Ancillary5-alpha-reductase inhibitorDual inhibitorAncillary

Dutasteride

Also known as Avodart · Dut

Written by enwyReviewed 4 Aug 20262 sources0 comments

Dutasteride is a dual (type I and type II) 5-alpha-reductase inhibitor, more complete and longer-acting than finasteride. It suppresses serum DHT by more than 90%, making it a stronger option for DHT-driven hair loss and BPH — with correspondingly greater potential for DHT-dependent sexual side effects and a very long half-life that means effects persist for weeks after stopping.

01 Overview

Dutasteride blocks both isoforms of 5-alpha-reductase, whereas finasteride blocks mainly type II. This produces greater DHT suppression — over 90% of serum DHT versus roughly 70% for finasteride — and a stronger effect on androgenetic hair loss and prostate volume. Like finasteride, it only addresses DHT-mediated effects and offers no benefit against non-5AR-substrate androgens.

The cost of that potency is a similar but potentially more pronounced side-effect profile and an extremely long elimination half-life (around five weeks), so DHT stays suppressed and any adverse effects can linger long after the last dose. It likewise roughly halves PSA and must be flagged in prostate screening.

02 Mechanism

Dual inhibitor of type I and type II 5-alpha-reductase, reducing serum DHT by over 90%.

03 Dosing

Tier	Dose	Route	Notes
BPH / hair loss	0.5 mg/day	Oral	Standard 0.5 mg/day; some use it less frequently for hair given the long half-life.

04 Effects

Effect	Magnitude	Evidence
Profound DHT suppressionSuppresses DHT more completely than finasteride, giving stronger effect on DHT-driven hair loss.	>-90% serum DHT	Clinical
Prostate shrinkageReduces prostate size and urinary symptoms in BPH, comparable to or greater than finasteride.	reduced volume	Clinical

05 Side effects

Effect	Severity	Frequency	Evidence
Sexual dysfunctionReduced libido, erectile dysfunction and ejaculatory changes; because of the long half-life, effects can persist for weeks after stopping.	Moderate	Uncommon	Clinical
Lowered PSA (screening confound)Roughly halves serum PSA, confounding prostate cancer screening.	Moderate	Universal	Clinical
No protection vs non-DHT androgensOnly DHT-mediated hair loss responds; non-5AR-substrate androgens are unaffected.	Moderate	Inherent limitation	Clinical

06 Legal status

United States

Prescription drug (Rx)

Approved as Avodart for BPH; hair-loss use is off-label in the US (approved for hair loss in some countries). · as of Jan 2026

United Kingdom

POM

as of Jan 2026

07 References

Dutasteride versus finasteride: DHT suppression and efficacyJ Clin Endocrinol Metab / J Am Acad Dermatol

Avodart (dutasteride) FDA labelUS FDA

08 Discussion0 comments

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This page is reference information, not medical advice. Doses and protocols are documented as they appear in the clinical literature and in practice — describing them is not a recommendation to use them. Countermeasures listed here are not a substitute for a physician. Legal status varies by jurisdiction and changes.