EBM Consult

How does saw palmetto (Serenoa repens) work to treat benign prostatic hyperplasia (BPH)?


  • Saw palmetto (Serenoa repens) is derived from the berry of the American dwarf tree found in the southern part of the United States and is widely used all over the world for the treatment of benign prostatic hyperplasia (BPH) symptoms.
  • A Cochrane Review in 2002 suggested that Serenoa repens provided mild to moderate improvement in urinary symptoms and flow measures when compared to placebo or finasteride.  However, the Saw palmetto for Treatment of Enlarged Prostates (STEP) trial in 2006 did not show a difference in standard or established outcomes.  Studies do consistently show that there do not appear to be major side effects.
  • Studies suggest that Serenoa repens is an inhibitor of both type 1 & 2 5a-reductases which are enzymes required for the conversion of testosterone to the more potent androgen 5a-dihydrotestosterone (DHT).  This is similar to current prescription products for BPH, dutasteride (Avodart) and finasteride (Proscar).

Editor-in-Chief: Anthony J. Busti, MD, PharmD, FNLA, FAHA

Last Reviewed: August 2017


  • Saw palmetto (Serenoa repens) is derived from the berry of the American dwarf tree found in the southern part of the United States and is widely used all over the world for the treatment of benign prostatic hyperplasia (BPH) symptoms.(1)  In fact, a survey of men in a urology clinic revealed that one third of respondents utilized herbal medicinals for their BPH and that their use continues to rise.(1,2)  Another analysis conducted in Italy showed that nearly half of the medications dispensed for BPH were for herbal medicines and in Germany and Austria herbal medicinals make up >90% of the prescriptions for BPH symptoms.(3) 

    Is there any evidence to support its widespread use?

    • In 2002, the Cochrane Collaboration published an extensive review on the efficacy and safety of Serenoa repens in the treatment of symptoms related to BPH.(1)  They assessed 3,139 men from 21 randomized trials lasting 48 weeks (18 were double blinded with 11 of those having adequate measures for concealment of treatment allocation).(1)  Compared to placebo, Serenoa repens provided mild to moderate improvement in urinary symptoms and flow measures.(1)  When compared to finasteride, a type 2 5a-reductase inhibitor available by prescription, Serenoa repens produced similar improvements and was associated with fewer adverse treatment events.(1)  
    • However, in 2006 the Saw palmetto for Treatment of Enlarged Prostates (STEP) trial, which was a randomized, double-blind clinical trial of 225 men with moderate-to-severe BPH symptoms, was published in the New England Journal of Medicine and revealed conflicting results.(4) 
    • Using currently accepted standards of clinical outcomes, this trial showed no differences in the American Urological Association Symptom Index (AUASI) score, maximal urinary flow, prostate size, residual volume after voiding, quality of life, or serum prostate-specific antigen levels between the saw palmetto and placebo groups.(4)  It has been suggested that the discrepancy between other studies and this trial may be an inconsistency in Serenoa repens preparations/dosage forms, lack of adequate blinding, and standard outcome measures in the older studies compared to those used in the STEP study.(1,4)  For example, in the STEP trial purity and potency testing by high-performance gas chromatography was performed on their Serenoa repens extract and verified that it met the standards set by the National Center for Complementary and Alternative Medicine.  Regardless, the current data shows that Serenoa repens is not harmful when used for up to one year.(1,4,5) 

    How does Serenoa repens work since some patients report an apparent improvement in BPH symptoms?

    • One of the primary causes of symptoms related to non-malignant prostatic hyperplasia is due to the influence of the potent androgen 5a-dihydrotestosterone (DHT) on prostate tissue.(6)  Testosterone produced by the body is converted to DHT in the prostate by the enzyme type 2 5a-reductase.  Type 1 5a-reductase is mainly involved in testosterone's conversion to DHT in the skin and liver.  Upon activation, DHT binds to androgen receptors that enter into the nucleus of prostatic cells causing an increase in gene transcription.  This increase results in the enlargement of the prostate tissue. 
    • Studies suggest that at least one mechanism of action for Serenoa repens is an inhibition of both type 1 & 2 5a-reductases.(7)  This is the same mechanism of action as the currently available prescription products. Dutasteride (Avodart) is also an inhibitor of both type 1 & 2 5-alpha-reductase while finasteride (Proscar), is a competitive inhibitor of only type 2 5a-reductase.(7-9)  Both dutasteride and finasteride are FDA approved for BPH.(8,9)  In addition, Serenoa repens is known to have antiandrogenic activity as well.(10)
    • Serenoa repens appears to improve symptoms of BPH in some patients though the clinical trial evidence to support this is conflicting and debated.  As with prescription medications (dutasteride and finasteride), the maximal benefit on symptoms may take 2 weeks to 3 months to realize.(8,9)   The more common side effects reported in the literature were impotence in 1.1% of men and gastrointestinal side effects in 1.3% and may be related to the formulation used.(1,11)  There are numerous formulations available with brand, Permixon®, being one of the more common forms studied.(11)  The U.S. Pharmacopeia indicates that a Serenoa repens extract product should be made of 70 to 95% fatty acids and 0.2 to 0.5% sterols.(12)


    1. Wilt T, Ishani A, Stark G et al.  Serenoa repens for benign prostatic hyperplasia (Cochrane review).  Cochrane Database Syst Rev   2002;(3):CD001423.
    2. Bales GT, Christiano AP, Kirsh EJ et al.  Phytotherapeutic agents in the treatment of lower urinary tract symptoms: a demographic analysis of awareness and use at the University of Chicago.  Urology  1999;54(1):86-9.      
    3. Di Silverio F, Flammia GP, Sciarra A et al.  Plant extracts in BPH. Minerva urol Nefrol  1993;45(4):143-9.       
    4. Bent S, Kane C, Shinohara K et al.  Saw palmetto for benign prostatic hyperplasia.  N Engl J Med 2006;354:557-66.       
    5. Avins AL, Bent S, Staccone S et al.  A detailed safety assessment of a saw palmetto extract.  Complement Ther Med  2008;16(3):147-54.      
    6. Bruchovsky N, Wilson JD.  The intranuclear binding of testosterone and 5-alpha-androstan-17-beta-ol-3-one by rat prostate.  J Biol Chem  1968;243:5953-5960.      
    7. Iehle C, Delos S, Guirou O et al.  Human prostatic steroid 5 alpha-reductase isoforms - a comparative study of selective inhibitors.  J Steroid Biochem Mol Biol   1995;54(5-6):273-9.
    8. GlascoSmithKline.  Avodart (dustasteride) product insert.  Research Triangle Park, NC. June 2008.
    9. Merck & Co, Inc. Proscar (finasteride) product insert.  Whitehouse Station, NJ.  March 2007. 
    10. Ravenna L, Di Silverio F, Russo MA et al.  Effects of the lipidosterolic extract of Serenoa repens (Permixon) on human prostatic cell lines.  Prostate  1996;29(4):219-30.
    11. Fagelman E, Lowe FC.  Saw Palmetto Berry as a Treatment for BPH.  Rev Urol   2001;3(3):134-8. 
    12. Saw palmetto extract.  In: Expert Committee.  United State pharmacopeial forum: (DSB) dietary supplements: botanicals. Vol 28. No.2. Rockville, Md.: Pharmacopeial Convention, 2005:425. (USP28-NF23).



  • Saw Palmetto, BPH, Serenoa repens, Saw Palmetto Prostate, Herbal Supplement BPH