In those who are being regularly screened, 5α-reductase inhibitors such as finasteride and dutasteride reduce the overall risk of being diagnosed with prostate cancer; however, there is insufficient data to determine if they have an effect on the risk of death and may increase the chance of more serious cases.
This class of medications increases rates of erectile dysfunction (with between 5% and 9% developing problems after starting their use). This is linked to lower quality of life and can cause stress in relationships. There is also an association with lowered sexual desire. It has been reported that these adverse sexual side effects may persist even after discontinuation of the drug.
The FDA has added a warning to dutasteride about an increased risk of high-grade prostate cancer. While the potential for positive, negative or neutral changes to the potential risk of developing prostate cancer with dutasteride has not been established, evidence has suggested it may temporarily reduce the growth and prevalence of benign prostate tumors, but could also mask the early detection of prostate cancer. The primary area for concern is for patients who may develop prostate cancer whilst taking dutasteride for benign prostatic hyperplasia, which in turn could delay diagnosis and early treatment of the prostate cancer, thereby potentially increasing the risk of these patients developing high-grade prostate cancer.
Children and women who are or may become pregnant, and people with known significant hypersensitivity (e.g., serious skin reactions, angioedema) to dutasteride or finasteride should not take dutasteride. Exposure to dutasteride and other 5α-reductase inhibitors during pregnancy can cause birth defects. Since these medications are readily absorbed through the skin, women who are or may become pregnant should not handle them and if they come into contact with leaking capsules, the contact area should be washed immediately in soapy water. People taking dutasteride should not donate blood and, due to its long half-life, should also not donate blood for at least 6 months after the cessation of treatment.
^ abYamana K, Labrie F, Luu-The V (January 2010). "Human type 3 5α-reductase is expressed in peripheral tissues at higher levels than types 1 and 2 and its activity is potently inhibited by finasteride and dutasteride". Hormone Molecular Biology and Clinical Investigation2 (3). doi:10.1515/hmbci.2010.035.
^ abcGur, S; Kadowitz, PJ; Hellstrom, WJ (January 2013). "Effects of 5-alpha reductase inhibitors on erectile function, sexual desire and ejaculation.". Expert opinion on drug safety12 (1): 81–90. doi:10.1517/14740338.2013.742885. PMID23173718.
^ abcTraish, AM; Hassani, J; Guay, AT; Zitzmann, M; Hansen, ML (March 2011). "Adverse side effects of 5α-reductase inhibitors therapy: persistent diminished libido and erectile dysfunction and depression in a subset of patients.". The journal of sexual medicine8 (3): 872–84. doi:10.1111/j.1743-6109.2010.02157.x. PMID21176115.