Finasteride

What finasteride is

Finasteride is a prescription-only inhibitor of 5-alpha reductase type II. In Germany it is approved in two strengths: 1 mg for hereditary hair loss (androgenetic alopecia), 5 mg for benign prostatic enlargement. For early hereditary hair loss there is also a spray for application to the scalp.

What is rated is the state of knowledge. Finasteride has been in use for decades, the effect on hair has been counted in blinded trials, and the side effects are well documented from approval trials and long-term use. In 2025 a European review procedure expanded the product information.

How it works

Finasteride inhibits 5-alpha reductase type II and thereby reduces the conversion of testosterone to dihydrotestosterone (DHT), both in the blood and in the scalp. DHT is the hormone that makes hair follicles shrink in hereditary hair loss.

The chain of action is well described in humans. It also explains why the effect lies mainly in slowing things down: in the placebo group hair loss continued, under finasteride it was slowed, and additional hairs grew back.

What the studies show

Kaufman 1998: two blinded trials

Kaufman 1998 (J Am Acad Dermatol) summarizes two one-year, placebo-controlled trials with 1,553 men aged 18 to 41, 1,215 of whom remained in the blinded extension. Hairs were counted on 5.1 square centimeters at the vertex, with a baseline of 876 hairs. Under finasteride, hair count was 107 above placebo after one year and 138 after two years, p<0.001. The authors described the side effects in these trials as minor.

What the 107 hairs mean

Measured against the baseline of 876 hairs, the difference after one year corresponds to roughly twelve percent. This value was calculated from the trial figures and is not stated in the abstract. The difference also arises because the placebo group continued to lose hair.

The European review procedure of 2025

In 2025 the safety committee of the European Medicines Agency reviewed studies, case reports and the European adverse reaction database EudraVigilance. It found 325 relevant cases of suicidal thoughts, 313 of them for finasteride and 13 for dutasteride, with one case involving both. Most cases concerned patients treated for hair loss. Suicidal thoughts were confirmed as a side effect of the 1 mg and 5 mg tablets; their frequency is considered impossible to estimate. According to this assessment, the benefits continue to outweigh the risks for all approved uses.

Where the data stop

• How common suicidal thoughts are. The frequency is explicitly unknown; it cannot be estimated from the available data. Case reports show that the side effect exists, not how often it occurs.
• The “post-finasteride syndrome”. It is not established as a clinical entity. The largest analysis on it was conducted in men over fifty on the higher dose and cannot be transferred to young users.
• Who was studied. The approval trials included men aged 18 to 41 and counted hairs at the vertex. For other groups and regions of the scalp, these trials say nothing directly.
• The spray. For the finasteride spray on the scalp, the review procedure found no evidence of a link with suicidal thoughts, and its product information was not changed. That is an absence of evidence, not proof of safety.

Status, approval and legal

Finasteride is approved in Germany: 1 mg for androgenetic alopecia, 5 mg for benign prostatic enlargement. It is prescription-only and belongs in the hands of a physician, also because of the psychiatric side effects.

On September 15, 2025, a Dear Doctor letter (Rote-Hand-Brief) was issued by the Federal Institute for Drugs and Medical Devices (BfArM) in coordination with the European Medicines Agency. Since then, suicidal thoughts have been listed as a side effect of orally administered finasteride in the product information. Packs of 1 mg now include a patient card that serves as a reminder of these risks and says what to do.

Safety

Since 2025, suicidal thoughts have been confirmed as a side effect of the tablets; their frequency is unknown. They were reported mostly by men taking finasteride for hair loss. According to the Dear Doctor letter, patients taking it for hair loss should stop treatment and seek medical advice if they experience depressed mood, depression or suicidal thoughts.

Sexual dysfunction such as reduced libido or erectile dysfunction is the best-known side effect and the most common reason for stopping. It can contribute to mood changes. Here, too, the product information for 1 mg now explicitly calls for medical advice.

The safety score of 8 in the BK-Score rates the data, not the danger. Anyone who has suicidal thoughts can reach the German crisis line Telefonseelsorge free of charge around the clock at 0800 111 0 111.

Sources

• Kaufman KD et al., J Am Acad Dermatol 1998 – finasteride in androgenetic alopecia, two trials with 1,553 men
• EMA, review of finasteride- and dutasteride-containing medicines 2025 – suicidal thoughts confirmed as a side effect of finasteride
• BfArM, Dear Doctor letter (Rote-Hand-Brief) on finasteride and dutasteride of September 15, 2025 – suicidal thoughts