Dutasteride and finasteride are both 5-alpha-reductase (5AR) inhibitors. Both treatments work by inhibiting 5AR, the enzyme responsible for converting testosterone to dihydrotestosterone (DHT). DHT is the primary androgen in the prostate. It is a primary factor in the development and progression of benign prostatic hyperplasia (BPH) and other prostate diseases and is also a major cause of hair loss.
Dutasteride is a competitive inhibitor of both type-1 and type-2 isoenzymes of DHT, with 45-fold greater potency than finasteride against type-1 and type-2 isoenzymes. Approximately 85% to 90% of DHT is suppressed by the inhibition of type-2 isozymes. The remaining DHT is hypothesized to be from type-1 5-alpha-reductase. Finasteride is a competitive inhibitor of 5-alpha-reductase that selectively inhibits the type-2 isoenzyme. The dual inhibition resulting from dutasteride treatment may be beneficial for treat male pattern baldness better than Finasteride .