Finasteride & dutasteride · information only
The finasteride record, with the dates left in
Finasteride is argued about more than almost any medicine of its size. This site does something dull instead: it reads what the regulators actually published, keeps the date on every line, and says plainly where the evidence is still contested.
Eight regulator documents · all read at source on 24 September 2026
One enzyme, held shut
Testosterone
Circulating, doing its ordinary work
5α-reductase, type II
The label attributes two-thirds of circulating DHT to this type
DHT
Lower in blood and scalp while the drug is taken
A susceptible follicle
Balding scalp: smaller follicles, more DHT
Every figure and every warning on this site hangs off that one amber stop. Drawn from the FDA-approved labelling for finasteride, sections 12.1 and 12.2, revised November 2023.
What this site is
Reductase Review reads primary documents about one family of medicines: finasteride, dutasteride, and the topical versions that have grown up around them. Drug labels, safety bulletins, regulatory assessment reports. Each page states what a named body published, on what date, in its own words where the wording matters — and then says what that does and does not settle.
That sounds like a low bar. In this subject it is not. The two loudest positions online are that the drug is harmless and the complaints are psychosomatic, and that it is a catastrophe being covered up. Both are stated with total confidence and neither cites anything with a date on it. The documents are more careful than either camp, and considerably more interesting.
The eight documents this site is built on
Everything here rests on a short shelf of primary sources, read at their own publishers rather than summarised from a summary. The oldest is the US approval of the prostate tablet on 19 June 1992; the hair-loss tablet followed on 19 December 1997. Then a long quiet stretch, and then a cluster: a UK safety update and a patient card on 29 April 2024, an FDA compounding alert on 22 April 2025, an EU-wide decision on 22 August 2025, and the UK tightening its warnings again on 11 May 2026.
The paper trail, in the order it was written
Eight documents, each read at source- 19 June 1992FDAOral finasteride approved in the US for an enlarged prostate.
- 19 December 1997FDAA lower-strength tablet approved for male pattern hair loss in men.
- March 2016Medsafe (NZ)A prescriber bulletin uses the name post-finasteride syndrome.
- November 2023FDA labelCurrent US labelling: persistent sexual dysfunction, depression and suicidal ideation listed from post-approval reports.
- 29 April 2024MHRA (UK)Safety update and a patient card in every pack.
- 22 April 2025FDACompounding risk alert: no approved topical finasteride exists in the US.
- 22 August 2025European CommissionEU-wide decision after the PRAC review; suicidal ideation confirmed as a side effect of the tablets.
- 11 May 2026MHRA (UK)Warnings strengthened again; a precautionary note added to dutasteride.
Read in order, the record is not a scandal and it is not a clean bill of health. It is a regulator system slowly deciding that the warnings it already had were not reaching the people taking the medicine.
Three rules this site keeps
They are unusual enough to be worth stating on the front page, because they explain what you will not find here.
- No doses, anywhere. Not in prose, not in a table, not quoted off a label as though the label were talking to you. What strength, for whom, and whether at all, is a prescriber's decision made with your history in front of them.
- No medical reviewer, and no pretending. Nobody clinical has read this site. The niche is full of pages stamped with a doctor's name and a photograph; inventing one would be the easiest lie available here, so there is a note near the top of every page saying exactly what this is.
- No link that sells you a medicine. Two commission links exist on this site, both to services that run a consultation, both on one page, both disclosed where they sit. The routes worth trying first cost this site its entire income and are named first anyway.
Where to start
If you are deciding whether to have the conversation with a doctor at all, start with what finasteride is and what its licence covers. If you are already taking it and something has changed, go to the side-effect record, which is organised by what kind of evidence each effect rests on. If you arrived because of something you read about post-finasteride syndrome, that has its own page, and it is the most carefully written thing here.
Every page on file
The full index →How finasteride works on DHT, and what else that enzyme does
The mechanism is simple enough to draw. The interesting part is what else 5-alpha-reductase is doing, because that is where every argument about side effects starts.
Sep 24, 2026Finasteride vs minoxidil: not the same kind of decision
One is a prescription tablet acting on a hormone pathway; the other is an over-the-counter topical that does not. Comparing them on effectiveness alone misses the point.
Sep 23, 2026Finasteride, pregnancy exposure and male fertility
The least ambiguous section of the whole label, and the one most often skipped: who must not handle the tablets, what the semen study found, and what recovers.
Sep 22, 2026What happens when you stop taking finasteride
The label answers the hair question in one sentence and the trials show the shape of it. The other question — symptoms that do not stop — is answered far less cleanly.
Sep 21, 2026Does finasteride regrow hair, or does it hold the line?
The trial data answers this precisely, and the answer is mostly the second one. Here are the counts, the photograph ratings and the reason the placebo column matters most.
Sep 20, 2026Finasteride and minoxidil together: two drugs, two regulators, one scalp
They work by unrelated mechanisms and sit in different regulatory categories. What combining them changes most is your ability to tell which one caused anything.
Sep 19, 2026