How Long Does Saw Palmetto Take to Work for the Prostate? What Each Trial Saw, Week by Week
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If saw palmetto helps at all, the trials suggest you would notice within about 8 to 12 weeks, and longer use did not make it beat placebo.4,1 Trials lasting one year and 72 weeks found no difference from placebo.2,3 Score your symptoms before you start and again at week 12.
Supplement sellers often answer this question with "give it a few months." That sounds reasonable until you line up the trials and see what happened in the placebo group over the same months. This page does exactly that, with every study linked.
Key takeaways
- In a 2020 Japanese trial of 40 men taking 320 mg a day, saw palmetto beat placebo at week 8 (symptom score down 4.1 vs 1.6 points), but by week 12 the gap was no longer significant (4.3 vs 3.3).4
- The 2023 Cochrane review of 27 studies and 4,656 men found little to no difference from placebo at 3 to 6 months (0.90 points on a 35-point scale) and at 12 to 17 months (0.07 points).1
- The STEP trial (225 men, 1 year, 160 mg twice a day) found a difference of 0.04 points between saw palmetto and placebo.2
- In the CAMUS trial (369 men, 72 weeks, dose raised to 960 mg a day), the placebo group improved 2.99 points and the saw palmetto group 2.20.3
- Men who rated themselves "slightly improved" had dropped about 3.1 points on the AUA symptom index, which makes 3 points a practical yardstick for your own test.5
Why "how long" is the right question to ask
Saw palmetto is the most studied herb for urinary symptoms linked to an enlarged prostate (BPH), the condition behind most of the enlarged prostate symptoms men notice after 50. Its trials are unusual for a supplement: several were long, large and independently run. That means the timeline question has a real answer, and it is not the one on most bottles.
Two numbers will keep coming up, so here is what they mean. The IPSS (International Prostate Symptom Score) and the AUA symptom index use the same seven questions, scored 0 to 35, where higher is worse. A "change of 4 points" means the score fell by 4 on that scale. You can take the same test yourself with our IPSS score calculator.
The saw palmetto timeline, trial by trial
| Study | Men and dose | How long | What it found | Evidence level |
|---|---|---|---|---|
| Ishii et al., Japan, 20204 | 44 men aged 40 to 69 (40 analyzed), 320 mg a day | 12 weeks | Week 4: no difference. Week 8: score down 4.1 vs 1.6 on placebo (significant). Week 12: down 4.3 vs 3.3 (not significant). | Small, funded by two supplement makers |
| Cochrane review, 2023 (short term)1 | 9 low-risk-of-bias studies, 1,681 men | 3 to 6 months | 0.90 points better than placebo on a 35-point scale: "little to no difference" | High certainty |
| STEP trial, US, 20062 | 225 men over 49 with moderate to severe symptoms, 160 mg twice a day | 1 year | 0.04 points difference in symptom score; no difference in flow, prostate size or residual urine | Large, independent, double-blind |
| Cochrane review, 2023 (long term)1 | 3 studies, 898 men | 12 to 17 months | 0.07 points difference: "little to no difference" | High certainty |
| CAMUS trial, North America, 20113 | 369 men aged 45 and older, 320 mg a day, raised to 640 mg at week 24 and 960 mg at week 48 | 72 weeks | Symptom score down 2.20 on saw palmetto and 2.99 on placebo; no advantage on any secondary outcome | Large, independent, double-blind |
Read the table from top to bottom and a pattern appears. The only signal in favor of saw palmetto shows up early, in a small industry-funded trial, at a single time point. Every longer and larger study found the herb and the placebo pill ending up in about the same place.
What happens in the first 4 to 8 weeks?
The Japanese study is the one most product pages quote, so it deserves a close read. Researchers gave 320 mg of saw palmetto fruit extract or a placebo once a day for 12 weeks to men aged 40 to 69 who woke at least twice a night to urinate. The study was sponsored by Yawata Corporation and Nihon Pharmaceutical.4
- Week 4: both groups had dropped a little over 1 point (1.3 on saw palmetto, 1.4 on placebo).
- Week 8: saw palmetto 4.1 points down, placebo 1.6. This was the only time point with a statistically significant difference in the total score.
