Dutasteride
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 | Countermeasures |
|---|---|---|---|---|
| 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 Commonly used with
What dutasteride is combined with, and why. This is about intent rather than safety — the interactions table below covers what is dangerous. Nothing here is listed without what it costs.
| Compound | Frequency | Purpose & trade-off |
|---|---|---|
| Support & ancillaries | ||
| Testosteronehair protection | Chosen over finasteride with testosterone for near-complete DHT suppression to protect the hairline.Trade-off: Its dual-isoenzyme blockade and long half-life amplify sexual, mood and possible metabolic side effects. | |
| Finasterideescalation | Represents the stronger step up when finasteride alone fails to control androgenic hair loss.Trade-off: Deeper, longer-lasting DHT suppression means side effects persist well after discontinuation. | |
| Testosterone Propionateprostate/scalp | Used to hold down DHT-mediated scalp and prostate effects during androgen use.Trade-off: Very low DHT can reduce libido, erectile quality and the sense of drive androgens usually give. | |
| Minoxidiltopical adjunct | Combined with topical minoxidil to attack androgenic hair loss from both hormonal and vascular angles.Trade-off: Minoxidil requires indefinite use and can cause shedding and irritation, while dutasteride's systemic sides remain. | |