Finasteride: Efficacy & Clinical Studies for Hair Loss

What is Finasteride?

Finasteride is an active ingredient originally developed for treating benign prostatic enlargement and was approved by the US Food and Drug Administration (FDA) for this application in 1992. ^[1] Five years later, in 1997, approval for male pattern hair loss followed. ^[2] Today, finasteride is available in various dosages (oral and topical). This article focuses on the mechanism of action and scientific evidence for efficacy, independent of the form of administration. For a detailed comparison of different application forms, read our article on topical vs. oral finasteride.

Mechanism of Action of Finasteride Against Hair Loss

To understand how finasteride works, we must first look at the biological mechanisms of hair loss.

DHT: The Hormone That Causes Hair Loss

The main trigger in hereditary hair loss is the hormone dihydrotestosterone (DHT). Learn more about hair loss causes in our fundamentals article. DHT is the central factor in androgenetic alopecia. DHT is formed when the enzyme 5α-reductase type II converts the hormone testosterone. ^[3] The problem: DHT is about ten times more potent than normal testosterone and binds particularly strongly to the hair follicles. ^[4]

In people with the corresponding predisposition, DHT causes the hair follicles to gradually become smaller. First, the growth phase is shortened. The hair follicles then become smaller and thinner. Strong hairs become fine vellus hairs. Eventually, the follicles stop growing completely.

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: In the scalp, DHT decreases by 64 to 69%, which explains the effect on hair follicles. In the blood, DHT is reduced by about 70%. ^[5]

Important: Testosterone levels remain normal and unchanged. Finasteride only lowers DHT, not testosterone. Therefore, typical male characteristics remain unaffected.

Additional Positive Effects on Hair Follicles

Recent research shows that finasteride not only lowers DHT but also acts directly on hair follicles. The active ingredient protects the cells of hair follicles from dying and extends the growth phase of the hairs. ^[6] ^[7] At the same time, it activates important signaling pathways for hair growth and promotes stem cells in the hair roots. ^[8]

These combined effects explain why finasteride not only stops hair loss but also leads to new hair growth 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 Most Important Study from 1998

The most important study on finasteride was published in 1998 in the Journal of the American Academy of Dermatology. ^[9] This study examined over 1,500 men with hereditary hair loss over two years. A total of 1,553 men between 18 and 41 years participated, who were randomly divided into a finasteride group (1 mg daily) or placebo group. The study was conducted double-blind, meaning neither participants nor doctors knew who received the real medication. The main goal was to measure hair count and hair growth.

The results after 12 months were clear and showed a distinct difference between the finasteride and placebo groups:

Efficacy of finasteride after 12 months of treatment (n=1,553) ^[9]
Parameter	Finasteride	Placebo
Improvement (physician assessment)	48%	7%
No change	42%	25%
Deterioration	10%	68%

After 24 months, the positive effects continued: 66% of the finasteride group showed improvement, compared with only 7% in the placebo group. Hair count continued to increase and improvements remained stable.

Long-term Study Over 5 Years

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. Only 5% showed progressive hair loss despite treatment. Maximum efficacy occurred after 12 to 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 on finasteride prescriptions.

When Are First Results Visible?

The effect of finasteride is delayed and develops gradually. In the first 0 to 3 months, you are in the stabilization phase, where active hair loss stops. Many users already notice that fewer hairs are falling out.

After 3 to 6 months, the first visible improvements become apparent. First fine hairs become visible and hair density begins to improve. Between months 6 and 12, significant improvement is seen, where fine hairs become thicker and hair density visibly increases.

After 12 to 24 months, maximum efficacy is reached. Hair density stabilizes at the new level.

Realistic Expectations

Therapy with finasteride requires patience. Users should wait at least 12 months before assessing efficacy. Premature discontinuation can result in missing potential successes.

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Who Benefits Most from Finasteride?

The efficacy of finasteride varies depending on individual profile and stage of hair loss.

Who Benefits Most?

Finasteride works best in men between 18 and 60 years in early stages of hair loss. Particularly good results are seen in hair loss at the crown and top of the head as well as in actively progressing hair loss where hair follicles are still active. In already bald areas, the effect is limited because hair follicles there are often already inactive.

When Does Finasteride Not Work?

Finasteride shows no or little effect in completely bald areas because hair follicles there are already inactive. Even with very advanced hair loss, success prospects are limited. For circular hair loss (alopecia areata) or other forms of non-hereditary hair loss, finasteride does not work.

Important to Know

Finasteride cannot reactivate already inactive hair follicles. The earlier treatment begins, the better the results. The best outcomes are seen in users who still have active, albeit miniaturized, hair follicles.

Use in Women

Data for 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 data. Additionally, there is a contraindication due to pregnancy risk.

During pregnancy, finasteride is absolutely contraindicated because there is a significant risk of malformations. In Switzerland, finasteride is not approved for women and is only used in exceptional cases in postmenopausal women.

What Happens After Discontinuation?

An important point: The effect of finasteride only persists with continuous use. After discontinuing the medication, hair loss returns within 3 to 6 months. The hair pattern develops to the level that would have been reached without treatment. Already gained hairs are lost again.

Finasteride is therefore a long-term therapy. The medication must be used permanently to maintain results. This does not mean the medication is addictive. It only means that the 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 hereditary hair loss. The study data shows that new hair growth occurs in 2 out of 3 users. Active hair loss stops in almost all users. The effects remain stable over years. The best results are achieved with early treatment when hair follicles are still active.

For practical information on obtaining and using finasteride, see our articles on finasteride prescriptions and finasteride side effects. For a comparison of forms of administration, read our article on topical vs. oral finasteride. You can also start an online consultation or learn more about the causes of hair loss.