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5-Alpha Reductase Inhibitors for Benign Prostatic Hyperplasia


Generic NameBrand Name
dutasterideAvodart, Proscar
finasterideAvodart, Proscar

How It Works

5-alpha reductase inhibitors interfere with the effect of certain male hormones (androgens) on the prostate. This slows the growth of the prostate and can even cause it to become smaller, which may help improve the symptoms of benign prostatic hyperplasia (BPH).

But since prostate size does not always correspond to the severity of a man's symptoms, these medicines will not give satisfactory results in every case.

When you stop taking the medicine, symptoms usually return.

Why It Is Used

5-alpha reductase inhibitors are not recommended for men who have BPH symptoms without a noticeably enlarged prostate. 5-alpha reductase inhibitors may be prescribed for men who have bothersome, moderate symptoms of BPH.

How Well It Works

Most men who use 5-alpha reductase inhibitors report about a 3-point decrease in their American Urologic Association (AUA) symptom index. This change represents a noticeable improvement in symptoms.1 5-alpha reductase inhibitors also decrease the risk of complications, such as being unable to urinate (urinary retention), and make it less likely that you will need surgery.2

It may take 6 to 12 months before symptom improvement is noticeable.

Using a combination of an alpha-blocker with a 5-alpha reductase inhibitor may help your symptoms more than either medicine alone.3

Side Effects

Side effects may include:

  • Decreased sex drive.
  • Increased ejaculatory dysfunction (such as a smaller amount of semen ejaculated).
  • Difficulty getting an erection.
  • Breast tenderness or enlargement.

These side effects may go away after a year or more of taking the medicine.

It is possible that 5-alpha reductase inhibitors are linked to an increased risk for high-grade prostate cancers. But more research is needed.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

5-alpha reductase inhibitors reduce the size of the prostate. But since a reduction in size does not always bring about symptom relief, these medicines will not give satisfactory results in every case. When you stop taking the medicine, symptoms usually return.

5-alpha reductase inhibitors lower prostate-specific antigen (PSA) levels. Because PSA levels are used to detect early-stage prostate cancer, men interested in taking a 5-alpha reductase inhibitor might consider the following:

  • Most experts suggest that men be checked for the presence of prostate cancer (using the PSA test and a digital rectal exam) before taking 5-alpha reductase inhibitors.
  • Follow-up PSA levels that have not decreased by approximately 50% after 6 months of taking a 5-alpha reductase inhibitor may indicate a need for further testing for prostate cancer.
  • PSA levels above 2 ng/mL (nanograms per milliliter) during 5-alpha reductase inhibitor treatment may indicate a need for further testing for prostate cancer.

5-alpha reductase inhibitors are not recommended for treatment of BPH symptoms in men who do not have an enlarged prostate.1

The medicine must be taken for the rest of your life to prevent the symptoms from returning.

This medicine should not be used by men who plan to father a child, because there is a small chance that the medicine could cause a birth defect. Women who are pregnant or might become pregnant should not handle broken or crushed tablets of finasteride or dutasteride.

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  1. AUA Practice Guidelines Committee (2003). AUA guideline on management of benign prostatic hyperplasia (2003). Chapter 1: Diagnosis and treatment recommendations. Journal of Urology, 170(2, Part 1): 530–547. Available online:

  2. Webber R (2006). Benign prostatic hyperplasia, search date May 2005. Online version of BMJ Clinical Evidence. Also available online:

  3. Roehrborn CG, et al. (2008). The effects of dutasteride, tamsulosin and combination therapy on lower urinary tract symptoms in men with benign prostatic hyperplasia and prostatic enlargement: 2-year results from the CombAT study. Journal of Urology, 179(2): 616–621.


ByHealthwise Staff
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerChristopher G. Wood, MD, FACS - Urology, Oncology
Last RevisedAugust 23, 2011

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