Saw Palmetto (Serenoa repens) is a small palm tree whose berries have been used in men's health formulas for decades, mostly in connection with prostate and urinary function.
How It's Thought to Work
Saw Palmetto contains compounds believed to reduce the activity of 5-alpha reductase, the enzyme responsible for converting testosterone into dihydrotestosterone (DHT). It may also affect how DHT binds to receptors in prostate cells, which is the basis for its traditional use in supporting prostate health.
Prostate Health Research
A well-known 1998 systematic review in JAMA, covering 18 randomized controlled trials and nearly 3,000 men, found that Saw Palmetto extract — taken for an average of nine weeks — was associated with improved urinary symptoms and peak urinary flow in men with benign prostatic hyperplasia (BPH), a common age-related prostate enlargement. Later studies using standardized symptom scores have reported similar improvements in symptoms like nocturia (nighttime urination), weak stream, and hesitancy.
Testosterone and Inflammation
Saw Palmetto is also studied for general anti-inflammatory properties and its role in regulating the testosterone-to-DHT conversion pathway, though researchers note more human trials are needed to confirm these effects specifically.
Where the evidence stands: Short-term studies show reasonably consistent benefit for urinary symptoms tied to BPH. Long-term studies and effects beyond prostate/urinary symptoms are more mixed, so it's best viewed as a traditional, moderately well-studied ingredient rather than a guaranteed fix.
Where It Shows Up
Saw Palmetto Berry Extract is one of the seven ingredients in HorseWood.
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View HorseWoodSources: Healthline, Rupa Health.