Are 5-Alpha-Reductase Inhibitors Safe to Take?

• Clinical Trial Evidence
• Finasteride and Dutasteride Safe to Treat Hair Loss?
• Sexual Side Effects

Finasteride is approved by the U.S. Food and Drug Administration (FDA) in 1-mg doses to treat hair loss in men with androgenic balding. Dermatologists have used dutasteride as an off-label hair loss treatment in doses up to 2.5-mg daily in men as well. Finasteride or dutasteride are not recommended for use in women because of the risk of serious birth defects, but both have been prescribed to treat hair loss in some women. However, women of child-bearing age should not use these drugs without contraception to prevent pregnancy.^{(13, 30, 199)}

Evidence from Clinical Trials Regarding Cancer Risk in Men

Long-term clinical trials have been conducted to measure the effects of 5-alpha-reductase inhibitors on reducing rates of prostate cancer. Some of the results have raised concern about links between these drugs and an increased risk of high-grade prostate cancer:⁽³⁾

Results of these 2 trials prompted the FDA to ask for new label warnings.⁽³⁾

Changes in Later Analysis of Clinical Trials

The researchers in both trials had concluded 5-alpha-reductase inhibitors could reduce the risk of low-grade prostate cancer by 23-25% overall. However, a later analysis of the data revised the rate of decrease down from 24.8% to 14%. Further, 80% of the rate of decrease was for very-low-risk prostate cancer. Clearly this meant the cancer-reducing benefits of finasteride were not as great as once thought.⁽²⁰¹⁾

This review also raised the slight increase in risk of high-grade prostate cancer (linked to the drugs) predicted by the earlier studies. As a result, the researchers advising the FDA suggested that these 5-alpha-reductase inhibitors not be used as drugs to prevent prostate cancer. Dutasteride is currently approved by the FDA in dosages of 0.5 mg/daily to treat benign prostate enlargement.^(29, 201)

Does the Clinical Evidence Suggest 5-Alpha-Reductase Inhibitors are Safe to Treat Hair Loss?

The dosage of finasteride used in the PCPT study was five times that generally prescribed to men with male pattern balding (5-mg vs. 1-mg daily). However, the dosage in the REDUCE clinical trial was 0.5 mg of dutasteride a day. This dose was up to five times less than the highest dose used in some hair loss studies. The possibility of increased risk for high-grade prostate tumors should be carefully considered before using 5-alpha-reductase inhibitor drugs—particularly those that block both types of the enzyme.^{(3, 9, 201)}

It's important to remember that 5-alpha-reductase inhibitors were originally developed (and are still used) to treat benign prostate hyperplasia (BPH), a common condition that causes prostate enlargement in older men. These drugs work to treat BPH by inhibiting one or both types of the 5-alpha-reductase enzyme in the prostate.⁽⁹⁵⁾

One of the side effects from these synthetic drugs is the lowering of PSA numbers, which are used as an indicator of prostate cancer. Men are urged to advise their doctor if they are using either finasteride or dutasteride so PSA values can be adjusted accordingly. It appears that the natural herb saw palmetto does not affect PSA values.^(95, 201)

Sexual Function Side Effects Reported in Men

Although relatively rare, side effects on sexual function have been reported in male patients using finasteride and dutasteride drugs. Higher dosages corresponded to increased chances of side effects.^(22, 30)

These side effects include:^(22, 30)

Interestingly, these side effects are not reported with saw palmetto. In fact, historically the herb has been used to treat sexual dysfunction in men.⁽⁹⁵⁾