- Week 12: saw palmetto 4.3 points down, placebo 3.3. The difference was no longer significant.4
So the honest reading is not "saw palmetto starts working at 8 weeks." It is "in one small trial, men on saw palmetto improved faster, and the placebo group caught up by week 12." The quality-of-life score did not differ between the groups at any visit.4
What happens at 3 to 6 months?
This is the window most people mean when they ask how long saw palmetto takes. The 2023 Cochrane review, the most complete summary available, pooled the studies at low risk of bias and found saw palmetto improved the symptom score by 0.90 points more than placebo at 3 to 6 months. The authors rate that as "little to no difference," with high-certainty evidence, and quality of life did not meaningfully change either.1
For scale: in a large Veterans Affairs trial, men who said they felt "slightly improved" had dropped about 3.1 points.5 An extra 0.9 points is below what most men would notice.
What happens after a year or more?
Two independently run US trials answered the "maybe it just needs more time" argument directly:
- STEP (2006) gave 160 mg twice a day for a full year. The difference in symptom score versus placebo was 0.04 points, and there was no difference in flow rate, prostate size, leftover urine, quality of life or PSA.2
- CAMUS (2011) went further: it ran 72 weeks and raised the dose twice, to 640 mg at week 24 and 960 mg at week 48. The placebo group still did slightly better (2.99 vs 2.20 points), and saw palmetto was no better on any secondary outcome.3
The previous version of the American Urological Association guideline (2021, amended 2023) cites both trials and says they found "no benefit over placebo in terms of symptoms, bother, QoL, flowrate recordings, serum PSA, or any other measurable parameter."6 The NCCIH concludes that saw palmetto "is probably not helpful" for these symptoms.7
Why do so many men feel better on saw palmetto?
Because many men feel better on placebo too, and the trial numbers show how much. In CAMUS the placebo group's score fell by almost 3 points over 72 weeks.3 In the Japanese trial it fell 3.3 points in 12 weeks.4 That is about the size of change men describe as "slightly improved."5
The trials do not explain why the placebo groups improved, and they did not need to: the point of a placebo group is to measure how much men improve without the active ingredient. None of this means your improvement is imaginary. It means that feeling better after three months on a supplement does not, by itself, show the supplement caused it. Only a comparison with placebo can, and that is what the large trials did.
The information most timeline pages leave out: in the longest trials, the placebo group improved by 2 to 3 points too. Any "results in 30 days" claim has to beat that, and none of the large independent trials found that saw palmetto did.
A 12-week test you can run yourself
If you decide to try saw palmetto anyway, a fixed test keeps you from taking it for years on hope. This is a practical plan built from the trial timelines, not a medical protocol:
- Day 0: take the IPSS and write down the total and the date. If you can, keep a 3-day record of how often you urinate, especially at night.
- Change one thing only. If you also cut evening drinks or caffeine, you will not know which change helped.
- Use a dose that matches the studies. The trials above started at 320 mg a day of extract (once, or 160 mg twice).2,3,4 Our saw palmetto dosage guide explains how to check whether a label actually delivers that.
- Week 12: take the IPSS again under the same conditions.
- Read the result: a drop of 3 points or more is roughly what men notice as "slightly improved."5 Less than that, after 12 weeks, matches what the large trials saw: little to no effect. Taking it longer did not change that result in STEP or CAMUS.2,3
This also lines up with medical follow-up. The AUA's 2026 guideline states that "Patients with LUTS/BPH should be re-evaluated within six months of treatment initiation, to assess response and treatment-related adverse effects."8 The previous version (2021, amended 2023) set the first check at 4 to 12 weeks after starting treatment, with the IPSS repeated.6 Those statements are about prescribed treatment, but the logic works for a supplement too: decide in advance when you will check, and check.
What if saw palmetto is not working?
If your score has not dropped by about 3 points after 12 weeks, the evidence gives little reason to expect a change at 6 or 12 months. A few things are worth doing instead of simply waiting:
- Check that you were actually taking a studied dose. Many blends list saw palmetto as berry powder or inside a proprietary blend, which is not the same as 320 mg of extract. See how to read a prostate supplement label.
