Hair and scalp evidence

Finasteride: Mechanism, Approved Label, and Topical Literature

Reviewed by ExaVeyra Sciences editorial team · Updated 15 September 2026

Finasteride is a competitive inhibitor of type II 5-alpha-reductase, the enzyme that converts testosterone to dihydrotestosterone in the hair follicle and the prostate. An approved oral product carries an FDA label whose indication is male pattern hair loss in men, no topical finasteride product is FDA-approved, and in April 2025 the FDA alerted providers, compounders and consumers to adverse event reports associated with compounded topical products. This page sets out the mechanism, what the label states, what the topical literature reports, and what the agency has said, in that order.

It is an evidence reference rather than a product page. The compounded hair and scalp formulations page on this site lists the topical solutions the 503A pharmacy partner can prepare to prescription and how each is dated; the oral tablet is an approved product dispensed against an ordinary prescription, and this page says nothing about which a prescriber should choose.

Mechanism: one enzyme, two isoforms, one of them in the follicle

Testosterone is converted to dihydrotestosterone by 5-alpha-reductase, which exists as two principal isoforms. Type I predominates in sebaceous glands and skin; type II predominates in the prostate and in the dermal papilla of scalp hair follicles. Finasteride inhibits type II selectively, and the approved label describes a reduction in scalp and serum dihydrotestosterone as its pharmacodynamic effect.

The follicle connection runs through the dermal papilla, the cluster of mesenchymal cells at the base of each follicle that regulates the growth cycle. In androgenetic alopecia the papilla of a susceptible follicle responds to dihydrotestosterone by shortening the growth phase over successive cycles until the follicle miniaturises, which is why the pharmacology of the enzyme is discussed in the literature in the context of that condition rather than of hair biology in general.

What the approved oral label states

The approved one-milligram oral product is indicated, in the words of its label, for male pattern hair loss in men only. The label states that daily use for three months or more is generally necessary before benefit is observed, that continued use is recommended to sustain benefit, and that the product is not indicated for women or children. It carries contraindications in pregnancy, a warning about exposure of pregnant women to crushed or broken tablets, and a description of its effect on prostate-specific antigen measurements.

The label was revised in 2012 to describe sexual adverse reactions that persisted after discontinuation, and the current prescribing information lists depression and suicidal ideation among reported adverse events. Those sections are reproduced in full on DailyMed, which is linked below, and they are a prescriber matter. A supplier can state what the label says and where to read it; the counselling conversation belongs to the prescriber.

A five-milligram oral tablet also exists and is approved for benign prostatic hyperplasia; it is outside the scope of this page, which describes only the one-milligram label, because that is the one whose indication is hair.

What the systematic reviews report for the oral product

The 2017 systematic review and meta-analysis by Adil and Godwin in the Journal of the American Academy of Dermatology pooled randomised trials of the three most studied interventions for androgenetic alopecia and reported that oral finasteride, topical minoxidil and low-level laser light each outperformed placebo on hair count. It is the reference most often cited for the position that the approved actives have trial evidence behind them, and it is cited here for that reason.

Two pharmacovigilance analyses of the FDA Adverse Event Reporting System were published in 2025. Zhong and colleagues in PLoS One analysed reports from 2004 to April 2024 across organ systems, and Thaibah and colleagues in Pharmaceuticals examined suicidality signals specifically. Both are analyses of spontaneous reports rather than of trial data, and the study design badge beside each citation below says so. The European Medicines Agency added suicidal ideation to the product information for finasteride in May 2025.

What the topical literature reports, and what it does not create

The rationale for topical finasteride is that scalp dihydrotestosterone can be lowered with less systemic exposure than the oral tablet produces. A 2022 phase III randomised controlled trial by Piraccini and colleagues in the Journal of the European Academy of Dermatology and Venereology studied a 0.25% finasteride spray solution in men with androgenetic alopecia and reported target-area hair count gains over vehicle at 24 weeks, with serum dihydrotestosterone reductions smaller than those reported for the oral tablet.

A 2025 systematic review and meta-analysis in Frontiers in Medicine pooled seven randomised trials, 396 participants in total, comparing a mixed minoxidil and finasteride solution with minoxidil solution alone in men, and reported that the combination outperformed minoxidil alone on hair density, hair diameter and global photographic assessment. The compounded solutions on this site pair 0.1% finasteride with 5% minoxidil, a lower finasteride concentration than the phase III spray studied.

Neither finding creates an approved product. No topical finasteride formulation is FDA-approved, and a compounded topical solution is prepared under section 503A to an individual prescription without FDA review of its safety, effectiveness or quality. The literature describes what was studied; it does not change what the product is.

The FDA alert on compounded topical finasteride

The alert also recorded that many of the consumers in those reports stated they had not been told of the potential risks by the prescriber, and in some cases had been told the topical form carried none. That is the sentence in the alert with the most operational content for a practice, because it describes a counselling failure rather than a pharmacological one, and the alert is linked in full in the sources below.

Every page on this site that discusses topical finasteride cites the alert, and the compounded hair and scalp formulations page describes the topical solutions by their composition and dating only.

How the two forms sit in a formulary

The oral tablet and the topical solution are different products with different dating, and a practice that orders both holds them as separate line items. Which form, if either, suits a given patient is a prescribing decision that this page does not take part in.

