Saw Palmetto (Serenoa repens): A Comprehensive Reference
1. Identity and Botanical Description
Botanical and Scientific Classification
Saw palmetto, botanically known as Serenoa repens, is a small palm native to the southeastern United States, known for its dark berries and saw-like leaves. It is also known under several synonymous names and trade designations, including American dwarf palm tree, cabbage palm, dwarf palm, sabal fructus, sabal serrulata, and serenoa serrulata.
The saw palmetto is native to the southeastern United States, with dense populations throughout Florida, South Georgia, and parts of South Carolina, Alabama, and Mississippi. With a low-growing, shrubby form and sharply serrated leaf stems—hence the name "saw" palmetto—this plant is perfectly adapted to survive fire, drought, and nutrient-poor soils. Some colonies of saw palmetto are believed to be thousands of years old, making them among the oldest living plant organisms in the world.
Currently, the majority of saw palmetto used commercially is obtained from the southern coastal United States. It should be noted that the chemical profile of any plant may vary substantially if it is collected from a significantly different environment.
Plant Part Used
The plant part typically used in dietary supplements is the fruit. This small, low-growing palm is distinguished by its dense clusters of serrated, fan-shaped leaves and its dark red berries, which are highly valued for their medicinal properties.
Common Forms and Preparations
A primary form of saw palmetto currently marketed is an n-hexane extract of the fruit, which is rich in lipids. Other forms include ethanol extracts of the fruit and powdered dried, ripe fruit. Saw palmetto is widely available as a supplement in capsule, soft gel, and tablet form. The most common supplement form is oily extracts of the fatty portions of the dried berries, as these provide higher levels of beneficial plant compounds than the raw fruit.
There are two primary forms of saw palmetto products in North America: saw palmetto extract, which is high in fatty acids; and saw palmetto ground berry powder, which is low in fatty acids. The presence of fatty acids is considered important since prostate cells preferentially take up fatty acids and sterols. Extracts are often standardized to 85–95% fatty acids by weight.
The saw palmetto berry has been used to make a tea or infusion, dried and ground to a powder, or to obtain an oil extract. There are also blended products that include saw palmetto as one ingredient in a sometimes complex mixture of botanical or other ingredients.
2. Traditional and Historical Use
Native American Traditions
In American Indian cultures, specifically in Florida, saw palmetto fruit was considered useful as a diuretic, sedative, aphrodisiac, nutritional tonic (due to the high oil content of the fruit), and to create a soothing vapor used as an expectorant. Native tribes of Florida such as the Seminoles relied on saw palmetto berries for food, and the Mayans drank it as a tonic; however, Europeans often found the taste of the berries objectionable.
Saw palmetto has a long history of use by Native Americans in treating bladder inflammation, urinary difficulties, sexual difficulties, and respiratory tract infections. Native American medicine men also reputedly kept saw palmetto to make antiseptic preparations and tonics, and to treat a wide variety of conditions, including impotence, inflammation, and infertility, and as an expectorant.
The Seminoles ground the berries into a nutritious flour. They also made an infusion from the berries to cure stomachaches and dysentery. The inner bark of the trunk was used as a packing on snake bites, insect bites, and skin ulcers.
Historical use of saw palmetto for symptoms of benign prostatic hyperplasia (BPH) has been common in Asia and in native cultures in North America for centuries. Of the 30 plants known to have been used historically in phytotherapy for symptoms of BPH, saw palmetto has been the most widely used.
Early American and European Medical Use
Native Americans in the southeastern United States have used saw palmetto since the 1700s to treat male urinary problems. In the 1800s, medical botanist John Lloyd noted that animals that ate saw palmetto appeared healthier and fatter than other livestock. Early American settlers noticed the same effects and used the juice from saw palmetto berries to gain weight, to improve general disposition, as a sedative, and to promote reproductive health.
It wasn't until the late 19th and early 20th centuries that saw palmetto gained wider recognition in the medical community. Doctors began prescribing saw palmetto extracts for prostate problems and other conditions, leading to increased demand for the plant's berries. Saw palmetto fell out of widespread use in North America at the start of the modern pharmaceutical era in the 1920s, though physicians in Europe continued prescribing it.
Historical uses were limited to saw palmetto in the form of the whole fruit, teas, aqueous extracts, and tinctures. They did not include lipid/sterol extracts of saw palmetto fruit such as those available in the current market.