- Look at the habits first. The AUA's 2026 guideline says: "Behavioral and lifestyle interventions should be explored before or alongside pharmacologic treatment."8
- Compare other options honestly. Our page on saw palmetto vs pygeum lays out what the trials of each herb found.
- See a doctor if anything gets worse. The European Medicines Agency monograph on saw palmetto says to consult a doctor or pharmacist if complaints worsen, or if fever, spasms, blood in the urine, painful urination or urinary retention occur.9
If you take prescription medicine, including tamsulosin, finasteride or a blood thinner, read saw palmetto drug interactions before adding it. Do not stop or change a prescribed medicine without your doctor.
What is the best time of day to take saw palmetto?
No trial compared morning with evening, so there is no evidence-based best hour. The trials simply used different schedules: STEP split the dose, 160 mg twice a day, and the Japanese trial used one capsule a day.2,4 The European Medicines Agency monograph lists both options, 320 mg once daily or 160 mg twice daily.9
Food matters more than the clock. The same monograph lists nausea, vomiting, diarrhea and abdominal pain as uncommon side effects, "especially when taken on an empty stomach."9 Taking it with a meal you never skip is the simplest way to remember it and to avoid stomach upset.
Is it safe to keep taking saw palmetto long term?
For most men it appears to be. The NCCIH says saw palmetto is well tolerated, has been used safely in research studies for up to 3 years, and that side effects are mild and infrequent, such as digestive symptoms, dizziness and headache.7 The Cochrane review found it probably makes little to no difference in adverse events compared with placebo.1 CAMUS identified no clearly attributable adverse effects even at 960 mg a day.3
Safety is not the same as value, though. A supplement that is safe but does not help still costs money every month and can delay a checkup for symptoms that deserve one. That is why the 12-week checkpoint matters. It also cannot change the size of the prostate; if that is your question, see can an enlarged prostate shrink.
Where a supplement fits
A supplement comes after the checkup, not instead of it: once a urinalysis, an exam and a PSA have ruled out other causes. Even then, set a deadline. If you are comparing products, the question to ask of any label is whether each ingredient is listed with its amount, and whether those amounts match the doses in the trials above.
A fair test needs the dose the trials used: 320 mg of saw palmetto extract a day. A single-ingredient extract that prints that number on the label is the cleanest way to run the 12-week check above.
ProtoFlow is a different kind of product: a 14-ingredient formula with 84.5 mg of saw palmetto per day, about a quarter of the trial dose, plus herbs sold for male vitality such as epimedium, damiana and tribulus. Its maker says it "supports the normal functions of the bladder, prostate and reproductive system".
Our review lays out the full label, the dose math and the refund terms, so you can decide whether it fits what you want to test.
A practical plan for this week
- Today: take the IPSS and save the total with the date.
- This week: check your bottle for the saw palmetto amount and form (extract or berry powder).
- Put a reminder in your calendar 12 weeks from today to retake the score.
- Bring both scores and your medicine list to your next visit.
- Anytime: if you cannot urinate, have fever with urinary symptoms or see blood in your urine, get care now.
Frequently asked questions
How long does saw palmetto take to work for the prostate?
In the trials that found any early difference, it appeared at about 8 weeks. In a 2020 Japanese study, men on 320 mg a day improved more than placebo at week 8, but the placebo group caught up by week 12. Larger trials lasting one year and 72 weeks found no difference from placebo, so waiting longer is not supported by the evidence.
How do I know if saw palmetto is working?
Score your symptoms with the IPSS before you start and again after 12 weeks. In a large Veterans Affairs trial, men who felt slightly improved had dropped about 3.1 points on the American Urological Association symptom index. A drop smaller than about 3 points after 12 weeks suggests little or no effect.
Should I keep taking saw palmetto if it is not working after 3 months?
The evidence gives little reason to expect a later effect. The STEP trial ran for one year and the CAMUS trial for 72 weeks with doses up to 960 mg a day, and neither found a benefit over placebo. Talk with your doctor about other options, and do not stop or change a prescribed medicine without your doctor.
Does saw palmetto work better if you take it longer?
Not in the trials. The 2023 Cochrane review found little to no difference from placebo at 3 to 6 months and again at 12 to 17 months. In CAMUS, men took saw palmetto for 72 weeks while the dose was raised twice, and the placebo group improved slightly more.
