Guide
How long does saw palmetto take to work?
There's no single answer, because it depends what you mean by "work." For urinary symptoms, the largest and longest trials — up to 72 weeks — found no benefit over placebo at any point measured. For hair growth, one placebo-controlled trial measured change at 90 and 180 days and found the largest gains by the later mark, so the honest answer is that timelines vary by outcome and the biggest body of trial data found no effect to time at all.
There's no single answer, because it depends what "work" means. For urinary symptoms — the outcome most saw palmetto trials measured — the largest, longest trials tracked people for up to 72 weeks and found no benefit over placebo at any point along the way, at any dose tested. For hair growth, a smaller but placebo-controlled trial measured change at 90 and 180 days and found a larger gap over placebo at the later mark. Different question, different timeline, different result.
Urinary symptoms: no "kicks in" point, because no benefit was found
A 2006 trial followed 225 men for a full year at the standard dose (320 mg/day) and found no significant difference from placebo in symptom scores at any measured point during that year. The CAMUS trial went further, following 369 men for 72 weeks while escalating the dose from 320 mg/day up to 960 mg/day, and still found no difference from placebo on the main symptom score or on ten secondary measures, at any dose or duration tested. A 2012 Cochrane review pooling 32 trials, with individual trial lengths from 4 to 72 weeks, reached the same conclusion at every timeframe studied. For this outcome, "how long does it take to work" doesn't really have an answer, because the trials found it didn't.
Hair growth: measured at 90 and 180 days
A different, more recent placebo-controlled trial tested a specific saw palmetto extract for self-perceived hair thinning in 60 adults (40 on active treatment, 20 on placebo, half of them women), with assessments at baseline, 90 days, and 180 days. The active group showed significantly greater hair counts than placebo at the 90-day mark, and the advantage over placebo was roughly 40% larger by 180 days than it had been at 90 — meaning what improvement there was kept building rather than plateauing early. That's one trial of one specific extract at 160 mg/day, not the standard 320 mg/day liposterolic extract used in the urinary-symptom trials above, so it doesn't tell you how long a different product or dose would take.
What that means in practice
No trial measured saw palmetto working in days. Every study — whether it found an effect or not — measured outcomes in weeks to months, with the longest running 72 weeks. If you're taking it for urinary symptoms, the honest answer from the largest trials is that more time didn't produce a benefit at any point they checked. If you're taking it for hair, the one placebo-controlled trial that measured this took 90 to 180 days to show its full effect, and that data comes from one specific extract, not saw palmetto as a category.
Questions people ask
Does saw palmetto work?
It depends on the outcome. For urinary symptoms, the largest, best-designed trials found it performed no better than placebo, even at triple the standard dose over 72 weeks. For hair growth, one placebo-controlled trial of a specific extract found a benefit building over 90 to 180 days. Full detail on both is in saw palmetto benefits: what the research does and doesn't show.
How does saw palmetto work?
The proposed mechanism is blocking 5-alpha-reductase, the enzyme that converts testosterone into DHT. A laboratory study on cells in a dish supports that mechanism exists, but the largest human trials on urinary symptoms didn't find the clinical benefit that mechanism would predict.
How long does saw palmetto stay in your system?
No trial we found measured this directly — how long its compounds remain detectable, or how long any effect lasts, after stopping.
How long can you take saw palmetto?
The longest controlled trial ran 72 weeks (about a year and a half) without an unusual safety signal at that length. No trial has followed people taking it longer than that, so there's no long-term data beyond a year and a half either way.
Related reading: how much saw palmetto should you take a day, saw palmetto benefits: what the research does and doesn't show, and when is the best time to take saw palmetto.
Sources
- Saw palmetto for benign prostatic hyperplasia A one-year randomized trial in 225 men found the standard dose of saw palmetto extract (320 mg/day) performed no better than placebo on urinary symptom scores or urine flow.
- Effect of increasing doses of saw palmetto extract on lower urinary tract symptoms: a randomized trial A 72-week randomized trial that escalated saw palmetto up to triple the standard dose (960 mg/day) in 369 men found it did not reduce urinary symptoms more than placebo at any dose tested.
- Serenoa repens for benign prostatic hyperplasia A Cochrane review pooling 32 randomized trials in 5,666 men found saw palmetto, even at double and triple the standard dose, was no better than placebo for urinary symptom scores, urine flow, or prostate size.
- The Safety and Efficacy of a Proprietary Bioactive Fatty Acids Extract From Saw Palmetto (Serenoa repens) for Promoting Hair Growth and Reducing Hair Loss in Adults With Self-Perceived Thinning Hair: 90-Day Results A placebo-controlled trial of a specific 160 mg/day saw palmetto extract found significantly greater hair counts than placebo at 90 days in 60 adults, half of them women.
- The Safety and Efficacy of a Novel Saw Palmetto (Serenoa repens) Extract for Promoting Hair Growth in Adults With Self-Perceived Thinning Hair: 180-Day Results The 180-day results of the same trial found the treated group's advantage over placebo grew larger between Day 90 and Day 180, in both men and menopausal women.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.