Extracts of saw palmetto berries are commonly used in dietary supplement products in the United States, and phytomedicines in Europe and elsewhere, with a common usage being for benign prostatic hyperplasia. The berries rank in the top 13 herbal dietary supplement products in both mainstream and retail channels.
3. Key Constituents and Active Compounds
Lipid Fraction
Fixed oils represent approximately 26.7% of the composition. These include many free fatty acids and their glycerides, monoacylglycerides (1-monolaurin, 1-monomyristicin), as well as oleic acid (unsaturated) and capric acid, caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, and stearic acid (saturated).
Steroids include β-sitosterol, campesterol, stigmasterol, and other compounds. Different phytosterols include beta-sitosterol, stigmasterol, cycloartenol, lupeol, lupenone, campesterol, and 24-methyl-cycloartenol.
Other Constituents
In addition to lipids, other known chemical components of saw palmetto fruit include flavonoids, polyisoprenoids, and saccharides. Flavonoids present include rutin, isoquercitrin, and kaempferol. Other constituents include a pigment (carotene), resin, tannin, and volatile oil (approximately 1.5%). Other constituents include aliphatic alcohols (C26–30), polyprenic compounds, glucose, galactose, arabinose, uronic acid, and other polysaccharides.
Carbohydrates include invert sugar (approximately 28.2%), mannitol, and high molecular weight polysaccharides with galactose, arabinose, and uronic acid as main sugar components.
Standardization and Identity of Actives
The identity of the biologically active constituents has not been firmly established. Preparations of saw palmetto powdered fruit and saw palmetto extracts are typically analyzed for fatty acid content. Of the chemical constituents known to be present in saw palmetto fruit, none are recognized as toxic substances.
In comparing the in vitro potency of various brands of saw palmetto extract, all extracts tested were able to inhibit both isoforms of 5α-reductase to one degree or another. The potency of the extracts, as well as the potencies of two different batches of the same extract, appeared to be very different. This underscores the challenge posed by inter-batch variability in botanical preparations.
4. Proposed Mechanisms of Action
5α-Reductase Inhibition
Numerous mechanisms of action have been proposed for saw palmetto extract (SPE), including the inhibition of 5α-reductase. Previous studies have demonstrated that SPE has a number of pharmacological effects: (1) an anti-androgenic effect—inhibition of 5α-reductase I and II and inhibition of binding of dihydrotestosterone (DHT) to the cytosolic androgen receptors; (2) an anti-inflammatory effect; (3) an anti-proliferative effect; and (4) significant binding of pharmacological receptors existing in the lower urinary tract.
The nicotinamide adenine dinucleotide phosphate-dependent membrane protein 5α-reductase catalyses the conversion of testosterone to the most potent androgen, 5α-dihydrotestosterone. Two 5α-reductase isoenzymes are expressed in humans: type I and type II. The latter is found primarily in prostate tissue.
Saw palmetto's fatty acid constituents can directly inhibit enzymatic activities; for example, the saturated fatty acid lauric acid inhibits 5-alpha reductase of type I and II, whereas the monounsaturated fatty acid oleic acid inhibits 5-alpha reductase of type I.
Studies with a liposterolic extract of saw palmetto berries showed that it reduced tissue uptake of both testosterone and dihydrotestosterone (DHT) by more than 40%, suggesting antiandrogenic activity. Further, the extract inhibited binding of DHT to its receptor and blocked conversion of testosterone to DHT by inhibiting 5-alpha-reductase activity. However, in vitro studies suggest these antiandrogenic effects on 5α-reductase isoenzymes have not been paralleled by any clinical studies showing a decrease in serum dihydrotestosterone or prostate-specific antigen.
Anti-Inflammatory Effects
The berries also inhibit cyclooxygenase and 5-lipoxygenase pathways, thereby preventing the biosynthesis of inflammation-producing prostaglandins and leukotrienes.
Receptor Binding in the Lower Urinary Tract
Alpha(1)-adrenoceptor antagonists and muscarinic cholinoceptor antagonists are commonly used in the treatment of men with voiding symptoms secondary to BPH. The improvement of voiding symptoms in patients taking SPE may arise from its binding to pharmacologically relevant receptors in the lower urinary tract, such as alpha(1)-adrenoceptors, muscarinic cholinoceptors, 1,4-dihydropyridine receptors, and vanilloid receptors.
