L-Citrulline
Increases nitric oxide production for better pumps, endurance, and blood pressure.
What is L-Citrulline?
L-citrulline is an amino acid found naturally in watermelon. Unlike L-arginine (which it converts to in the kidneys), citrulline bypasses first-pass metabolism in the gut and liver, making it far more effective at raising arginine and nitric oxide levels. Nitric oxide is a vasodilator, relaxing blood vessels and improving blood flow to muscles.
What does the evidence say?
A 2010 study by Pérez-Guisado and Jakeman found citrulline malate at 8g reduced muscle soreness by 40% and improved repetition performance in upper-body training. A 2016 meta-analysis by Sureda and Pons confirmed improvements in exercise performance and reduced perceived effort. Separate research shows potential benefits for erectile function and blood pressure via the same nitric oxide pathway.
Good evidence from several studies, but with some limitations in size, duration, or methodology.
Dosage guide
| Effective dose | 6–8g of L-citrulline or 8–10g of citrulline malate per day |
| Maximum dose | No established upper limit, but studies use up to 10g without reported issues |
| Timing | 30 to 60 minutes before training for acute performance effects. |
Best form to buy
L-citrulline (pure) or citrulline malate (2:1 ratio). The pure form requires a lower dose to achieve the same citrulline intake. Malate may add slight anti-fatigue benefits from the malic acid component.
Who benefits most
Men doing high-volume training or any cardiovascular exercise. Also relevant for men with mildly elevated blood pressure or concerns about erectile function.
Side effects and safety
Generally very well tolerated. High doses can occasionally cause mild GI discomfort. Theoretically may interact with blood pressure medication.
“This is the ingredient in most pre-workout powders that actually does something. Far more effective than L-arginine for the same purpose. The blood pressure and erectile function research is genuinely interesting and often overlooked.”