Finasteride

Understanding what DHT does

The story of finasteride begins before the tablet, with a question of physiology: why doesn't testosterone act in the same way in all tissues? Part of its effects are through its transformation into dihydrotestosterone. The enzyme which ensures this conversion, 5-alpha-reductase, then becomes an avenue for understanding the development of certain sexual characteristics and the functioning of tissues sensitive to androgens.

In 1974, Julianne Imperato-McGinley and her colleagues described an inherited deficiency of this enzyme in people studied in the Dominican Republic. These observations help distinguish the roles of testosterone and DHT. They do not yet demonstrate that a drug will preserve hair, but they provide a clue: modify a specific stage of hormonal metabolism rather than globally suppressing the action of androgens.

The prostate before the hair

Pharmaceutical development is exploring this avenue with 5-alpha-reductase inhibitors. The prostate, whose growth depends in particular on androgens, constitutes a first target. A trial published in 1992 in the New England Journal of Medicine shows that treatment with finasteride 5 mg can reduce the volume of the prostate and improve certain urinary disorders linked to its benign enlargement.

This usage explains why the same name exists with several dosages and indications. The prostate tablet is not just a more concentrated hair treatment. For alopecia, it is still necessary to establish the useful dose, observe the follicles and verify that the hormonal changes result in a visible difference. An action on an enzyme is not enough, in itself, to prove an aesthetic benefit.

Evaluate baldness treatment

Hair trials from the 1990s compared finasteride to a placebo in men with androgenetic alopecia. Two studies published in 1998 initially brought together 1,553 participants and notably evaluated hair counts and photographs. They show an advantage of treatment at 1 mg. In the United States, Propecia received approval for male pattern baldness on December 19, 1997.

Dose studies identify 1 mg per day as a suitable dosage for this indication, with no demonstrated capillary benefit in increasing to 5 mg. The five-year extensions then provide essential information: the difference with the placebo is maintained, while the loss progresses in the untreated group. Success is therefore not only measured by regrowth, but also by the hair that remains present over the years.

A setback that also concerns security

With wider use, monitoring is no longer limited to initial testing. Reports of persistent sexual effects and psychological disorders lead to reinforcement of the information. In 2025, the European re-evaluation confirms suicidal ideation as an adverse effect of tablets, of unknown frequency, while maintaining a favorable benefit-risk ratio in the authorized indications. This calls for an informed individual decision, not a trivialization of symptoms.

In France, the annual certificate implemented in 2026 formalizes this discussion before issuance. At the same time, dermal formulations seek to reduce general exposure by applying the drug to the scalp. The story therefore continues on two fronts: preserving effectiveness on the follicles and better controlling the risks. A new form may change this trade-off, but must be evaluated on its own.