Anti-Proliferative Effects
In recent publications, it has been postulated that the liposterolic extract of S. repens has antiandrogenic effects, inhibits the type 1 and type 2 isoenzyme of 5α-reductase, inhibits prolactin and growth factor-induced cell proliferation, and has antiestrogenic and anti-inflammatory effects.
A variety of mechanisms for saw palmetto have been proposed including anti-androgenic, anti-inflammatory, and anti-proliferative effects, but none have been conclusively proven.
5. Scientific Evidence by Area of Use
5.1 Benign Prostatic Hyperplasia (BPH) and Lower Urinary Tract Symptoms (LUTS)
Saw palmetto is promoted as a dietary supplement for urinary symptoms associated with an enlarged prostate gland (also called benign prostatic hyperplasia or BPH), as well as for male pattern baldness, chronic prostatitis/chronic pelvic pain syndrome, and other conditions.
Overall Evidence Assessment
A 2023 review of 27 studies on saw palmetto in men with BPH found that this herb, when administered alone, provides little or no benefit for BPH symptoms. Definite conclusions could not be reached about the effects of combinations of herbs that include saw palmetto.
Although several small studies have suggested modest benefit of saw palmetto for treating symptoms of BPH, a large study evaluating high doses of saw palmetto and a Cochrane review found that saw palmetto was not more effective than placebo for treatment of urinary symptoms related to BPH.
There is a divergence between North American and European guidelines: North American guidelines state that "the available data do not suggest that saw palmetto has a clinically meaningful effect on LUTS secondary to BPH," while the European guidelines recommend using saw palmetto on the "basis of its long-standing use."
Key Clinical Trials
The largest trial was the Saw Palmetto Treatment for Enlarged Prostates (STEP) study. Two hundred twenty-five men aged ≥50 years with baseline symptom scores ≥8 were randomized to saw palmetto extract 160 mg twice daily or placebo. No improvement over placebo was found over one year in symptom scores or any secondary endpoints. No important toxicity was observed.
A 2012 Cochrane review of 32 randomized controlled trials involving 5,666 men with BPH found that Serenoa repens, at 2 and 3 times the usual dose, provides no improvement in urinary flow measures or prostate size in men with lower urinary tract symptoms consistent with BPH. Two clinical trials funded by the National Institutes of Health, both of which evaluated saw palmetto alone, were included in this review. One tested a standard dose of saw palmetto; the other tested increasing doses of saw palmetto, up to three times the usual dose. In both studies, saw palmetto did not improve BPH symptoms.
A study of 46 men published in 2024 found 320 mg/day for 12 weeks slightly decreased LUTS severity, but only in a clinically meaningful way among those with moderate symptoms (average decrease of 3 IPSS points).
A double-blind, placebo-controlled study found that daily intake of 320 mg SPE for 24 weeks significantly improved peak urinary flow and International Prostate Symptom Score (IPSS), as well as quality of life, and appeared to be an effective and well-tolerated therapeutic option in the target LUTS/BPH population.
Combination Therapy
A 2014 randomized trial of 225 men with lower urinary tract symptoms and BPH examined the efficacy and tolerability of combination therapy between saw palmetto, lycopene, and selenium plus tamsulosin versus single therapies. The findings suggest that a combination therapy of saw palmetto, lycopene, selenium, and tamsulosin is more effective than single therapies in improving International Prostate Symptom Score and increasing maximum urinary flow rate. After 6 months of treatment, the combination therapy significantly improved symptom scores compared with single therapy, and from 6 to 12 months, combination therapy demonstrated significant improvement in urine flow rate compared to tamsulosin alone. There were no reported treatment-related adverse events associated with combination therapy.
There is also some limited evidence that a combination of Urtica dioica (stinging nettle) and saw palmetto may be efficacious for lower urinary tract symptoms associated with BPH.
Effect on PSA Levels
In a large study, a saw palmetto extract did not affect serum prostate-specific antigen (PSA) more than placebo, even at high doses. By definitively establishing the lack of an effect on PSA by saw palmetto, even at supra-standard doses, this finding confirms that clinicians need not adjust serum PSA levels in men taking this herbal supplement who opt to undergo testing for prostate cancer early detection.
Pre-Surgical Evidence
Pretreatment with saw palmetto reduced intra- and postoperative complications in patients who underwent transurethral resection of the prostate and open prostatectomy, and reduced prostatic inflammation. This finding is preliminary and limited to a small evidence base.
