Dutasteride is a 5-alpha reductase inhibitor that is more potent than finasteride — it inhibits both type I and type II 5-alpha reductase, compared to finasteride which inhibits only type II. This gives dutasteride a stronger effect on DHT reduction, and there is growing evidence that it produces better outcomes for hair loss than finasteride in many patients.
Finasteride at 1mg reduces serum DHT by approximately 70%. Dutasteride at 0.5mg — the standard dose for benign prostatic hyperplasia — reduces serum DHT by approximately 90 to 95%. This difference in DHT suppression translates to measurably better hair retention and regrowth in head-to-head comparison studies.
A randomised controlled trial comparing dutasteride 0.5mg to finasteride 1mg in men with androgenetic alopecia found statistically significantly greater improvements in hair count and patient satisfaction with dutasteride at twelve and twenty-four weeks. These results have been replicated in subsequent studies.
The trade-off is side effects. Dutasteride’s broader inhibition of both 5-alpha reductase isoforms means it reduces DHT more systemically than finasteride. The side effect profile is similar in type — sexual effects, mood effects in a small minority — but potentially with somewhat higher rates due to the greater systemic DHT reduction.
Dutasteride is not licensed for hair loss in the UK and is used off-label. It requires a private prescription and a discussion with a prescribing physician about the evidence, the off-label status, and the side effect profile. For patients who have not responded adequately to finasteride, dutasteride is a logical next step.
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