© Eric Yarnell, ND, Mar 2008, updated Feb 2013

Many patients have the concern that Serenoa repens (saw palmetto) extracts might interfere with the measurement of PSA and thus block a prostate cancer diagnosis. Many double-blind trials have shown no effect of saw palmetto on total PSA.

This was the conclusion of the authors of a systematic review of clinical trials on standardized extract of saw palmetto (Gerber and Fitzpatrick 2004). One of the largest trials ever conducted on saw palmetto extract, involving over 1,000 men, found no effect of the herb on PSA (Carraro, et al. 1996). A review of a smattering of high-quality clinical trials over the years, including the longest-running trial yet (at 24 months) confirms the lack of interference (Andriole, et al. 2013; Bent, et al. 2006; Djavan, et al. 2005; Marks, et al. 2001). So far I know of only one clinical trial that assessed the effect of saw palmetto on free PSA (Willetts, et al. 2003). No effect was noted compared to placebo.

The confusion over this issue comes from the fact that finasteride (Proscar) and dutasteride (Avodart) both artificially lower the total PSA reading by approximately 50% (Thompson, et al. 2007; Andriole, et al. 2006). While it is not known for sure why this occurs, I suspect it is because these drugs reduce the size of the prostate, and thus production of PSA by normal cells. They do not affect production by cancer cells.

A potentially critical difference between these drugs and saw palmetto is that, based on studies in humans, the drugs inhibit 5-alpha-reductase 80% compared to 32% for saw palmetto (Marks, et al. 2001). It is also likely that saw palmetto’s other actions besides inhibiting 5-alpha-reductase may contribute to its lack of falsely inhibiting PSA.

While saw palmetto was once just dismissed in mainstream medicine an inferior herbal version of these drugs, this is clearly not true. Saw palmetto works by many mechanisms and not just by blocking the 5-alpha-reductase enzyme as these drugs do, and is clearly just as effective as these drugs with vastly fewer adverse effects and for much less money (Gordon and Shaughnessy 2003).


Saw palmetto does not artificially interfere with measurement of total or free PSA.


Andriole GL, McCullum-Hill C, Sandhu GS, et al. (2013) “The effect of increasing doses of saw palmetto fruit extract on serum prostate specific antigen: analysis of the CAMUS randomized trial” J Urol 189(2):486-92.

Andriole GL, Marberger M, Roehrborn CG (2006) “Clinical usefulness of serum prostate specific antigen for the detection of prostate cancer is preserved in men receiving the dual 5alpha-reductase inhibitor dutasteride” J Urol 175(5):1657-62.

Bent S, Kane C, Shinohara K, et al. (2006) “Saw palmetto for benign prostatic hyperplasia” N Engl J Med 354:557-66.

Carraro JC, Raynaud JP, Koch G, et al. (1996) “Comparison of phytotherapy (Permixon®) with finasteride in the treatment of benign prostatic hyperplasia: A randomized international study of 1,098 patients” Prostate 29:231-40.

Djavan B, Fong YK, Chaudry A, et al. (2005) “Progression delay in men with mild symptoms of bladder outlet obstruction: A comparative study of phytotherapy and watchful waiting” World J Urol 23(4):253-6.

Gerber GS, Fitzpatrick JM (2004) “The role of a lipido-sterolic extract of Serenoa repens in the management of lower urinary tract symptoms associated with benign prostatic hyperplasia” BJU Int 94:338-44.

Gordon AE, Shaughnessy AF (2003) “Saw palmetto for prostate disorders” Am Fam Phys 67:1281-3.

Marks LS, Hess DL, Dorey FJ, et al. (2001) “Tissue effects of saw palmetto and finasteride: Use of biopsy cores for in situ quantification of prostatic androgens” Urology 57:999-1005.

Thompson IM, Pauler Ankerst D, Chi C, et al. (2007) “Prediction of prostate cancer for patients receiving finasteride: Results from the Prostate Cancer Prevention Trial” J Clin Oncol 25(21):3076-81.

Willetts KE, Clements MS, Champion S, Ehsman S (2003) “Serenoa repens extract for benign prostatic hyperplasia: A randomized controlled trial” BJU Int 92:267-70.