Information and Solutions for Men and Women

Are 5-Alpha-Reductase Inhibitors Safe to Take?

Side effects and risk factors of certain hair loss drugs include increased risk of some cancers.

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.(1330199)

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)

Clinical Trial Name Trial Design Results
Prostate Cancer Prevention Trial (PCPT)
  • Multicenter; conducted at some of the leading cancer research centers in the United States.
  • Approximately 19,000 healthy male participants over age 54 assessed as low-risk for prostate cancer.
  • Patients given 5-mg of finasteride daily for up to seven years.
25% lower rate of prostate cancer overall, but a slight increase (6.4% vs. 5.1%) in rate of high-grade prostatic cancer.(200201)
Reduction by Dutasteride of Prostate Cancer Events (REDUCE) Trial
  • Randomized, blinded, and placebo-controlled 4-year clinical trial conducted at multiple centers throughout the United States; funded and designed by the drug company GlaxoSmithKline.

  • Over 6500 men between the ages of 50 and 75 and at high-risk for developing prostate cancer because of past clinical history (including PSA levels).

  • Patients were divided into almost equal-sized groups and randomly assigned to take either 0.5 mg/day of dutasteride or a placebo.

At the end of the 2nd and 4th year, needle biopsies were taken from all participants and analyzed for cancer. The overall prostate tumor rate was almost 23% lower in the dutasteride-treated group.(202)

However, during the final 2 years of the trial only 1 participant in the placebo group developed the highest grade of prostate cancer compared to 12 in the dutasteride group. In addition, the incidence of heart failure in the treated group was almost double that of those who took the placebo (30 vs. 16 men).(202)

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.(29201)

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.(39201)

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.(95201)

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.(2230)

These side effects include:(2230)

Decreased libido
Ejaculation disorders  
Erectile Dysfunction (ED)  

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)

Hair Regrowth is Possible
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Finasteride is rated category X by the FDA in terms of risk of birth defects, meaning the benefits do not outweigh known risks.(199)
More difficult to treat and with a worse prognosis.(201)
Published in 2011 in The New England Journal of Medicine.(201)
Revision based upon eliminating end-of-study biopsy results done on patients with non-elevated PSA or normal rectal examinations.(201)