Dutasteride is FDA-approved for bph/">benign prostatic hyperplasia only; using it for hair loss is off-label. Taking dutasteride and finasteride together is generally not recommended by clinicians. Both drugs are 5-alpha reductase inhibitors that target the same enzymatic pathway. Because dutasteride already blocks both Type 1 and Type 2 isoforms (which finasteride targets only Type 2 of), adding finasteride provides no meaningful additional DHT suppression and may increase the risk of side effects without added benefit.
Why There Is No Benefit
Dutasteride alone reduces serum DHT by approximately 94% by blocking both Type 1 and Type 2 5-alpha reductase; the Avodart label reports a median serum DHT decrease of 94% at 1 year on 0.5 mg/day. Finasteride blocks only Type 2: the Propecia label reports 65% suppression within 24 hours of a 1 mg tablet, and the Proscar label reports approximately 70% on 5 mg/day. Since dutasteride already covers all the enzymatic activity that finasteride targets (and more), adding finasteride cannot reduce DHT further.
Switching Between the Two
Switching from finasteride to dutasteride is common for patients who had an insufficient response. When switching, no washout period is typically needed. When switching from dutasteride to finasteride (less common), dutasteride’s long half-life means it will persist for months.
Dutasteride vs finasteride comparison · Dutasteride + minoxidil (recommended combination)
Sources
- Clark RV, et al. Marked suppression of dihydrotestosterone in men with benign prostatic hyperplasia by dutasteride, a dual 5alpha-reductase inhibitor. J Clin Endocrinol Metab. 2004;89(5):2179-84. PubMed
- FDA. Proscar (finasteride) prescribing information. DailyMed
- FDA. Avodart prescribing information. accessdata.fda.gov