Sources

1. DailyMed, finasteride tablet 1 mg, prescribing information (National Library of Medicine) (accessed 15 September 2026)
2. FDA, finasteride 1 mg tablets, 2012 revised label (Drugs@FDA, NDA 020788) (accessed 15 September 2026)
3. FDA alerts health care providers, compounders and consumers of potential risks associated with compounded topical finasteride products (April 22, 2025) (accessed 15 September 2026)
4. FDA, Compounding and the FDA: Questions and Answers (accessed 15 September 2026)

Scientific literature

Each source carries the kind of study it was and, where the study enrolled people, how many. Study design decides what a result can establish, so it is stated rather than left to be inferred. Each line also says what that source is carrying on this page.

1. Adil A, Godwin M The effectiveness of treatments for androgenetic alopecia: a systematic review and meta-analysis. Journal of the American Academy of Dermatology, 2017. doi:10.1016/j.jaad.2017.02.054 PMID:28396101Meta-analysisSource 1 supports: The pooled randomised evidence that oral finasteride and topical minoxidil each outperformed placebo on hair count, cited for the position that the approved actives have trial evidence behind them.
2. Piraccini BM, Blume-Peytavi U, Scarci F, et al. Efficacy and safety of topical finasteride spray solution for male androgenetic alopecia: a phase III, randomized, controlled clinical trial. Journal of the European Academy of Dermatology and Venereology, 2022. doi:10.1111/jdv.17738 PMID:34634163Randomised controlled trial458 participantsSource 2 supports: The phase III trial of a 0.25% topical finasteride spray, cited for the target-area hair count result and the smaller serum dihydrotestosterone change than the oral tablet.
3. Frontiers in Medicine (Lausanne), 2025 Comparing minoxidil-finasteride mixed solution with minoxidil solution alone for male androgenetic alopecia: a systematic review and meta-analysis of randomized controlled trials. Frontiers in Medicine, 2025. PMID:41127390Meta-analysis396 participantsSource 3 supports: The pooled comparison of a mixed minoxidil and finasteride solution against minoxidil alone across seven randomised trials, cited for the density, diameter and global assessment results.
4. Zhong X, et al. Multidimensional assessment of adverse events of finasteride: a real-world pharmacovigilance analysis based on FDA Adverse Event Reporting System (FAERS) from 2004 to April 2024. PLoS One, 2025. doi:10.1371/journal.pone.0309849 PMID:40127098Clinical studySource 4 supports: A spontaneous-report analysis across organ systems, cited so a reader can see that the adverse event signals discussed here rest on pharmacovigilance data rather than on trial data.
5. Thaibah HA, et al. Suicidality risks associated with finasteride, a 5-alpha reductase inhibitor: an evaluation of real-world data from the FDA Adverse Event Reports. Pharmaceuticals (Basel), 2025. doi:10.3390/ph18070957 PMID:40732247Clinical studySource 5 supports: The pharmacovigilance evaluation of suicidality signals, cited alongside the label revisions so the prescriber-facing safety literature is visible on the same page as the efficacy literature.
6. Kanti V, Messenger A, Dobos G, et al. Evidence-based (S3) guideline for the treatment of androgenetic alopecia in women and in men - short version. Journal of the European Academy of Dermatology and Venereology, 2018. doi:10.1111/jdv.14624 PMID:29178529Clinical guidelineSource 6 supports: The European S3 guideline, cited for where oral finasteride sits in a formal evidence-graded recommendation for men and for its position on women.
7. Gupta AK, Venkataraman M, Talukder M, Bamimore MA Relative efficacy of minoxidil and the 5-alpha reductase inhibitors in androgenetic alopecia treatment of male patients: a network meta-analysis. JAMA Dermatology, 2022. doi:10.1001/jamadermatol.2021.5743 PMID:35107565Meta-analysisSource 7 supports: The network meta-analysis ranking minoxidil and the 5-alpha-reductase inhibitors against one another in men, cited for the comparative picture the single-agent trials cannot give.
8. Suchonwanit P, Iamsumang W, Leerunyakul K Topical finasteride for the treatment of male androgenetic alopecia and female pattern hair loss: a review of the current literature. Journal of Dermatological Treatment, 2022. doi:10.1080/09546634.2020.1782324 PMID:32538225Narrative reviewSource 8 supports: The review of the topical finasteride literature before the phase III trial published, cited for the pharmacokinetic rationale of the topical route.
9. Devjani S, Ezemma O, Kelley KJ, et al. Androgenetic alopecia: therapy update. Drugs, 2023. doi:10.1007/s40265-023-01880-x PMID:37166619Narrative reviewSource 9 supports: A current therapy update, cited for how the approved oral product and the topical form are positioned relative to one another in the specialist literature.
10. Gupta AK, Bamimore MA, Williams G Finasteride use: evaluation of depression and suicide risk. Journal of Cosmetic Dermatology, 2025. doi:10.1111/jocd.70102 PMID:40082195Narrative reviewSource 10 supports: An evaluation of the depression and suicide signal, cited beside the pharmacovigilance analyses so the prescriber-facing safety literature is complete on this page.
11. Landells I, Chow E, Gupta AK, et al. A Canadian consensus on androgenetic alopecia: approach and management. Journal of Cutaneous Medicine and Surgery, 2025. doi:10.1177/12034754251368849 PMID:40986632Consensus statementSource 11 supports: A 2025 consensus statement, cited for the current specialist position on finasteride in an approach to pattern hair loss.