Treating symptoms of benign prostatic hyperplasia (BPH) in men who have an enlarged prostate gland. Dutasteride/tamsulosin is a 5 alpha-reductase inhibitor and alpha-blocker combination. The 5 alpha-reductase inhibitor (dutasteride) works by lowering levels of a hormone called dihydrotestosterone (DHT), which is a major cause of prostate growth. The alpha-blocker (tamsulosin) works by relaxing muscles in the prostate and bladder. Dutasteride/tamsulosin helps to decrease the size of the prostate and reduce symptoms of BPH.