Finasteride and dutasteride both work by lowering DHT, the hormone that shrinks genetically sensitive hair follicles in pattern hair loss. Dutasteride is the stronger of the two, and it's increasingly prescribed off-label. Here's how they compare, in question-and-answer form.
How are they different?
Both block 5-alpha reductase, the enzyme that converts testosterone into DHT. Finasteride blocks only the type 2 form of the enzyme. Dutasteride blocks both type 1 and type 2. The practical result is that dutasteride lowers DHT much further: roughly 90% or more in the blood, compared with about 70% for finasteride.
Is dutasteride approved for hair loss?
Not in the United States. Oral finasteride 1 mg is FDA-approved for male pattern hair loss. Dutasteride 0.5 mg is FDA-approved only for an enlarged prostate. When American doctors prescribe it for hair loss, it's off-label. Dutasteride 0.5 mg is approved for male pattern hair loss in South Korea, Japan and Taiwan; South Korea approved it in 2009.
Does dutasteride work better?
The evidence leans that way. A large randomized trial found dutasteride 0.5 mg increased hair count more than finasteride 1 mg at 24 weeks, and later reviews and a long-term chart review of hundreds of Korean patients reached similar conclusions. It's often considered by men who haven't responded well enough to finasteride.
Are the side effects different?
The possible side effects are similar in kind: decreased libido, erectile dysfunction, reduced ejaculate volume, breast tenderness or enlargement, and, less commonly, mood changes. In trials, short-term side-effect rates were broadly similar between the two at standard doses. But there's an important difference in how long the drug stays in your body:
| Finasteride | Dutasteride | |
|---|---|---|
| Enzymes blocked | Type 2 | Types 1 and 2 |
| Blood DHT reduction | About 70% | About 90% or more |
| Half-life | Hours | About 5 weeks |
| U.S. approval for hair loss | Yes (1 mg) | No (off-label) |
Because dutasteride lingers for weeks, side effects don't disappear quickly if you stop. That's one reason many doctors start with finasteride. Some clinicians also prescribe topical dutasteride or dutasteride injected into the scalp ("mesotherapy"), though the evidence for those approaches is more limited.
Can I take both?
There's no good reason to, and no trials support combining them, since they work through the same pathway. Switching from one to the other is common; stacking them isn't.
Who shouldn't take either?
Women who are or may become pregnant should not take or handle crushed or broken tablets or leaking capsules, because these drugs can affect a male fetus. Men taking either drug should also know they lower PSA levels, which matters for prostate cancer screening, so tell any doctor who orders a PSA test. Dutasteride users are typically asked not to donate blood for at least six months after their last dose.
The bottom line
Finasteride is the approved, first-line option and works well for many men. Dutasteride is a stronger, longer-lasting alternative with good supporting evidence, best discussed with a dermatologist who can weigh your history, your goals and how you've responded so far. Either works only as long as you take it, and shampoos and other topicals are best seen as supporting care, not substitutes.
Scott Blaine Hoffman has worked in the hair-loss field for more than 30 years. This article is general information, not medical advice. Talk with your doctor before starting or changing any medication.