do not experience systemic side effects, and those who do often report them as milder. A published literature review stated: “Topical finasteride reduces the potential for systemic side effects, including the risk of sexual dysfunction. The side effects are localized to the application site”. In practical terms, this means patients who could not tolerate oral finasteride due to sexual side effects might do well on topical finasteride without recurrence of those issues. However, it is crucial to counsel patients that topical finasteride is not entirely without risk a small percentage still get systemic side effects, and any concerning symptoms (sexual, psychological, etc.) should be monitored similarly to oral therapy.

One such report gathered 54 men with persistent sexual side effects; remarkably, 94% had low libido and 92% had erectile dysfunction continuing at least 3 months post-drug, along with depressive symptoms in many. While this was not a controlled study and has been met with some skepticism, it brought attention to possible lasting effects in a susceptible minority. Individual case reports within this spectrum include severe depression and even suicidal ideation purportedly triggered by finasteride use. The post-finasteride syndrome has led to the formation of patient advocacy groups and is an area of ongoing research. However, causality is hard to establish, and such outcomes are very rare relative to the large number of finasteride users.

Allergic Reactions:

Finasteride causing systemic allergic reactions is exceedingly uncommon. The case of a maculopapular rash mentioned earlier is one example. The 76-year-old 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. However, there are anecdotal case-like reports (on forums) of men experiencing significant side effects on topical finasteride – these will be discussed in the next section. In all, case reports illustrate that while finasteride is usually safe, rare adverse outcomes can occur. They remind clinicians and users to monitor for any unexpected symptoms (be it breast changes, mood changes, or allergic reactions). The level of evidence is low, so these reports don’t quantify risk but rather enumerate possibilities.

(Quality note: Case reports are uncontrolled observations and cannot prove causation. They often involve unusual circumstances or extreme reactions, so they should not be taken as representative of the average user experience. We include them here for comprehensive coverage, but the incidence of these issues is very low.)

In order to have a clearer comparison of what type of method to use, we must also talk about oral consumption.

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) is relatively low – on the order of 2% or less, which is only slightly higher than in men taking placebo For example, a long-term study reported sexual side effects in <2% of finasteride-treated men, a rate similar to placebo. However, post-marketing experience and independent studies suggest somewhat higher rates in real-world use. One one-year study found that 15% of men on finasteride reported sexual adverse effects vs 7% on placebo. This indicates there is a subset of men more susceptible to these effects. 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.

have also been associated with oral finasteride. Some users report mood swings, depression, or anxiety. In 2017, the UK’s MHRA issued a warning that finasteride has been associated with depressed mood, depression, and suicidal thoughts, though a direct causal link is unclear. At least  one controlled study found no statistical increase in depression with finasteride, but anecdotal reports and some surveys suggest it could affect mood in susceptible individuals. Thus, patients are advised to be vigilant for psychiatric symptoms. Other possible side effects include minor ones like headache, or in very rare instances, elevated liver enzymes or allergic reactions (e.g. rash). A published case report described a maculopapular drug eruption (widespread rash) that appeared two months after starting finasteride an unusual immune-mediated reaction. Such idiosyncratic reactions are extremely uncommon.

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

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