Big effect
A 36% larger improvement in blood vessel dilation with 3 g/day L-citrulline — but only in people with high-normal blood pressure at baseline.
This moderate-sized, rigorous trial adds to a consistent body of evidence (5 out of 5 studies beneficial) that L-citrulline can improve vascular function, but the effect appears to depend on starting blood pressure — meaning healthy people with low-normal BP might not see the same benefit.
In a 12-week, double-blind trial with 66 healthy adults, those with high-normal blood pressure who took 3,000 mg/day of L-citrulline had significantly better flow-mediated dilation — a measure of how well blood vessels relax — than the placebo group. The effect was not seen in participants with lower blood pressure, suggesting the supplement's vascular benefits are specific to people whose blood pressure is already on the higher side of normal.
Where this fits in the evidence
Pillser has synthesized 5 studies on L-Citrulline for Improved Flow-Mediated Dilation — overall evidence strength: Moderate.
Across 5 studies, all reported beneficial effects of L-citrulline on flow-mediated dilation (FMD), with effect sizes ranging from small to large (most commonly moderate). The median study duration was 28 days, and the most studied dose range was 6–10 g/day. Evidence primarily comes from clinical populations with hypertension, type 2 diabetes, or heart failure, suggesting L-citrulline may improve endothelial function in these groups.
The study
- Randomized Controlled Trial (RCT)
- n = 66
- 2026-06
- Nutrition research (New York, N.Y.)
This is a plain-language summary of a research finding, not medical advice. Pillser surfaces research signals to help you decide what's worth investigating — always consult a qualified professional before changing what you take.