There's reason to suspect that saw palmetto might affect prostate specific antigen (PSA) levels, but to date we have little scientific evidence that this herbal remedy interferes with the commonly used cancer screening blood test.
The extract of the saw palmetto plant (Serenoa repens) is often recommended for disorders of the prostate gland. Medical studies have reached different conclusions about this remedy's effectiveness, but most experts believe that saw palmetto is a safe and reasonably effective treatment, particularly for benign prostatic hyperplasia (BPH).
Very little is known about how and why saw palmetto is useful for prostate conditions. Some research suggests that the extract blocks the effects of testosterone within the prostate, much like the drug finasteride (Proscar). Finasteride, in turn, can lower blood levels of PSA. Since PSA is often used to screen for prostate cancer, men who take finasteride for prostate conditions are often warned that their PSA levels may not be accurate for detecting early stage cancers.
However, there's been little to no research looking at how saw palmetto affects PSA levels. A single study that compared finasteride and saw palmetto for chronic prostatitis found that saw palmetto had slightly less impact on PSA levels. That said, it's impossible to know whether doctors should use a different PSA cut-off in men taking the herbal extract. There's also some question as to whether saw palmetto might actually help to prevent prostate cancer, although there's been little research on this connection, either.
Bottom line: Men who are thinking about long-term treatment with saw palmetto should consult with their doctor. It may make sense to check a PSA level before starting the drug. However, it's unlikely that taking saw palmetto will lead to wildly inaccurate PSA results, or a missed diagnosis of prostate cancer.