5.2 Chronic Prostatitis / Chronic Pelvic Pain Syndrome (CP/CPPS)
A 2022 review of five studies on saw palmetto for chronic prostatitis/chronic pelvic pain syndrome did not find a significant benefit of the herb in patients with this condition. However, a more recent and larger systematic review presents a somewhat different picture.
Of 259 references, 21 studies encompassing 1,666 patients were selected. These studies included a range of trial types, with a mean follow-up period of approximately 6.975 months. Saw palmetto extract showed improved symptom relief compared with placebo, with mixed results when compared with alpha-blockers or 5-ARIs. Multimodal treatments, especially those including saw palmetto extract alongside antibiotics, displayed better efficacy in managing both Category II and Category III prostatitis. The authors concluded that saw palmetto extract provides symptom relief in patients with chronic prostatitis.
Some data also suggest benefits against chronic prostatitis/chronic pelvic pain syndrome. Overall, the evidence in this area is mixed, drawn from heterogeneous trials, and must be characterized as preliminary.
5.3 Androgenetic Alopecia (Hair Loss)
Saw palmetto, a botanical extract with antiandrogenic properties, has gained commercial popularity for its purported benefits on hair regrowth. Evidence on the efficacy, safety, and tolerability of supplements containing saw palmetto in the treatment of alopecia has been reviewed using PubMed, Google Scholar, and Cochrane database searches.
It is thought to work in hair loss by inhibiting the enzyme 5-alpha reductase, thereby reducing levels of DHT, the hormone that miniaturises hair follicles. While saw palmetto can decrease DHT by approximately 25 to 35 percent, as opposed to 60 to 70 percent with finasteride, the majority of clinical research indicates that it provides only slight advantages in improving hair growth among men with early stages of androgenetic alopecia, and these results are significantly weaker than those obtained with prescribed medications.
Several studies have demonstrated the effectiveness of Serenoa repens formulations for treating hair loss, but only assessed the treatment of male androgenetic alopecia. Two studies assessing the use of Serenoa repens included female subjects; however, both used oral formulations and combined Serenoa repens with other botanicals.
A 16-week, double-blind, placebo-controlled, four-arm clinical study assessed the safety and efficacy of VISPO™, a standardized saw palmetto oil (2–3% β-sitosterol), in subjects with mild-to-moderate androgenetic alopecia. Eighty healthy male and female subjects aged 18–50 years were randomly allocated (1:1:1:1) to receive either 400 mg capsules of VISPO or 5 mL of a topical formulation containing 20% VISPO or the respective placebo once daily for 16 weeks.
A few small studies have tested saw palmetto, used orally or topically (applied to the scalp), for male-pattern hair loss. The evidence is too limited to allow conclusions to be reached.
A head-to-head trial found finasteride produced superior outcomes in hair density, and finasteride is a licensed prescription medicine recommended as first-line for eligible men. Evidence for saw palmetto in female hair loss is even more limited than in men.
5.4 Prostate Cancer
A saw palmetto extract was found to inhibit growth of normal prostate cells and increase their sensitivity to radiation in vitro, but did not affect malignant prostate cancer cells. There is currently no reliable clinical evidence that saw palmetto prevents prostate cancer. It is researched specifically for benign (non-cancerous) prostate conditions and urinary symptoms. Evidence in this area is limited to preclinical (in vitro) findings only.
5.5 Other Areas Under Investigation
Apart from androgenetic alopecia, oral or topical saw palmetto has been evaluated for use in other hair and skin disorders such as telogen effluvium, seborrheic dermatitis, and reduction of facial sebum. These investigations are at early or pilot-study stages, and no definitive clinical conclusions have been established.
6. Dosage and Forms Reported in Studies
Standard Clinical Dose
The typical daily amount ingested (usually by men with benign prostatic hyperplasia) is 320 mg of lipid/sterol extract of saw palmetto (LESP). Most research uses saw palmetto at a daily dose of 320 mg, often divided into 2 doses.
Dose Escalation Studies
In the CAMUS dose-escalation randomized trial, participants received one, two, and then three 320 mg daily doses of saw palmetto extract or placebo, with dose increases at 24 and 48 weeks. The primary outcome was the difference in symptom score from baseline to 72 weeks. No benefit over placebo was found at any dose level in that study.
Hair Loss Studies
A 16-week clinical study assessed a standardized saw palmetto oil (2–3% β-sitosterol) at 400 mg capsules orally or 5 mL of a topical formulation containing 20% of the extract, administered once daily.