What is the best time of day to take saw palmetto?
No trial compared morning and evening. Trials used either 160 mg twice a day or one 320 mg capsule a day. The European Medicines Agency monograph notes that stomach side effects are more likely when it is taken on an empty stomach, so taking it with a meal is a sensible default.
Why do some men say saw palmetto works for them?
Placebo groups improve too. In the CAMUS trial, men taking a placebo improved by almost 3 points over 72 weeks, and in a 12-week Japanese trial by 3.3 points. Feeling better on a supplement is real, but it does not show the supplement caused the change.
Is it safe to take saw palmetto for years?
It appears to be safe for most men. The National Center for Complementary and Integrative Health says it is well tolerated and has been used safely in research for up to 3 years, with mild and infrequent side effects such as digestive symptoms, dizziness and headache. Ask your doctor first if you take blood thinners or other medicines.
Sources
- Franco JV, Trivisonno L, Sgarbossa NJ, et al. Serenoa repens for the treatment of lower urinary tract symptoms due to benign prostatic enlargement. Cochrane Database of Systematic Reviews. 2023;6(6):CD001423. https://pubmed.ncbi.nlm.nih.gov/37345871/
- Bent S, Kane C, Shinohara K, et al. Saw palmetto for benign prostatic hyperplasia. New England Journal of Medicine. 2006;354(6):557-566. https://pubmed.ncbi.nlm.nih.gov/16467543/
- Barry MJ, Meleth S, Lee JY, et al. Effect of increasing doses of saw palmetto extract on lower urinary tract symptoms: a randomized trial. JAMA. 2011;306(12):1344-1351. https://pubmed.ncbi.nlm.nih.gov/21954478/
- Ishii I, Wada T, Takara T. Effects of saw palmetto fruit extract intake on improving urination issues in Japanese men: a randomized, double-blind, parallel-group, placebo-controlled study. Food Science & Nutrition. 2020;8(8):4017-4026. Open access. https://pmc.ncbi.nlm.nih.gov/articles/PMC7455929/
- Barry MJ, Williford WO, Chang Y, et al. Benign prostatic hyperplasia specific health status measures in clinical research: how much change in the American Urological Association symptom index and the benign prostatic hyperplasia impact index is perceptible to patients? Journal of Urology. 1995;154(5):1770-1774. https://pubmed.ncbi.nlm.nih.gov/7563343/
- American Urological Association. Management of Lower Urinary Tract Symptoms Attributed to Benign Prostatic Hyperplasia: AUA Guideline (2021, amended 2023), unabridged. Previous version, replaced on May 7, 2026. https://www.auanet.org/documents/Guidelines/PDF/2023%20Guidelines/BPH%20Unabridged%2002-20-24%20Final.pdf
- National Center for Complementary and Integrative Health (NIH). Saw Palmetto: Usefulness and Safety. https://www.nccih.nih.gov/health/saw-palmetto
- American Urological Association. Management of Lower Urinary Tract Symptoms Attributed to Benign Prostatic Hyperplasia: AUA Guideline (2026). Released May 7, 2026; replaces the 2021 guideline amended in 2023. https://www.auanet.org/2026BPHGuideline
- European Medicines Agency, Committee on Herbal Medicinal Products. European Union herbal monograph on Serenoa repens (W. Bartram) Small, fructus. EMA/HMPC/280079/2013. https://www.ema.europa.eu/en/documents/herbal-monograph/final-european-union-herbal-monograph-serenoa-repens-w-bartram-small-fructus_en.pdf
About the author
Alice Hess is a health researcher and wellness writer at ProstateClarity. She is not a doctor, a nurse, a nutritionist or any kind of licensed clinician, and nothing here is medical advice. She started this work because of her father: at 76 he was getting up several times a night, and the research she did for him helped him get back to sleeping through the night. One man's story is not evidence, which is why every guide here is built on published research. She reads labels, primary research and regulatory limits, and publishes the numbers manufacturers leave out. More about her work and how these articles are researched.
Found an error? Write to contact@prostateclarity.com with the sentence and the source that contradicts it. Corrections are made in the article with the date noted.