What is Finasteride?
Finasteride is a synthetic active ingredient originally developed to treat benign prostatic hyperplasia. [1] The breakthrough came in 1992 when the US Food and Drug Administration (FDA) approved finasteride for treating benign prostatic hyperplasia. Five years later, in 1997, approval followed for treating male pattern hair loss. [2]
Today, finasteride is available in various dosages (oral and topical). This article focuses on the mechanism of action and scientific evidence of efficacy, independent of the dosage form. For a detailed comparison of different application forms, read our article Finasteride Topical vs. Oral.
Mechanism of Action of Finasteride Against Hair Loss
To understand how finasteride works, we must first examine the biological mechanisms of hair loss.
DHT as the Main Enemy of Hair Follicles
The main culprit in androgenetic hair loss is a hormone called dihydrotestosterone (DHT). DHT is formed when the enzyme 5α-reductase type II converts the male hormone testosterone. [3] The problem: DHT is about ten times more potent than normal testosterone and binds particularly strongly to hair follicle receptors. [4]
In people with genetic predisposition, DHT leads to progressive miniaturization of hair follicles:
- The growth phase (anagen phase) is shortened
- Hair follicles become smaller and thinner
- Strong terminal hairs become fine vellus hairs
- Eventually follicles stop growing entirely
Finasteride Blocks DHT Production
This is where finasteride comes in: It inhibits the enzyme 5α-reductase type II and thus prevents the conversion of testosterone to DHT. The effects are measurable: [5] DHT reduction in the scalp is 64-69%, explaining the local effect on hair follicles. In the blood, DHT is reduced by about 70%, showing the systemic effect. Importantly, testosterone levels remain normal and unchanged. Finasteride only lowers DHT, not testosterone. Normal testosterone levels are preserved, so typical male characteristics are not affected.
Additional Effects at the Cellular Level
Recent research shows that finasteride not only works through DHT reduction but also acts directly on hair follicles. Finasteride protects hair follicle cells from apoptosis, or programmed cell death, and activates survival signals in cells surrounding the hair roots. [6] The active ingredient also extends the anagen phase and shortens the catagen phase, so hairs remain in the productive growth phase longer. [7] Additionally, finasteride stimulates cellular signaling pathways essential for hair growth and promotes stem cell signals in dermal papilla cells. [8] These combined mechanisms explain why finasteride not only stops hair loss but also leads to regrowth in many users.
Clinical Studies and Scientific Evidence
The efficacy of finasteride has been investigated in numerous clinical studies over more than two decades.
The Landmark Study of 1998
The most important finasteride study was published in 1998 in the Journal of the American Academy of Dermatology. [9] This multicenter, placebo-controlled study examined over 1,500 men with androgenetic alopecia over two years. The study design included 1,553 men between 18 and 41 years, randomized into a finasteride group (1 mg daily) or placebo group. The study was double-blind with primary endpoints of hair count and hair growth.
The results after 12 months were clear and showed a distinct difference between the finasteride and placebo groups:
| Parameter | Finasteride | Placebo |
|---|---|---|
| Improvement (physician assessment) | 48% | 7% |
| No change | 42% | 25% |
| Worsening | 10% | 68% |
After 24 months, positive effects continued: 66% of the finasteride group showed improvement compared to only 7% in the placebo group. Hair count increased continuously and improvements stabilized at a high level.
5-Year Long-Term Study
A follow-up study tracked participants over five years. [10] The results were impressive: 65% of users showed visible hair regrowth, 35% stabilized hair loss without further deterioration, and only 5% showed progressive hair loss despite treatment. Maximum effect was achieved after 12-24 months and remained stable thereafter.
Lower Dosages
Studies showed that lower dosages than the standard 1-mg dose can also be effective. [11] Detailed information on various dosages (oral and topical) can be found in our article Finasteride Prescription Switzerland.
When Are First Results Visible?
Finasteride's effect sets in with delay and develops gradually. In the first 0-3 months, you're in the stabilization phase where active hair loss stops and many users already notice fewer hairs falling out. After 3-6 months, first visible improvements become apparent when first fine hairs (vellus hairs) become visible and hair density begins to improve. Between months 6 and 12, significant improvement shows as vellus hairs become terminal hairs and hair density visibly increases. After 12-24 months, maximum effect is finally achieved and hair density stabilizes at the new level.
Finasteride therapy requires patience. Users should wait at least 12 months before judging efficacy. Premature discontinuation can result in missing potential successes.
Who Benefits Most from Finasteride?
Finasteride's efficacy varies depending on individual profile and hair loss stage.
Ideal Candidates
Finasteride works best in men between 18 and 60 years in early stages of hair loss (Norwood-Hamilton II-V). Treatment shows particularly good results with hair loss at the crown and vertex as well as with actively progressing hair loss where follicles are still active. In already bald areas, effect is significantly limited as follicles there are often completely inactive.
Less Suitable
Finasteride works less well with completely bald areas, as follicles there are already inactive. Also with very advanced hair loss (Norwood-Hamilton VI-VII) or with non-androgenetic alopecia like alopecia areata, no effect is shown.
Finasteride cannot reactivate already inactive hair follicles. The earlier treatment begins, the better the results. Best results show in users who still have active, though miniaturized, hair follicles.
Use in Women
Data on finasteride in women is limited. Smaller studies show evidence of efficacy in postmenopausal women at higher doses of 5 mg. [12] In premenopausal women, there is insufficient evidence, plus contraindication due to pregnancy risk. In pregnancy, finasteride is absolutely contraindicated due to significant risk of malformations. In Switzerland, finasteride is not approved for women and is only used off-label in postmenopausal women.
What Happens After Discontinuation?
An important point users must understand: Finasteride's effect only persists with continuous use. After discontinuing the medication, hair loss returns within 3-6 months, the hair picture develops to the level that would have been reached without treatment, and already gained hairs are lost again. Finasteride is thus a long-term therapy where the medication must be applied permanently to maintain results. This doesn't mean the medication is addictive, but that the underlying biological process of hair loss resumes without DHT blockade.
Conclusion on Finasteride Efficacy
The scientific evidence for finasteride is clear: It is one of the most effective active ingredients against androgenetic hair loss. Study data shows high success rates where 2 out of 3 users experience regrowth, while almost all users stop active hair loss and achieve good stabilization. Effects remain stable over years showing proven long-term efficacy. Best results are achieved with early treatment start when follicles are still active.
For practical information on access and application see Finasteride Prescription Switzerland. Information on side effects can be found under Finasteride Side Effects. For a comparison of dosage forms, read our article Finasteride Topical vs. Oral. You can also start an online consultation or learn more about the causes of hair loss.