Finasteride and dutasteride: where is the difference?
Both inhibit the same enzyme. Why stronger DHT suppression does not automatically mean better results.
Both drugs belong to the same class and both intervene at the same point in hormone metabolism, yet the idea persists that one is fundamentally superior to the other. The reasoning usually goes: dutasteride lowers DHT more, so it works better.
That calculation does not hold. The reason lies in the question of where in the body the DHT is being lowered.
Why DHT is central to hereditary hair loss
In androgenetic hair loss, genetically sensitive follicles react to dihydrotestosterone, or DHT. Under its influence the growth phase shortens and the follicle miniaturises progressively over successive cycles.
DHT is not produced directly but converted from testosterone. The enzyme that catalyses this conversion is 5-alpha-reductase. Drugs that inhibit it are called 5-alpha-reductase inhibitors, and finasteride and dutasteride are the two best known.
Three isoenzymes, three areas of responsibility
The decisive point usually missing from the discussion: 5-alpha-reductase is not a single enzyme but exists in three variants. All three convert testosterone into DHT, but they are active in different tissues.
| Isoenzyme | Where it is active | Relevance to the scalp |
|---|---|---|
| Type 1 | Sebaceous glands, liver | No established role at the scalp. |
| Type 2 | Scalp, prostate | The isoenzyme that matters for hair loss. |
| Type 3 | Maturation processes in the body | No known activity at scalp or prostate. |
Here is the crux: finasteride inhibits types 2 and 3. Dutasteride additionally inhibits type 1, which lowers circulating DHT by roughly 30 per cent more.
Why more suppression does not automatically mean more effect
The additional inhibition largely concerns type 1, the isoenzyme active in the sebaceous glands and liver, not at the scalp. For the target tissue in hair loss, that extra suppression brings no demonstrated advantage.
Another indication supports this logic. In treating benign prostatic hyperplasia, also a type 2 dependent condition, dutasteride has not been shown to be more effective than finasteride despite lowering DHT further.
What matters is not how much DHT is lowered overall, but whether it is lowered where the problem sits.
A side effect rarely discussed
When the conversion of testosterone to DHT is inhibited, testosterone accumulates and serum levels rise. Testosterone acts far more weakly on sensitive follicles than DHT, but it is not inert.
With stronger DHT suppression, correspondingly more free testosterone is available, some of which is converted to oestrogen via the enzyme aromatase. That is one possible explanation, not yet confirmed in controlled trials, for why some users report no improvement or even deterioration on the more potent drug.
This remains hypothetical. But it illustrates that in endocrinology, stronger is rarely the same as better.
Tolerability
Both are among the most widely prescribed drugs in their class worldwide. In the licensing trials the rate of reported adverse effects was in the low single-digit percentages, and symptoms generally resolved after stopping.
At the same time there is a contested discussion about persistent symptoms after discontinuation, which is not scientifically settled. Anyone considering treatment should weigh benefits and risks individually with a doctor, rather than being pushed either way by forum reports.
Women of childbearing age must not come into contact with either substance, as absorption through the skin is possible and can cause malformations in a male foetus.
Where drug therapy reaches its limit
Drugs of this class work for as long as they are used, and they work on follicles that are still present. Where no functioning roots remain, no substance can produce hair.
At that point the question shifts from preservation to restoration, and therefore to transplanting genetically resistant follicles from the back of the head. An overview is in our comparison of FUE and FUT.
Frequently asked questions
What is the main difference between finasteride and dutasteride?
Finasteride inhibits 5-alpha-reductase types 2 and 3; dutasteride additionally inhibits type 1. Since type 2 is the isoenzyme active at the scalp, the extra inhibition largely affects other tissues.
Is stronger DHT suppression better for hair?
Not necessarily. What counts is inhibition at the scalp, not the total figure in the blood.
Can 5-alpha-reductase inhibitors bring back lost hair?
They extend the growth phase and can slow miniaturisation. Follicles already completely lost cannot be restored this way.
Are these drugs available without prescription?
No. Both are prescription-only and may be used only on medical direction.
Individual advice rather than forum wisdom
Which strategy makes sense for you depends on the stage, the diagnosis and your personal circumstances.
Arrange a consultationThis article is for general information and does not replace medical advice or diagnosis. Decisions about medication and individual treatment are made only in a personal consultation with a doctor.
