Thinning Hair
Thinning Hair

No one can stop hair loss completely. But you can have healthier, fuller and thicker hair while slowing down the rate of loss.

Are 5α-Reductase Inhibitors Safe to Take?

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

Lengthy randomized, placebo-controlled clinical trials to assess the effects of 5α-reductase inhibitors on reducing rates of prostate cancer have provided valuable information on their safety in men. Some of the results have raised concern about the use of these drugs and increased risk of high-grade prostate cancer, which has prompted the FDA to ask for new label warnings:3

  • Prostate Cancer Prevention Trial (PCPT). This clinical trial was conducted at some of the leading cancer research centers in the United States and involved almost 19,000 healthy men over age 54 assessed as low-risk for the disease. They were given 5-mg of finasteride daily for up to seven years. The original results suggested a 25% lower rate of prostate cancer overall, but a slight increase (6.4% vs. 5.1%) in rate of high-grade prostatic cancer.200-201
  • Reduction by Dutasteride of Prostate Cancer Events (REDUCE) trial. Funded and designed by the pharmaceutical company GlaxoSmithKline, this randomized, blinded, and placebo-controlled clinical trial assessed the effects of 0.5 mg/day of dutasteride in over 3,300 men against an almost equal-sized group who received a placebo instead. All participants were considered high-risk for developing prostate cancer because of past clinical history (including PSA levels) and were between the ages of 50 and 75. The four year study was conducted at multiple centers throughout the United States, and at the end of the second and fourth 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. However, during the final two years of the trial only one participant in the placebo group developed the highest grade of prostate cancer compared to twelve 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

Although the researchers in both trials had concluded 5α-reductase inhibitors could reduce the risk of low-grade prostate cancer by 23-25% overall, a later analysis of the finasteride data revised the rate of decrease in low-grade prostate cancer was to 14% from the 24.8% originally reported. Further, 80% of the rate of decrease was for very-low-risk prostate cancer.201

This review also raised the slight increase in risk of high-grade prostate cancer predicted by the earlier finasteride and dutasteride studies. In the final analysis, the researchers from an advisory panel to the United States Food and Drug Administration (FDA) suggested that these 5α-reductase inhibitors not be used as drugs to prevent prostate cancer, because of the increased risk of high-grade disease.201 Dutasteride is currently approved by the FDA in dosages of 0.5 mg/daily to treat benign prostate enlargement.29

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

Although the dosage used in the PCPT finasteride study was five times that generally prescribed to men with male pattern balding (5-mg vs. 1-mg daily), the dosage in the REDUCE dutasteride clinical trial was 0.5 mg a day—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 5α-reductase inhibitor drugs, particularly those that block both types of the enzyme.3, 192, 201

It's important to remember that 5α-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 5α-reductase enzyme in the prostate.96

One of the side effects from these synthetic drugs, however, 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 saw palmetto does not affect PSA values.96, 201

Sexual Function Side Effects Reported in Men

Although relatively rare, other dose-dependent adverse side effects on sexual function have been reported in male patients using finasteride and dutasteride. These include:22, 30

Decreased libido
Ejaculation disorders
Erectile Dysfunction (ED)

Table 39: Side Effects on Sexual Function from 5α-Reductase Inhibitors

Interestingly, these side effects are not reported with saw palmetto. In fact, historically the herb has been used to treat sexual dysfunction in men.96

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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.
More difficult to treat and with a worse prognosis.
Revision based upon eliminating end-of-study biopsy results done on patients with non-elevated PSA or normal rectal examinations.
Published in 2011 in The New England Journal of Medicine.
Higher dosages corresponded to increased chances of side effects.