L-citrulline
Amino acid that converts to arginine in the kidney, produces sustained nitric oxide elevation with better tolerability than oral arginine.
Why
L-citrulline is an amino acid found in watermelon and produced in the urea cycle. Oral citrulline bypasses hepatic first-pass extraction (which limits oral arginine's bioavailability) and is converted to arginine in the kidney, producing more sustained plasma arginine elevation than direct arginine supplementation. RCTs report modest reductions in blood pressure, improvements in flow-mediated dilation, and a separate small body of work supports use in mild-to-moderate erectile dysfunction.
How it works
Recycled to L-arginine in the proximal renal tubule, increasing systemic arginine and NO availability without GI side effects of high-dose arginine. Also serves as a urea-cycle intermediate, supporting ammonia clearance.
Expected onset · BP effects over 4–8 weeks; flow-mediated dilation within 2–4 weeks
How to take
Dosage
BP / endothelial function: 3–6 g/day divided. Erectile function: 1.5 g/day divided. Athletic performance trials use up to 8 g pre-exercise.
Timing
Divided 2–3 times daily; pre-exercise for athletic indication
On the label
'L-citrulline' or 'L-citrulline malate' (the malate form is dosed higher to account for the malate portion of the weight).
Ideal for
Adults with mild hypertension or endothelial-dysfunction risk factors; men with mild erectile dysfunction seeking a nutrient approach.
Safety
Evidence
Figueroa 2017 Hypertens Res meta-analysis (8 RCTs): L-citrulline supplementation reduced systolic BP by ~4 mmHg in adults with elevated BP. Cormio 2011 Urology RCT (n=24 mild ED): L-citrulline 1.5 g/day improved erection-hardness score by 50% vs 8% on placebo over one month. More sustained plasma arginine elevation than direct arginine supplementation.
- Figueroa et al., Hypertens Res 2017, effects of L-citrulline supplementation on blood pressure: meta-analysis
- Cormio et al., Urology 2011, oral L-citrulline supplementation improves erection hardness in mild ED (RCT)
- Schwedhelm et al., Br J Clin Pharmacol 2008, pharmacokinetic and pharmacodynamic properties of oral L-citrulline
Where to get it
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