Long-Term Dosing
Among 30 patients with benign prostatic hypertrophy treated with saw palmetto at 320 mg once daily for up to 10 years, there was no progression of symptoms and no reported adverse side effects that could be attributed to the herbal supplement.
Extraction Method and Preparation Differences
In a preclinical comparison, an ultrahigh-pressure supercritical CO₂ extract and a hexanic extract of S. repens had nearly identical inhibition curves and comparable IC50 values for 5αR-1 and 5αR-2, suggesting extraction method may not drastically alter 5α-reductase inhibition potency. However, batch-to-batch and brand-to-brand variability in active compound concentrations remains a meaningful concern in the clinical interpretation of results.
7. Safety Profile
General Tolerability
Currently available data suggest that S. repens is well tolerated by most users and is not associated with serious adverse events. The majority of adverse events are mild, infrequent, and reversible. It has been used safely in research studies for up to 3 years. Adverse effects are mild and infrequent; they may include digestive symptoms, dizziness, and headache.
Large clinical trials, including an 18-month NIH-funded study that tested doses up to 960 mg daily (three times the typical dose), found no statistically significant difference in adverse events between saw palmetto and placebo.
Most Commonly Reported Adverse Effects
The most frequently reported adverse events are abdominal pain, diarrhoea, nausea, fatigue, headache, decreased libido, and rhinitis. More serious adverse events such as death and cerebral haemorrhage are reported in isolated case reports and data from spontaneous reporting schemes, but causality is questionable.
Hepatotoxicity
Saw palmetto extracts have many components, but none of them has been shown to be particularly hepatotoxic. The rare cases of liver injury reported with saw palmetto use have had idiosyncratic features. The NIH's LiverTox database rates it as a "possible, rare cause of clinically apparent liver injury," its lowest level of concern. In the handful of reported cases, symptoms appeared within one to two weeks of starting the supplement and resembled a mild viral hepatitis, with liver enzyme levels returning to normal within one to three months after stopping use. No cases have led to liver failure, transplantation, or chronic liver disease. Long-term studies have not found any pattern of liver enzyme elevations during regular use.
Drug Interactions
Saw palmetto has few herb-drug interactions and is not affected by inducers or inhibitors of the cytochrome P450 enzyme system. No drug interactions were identified in the systematic review by Agbabiaka et al.
However, other clinical pharmacology resources note potential interactions with anticoagulant and antiplatelet agents. Saw palmetto can interact with a few categories of medication. The most important ones to know about are blood thinners and antiplatelet drugs: saw palmetto may increase the risk of bleeding when combined with these medications. Sources note that saw palmetto may increase the toxicity of apixaban; this combination should be used with caution and monitored, as it may increase the risk of bleeding. Similar caution has been flagged for other anticoagulants including argatroban, aspirin, and various NSAIDs.
PSA Testing Considerations
Saw palmetto does not appear to affect readings of prostate-specific antigen (PSA) levels, even when taken in higher-than-usual amounts. PSA is a protein produced by the prostate gland. PSA levels have been used to screen for prostate cancer. Saw palmetto may be unsafe for use during pregnancy or while breastfeeding.
Special Populations
Though generally considered safe, saw palmetto is not recommended for children or pregnant or nursing people, and it may interact with blood thinners and oral contraceptives. Evidence for saw palmetto in female hair loss is even more limited than in men, and it must be avoided entirely during pregnancy and breastfeeding.
8. Body Systems and Health Areas of Association
- Urogenital / Prostate: Saw palmetto is most prominently promoted for urinary symptoms associated with an enlarged prostate gland (BPH). Many studies have been conducted on this use, and the current weight of evidence concludes that saw palmetto is probably not helpful for this purpose when used as a standalone therapy.
- Androgenic / Hormonal: In vitro studies have demonstrated biological effects such as inhibition of steroid 5α-reductase and antagonism of α1-adrenergic receptors. These hormonal mechanisms are the basis for its investigation in BPH and hair loss.
- Dermatological / Hair: Oral or topical saw palmetto has been evaluated for androgenetic alopecia, telogen effluvium, seborrheic dermatitis, and reduction of facial sebum. Evidence is preliminary.
- Inflammatory: The berries inhibit cyclooxygenase and 5-lipoxygenase pathways, thereby preventing the biosynthesis of inflammation-producing prostaglandins and leukotrienes.
- Prostatitis: Some data suggest benefits against chronic prostatitis/chronic pelvic pain syndrome, though evidence is mixed and heterogeneous.
References
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