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L-Citrulline
Amino acid that boosts nitric oxide production, improving blood flow, exercise performance, and recovery.
What the evidence says
L-Citrulline helped in about half (2/3) of the studies that measured an effect — promising, but not unanimous.
Most evidence is from high-quality meta-analyses and randomised trials published 1991–2026 with a typical study size of 30 participants.
Based on 163 studies · 15 meta-analyses · 126 RCTs · 884,342 total participants
Confidence
High confidenceWhat the studies found
By outcome
Multiple meta-analyses confirm modest benefits for muscle soreness, perceived exertion and blood pressure in older adults, but several show no effect on endurance, body composition or oxidative stress, keeping evidence moderate.
22 trials ongoing or recruiting · 97 completed on ClinicalTrials.gov
10 of the completed trials have posted results
Registered trials show research momentum for L-Citrulline, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Oct 2026
L-Citrulline is an amino acid that converts to L-arginine in the kidneys, leading to increased nitric oxide production. This vasodilation effect improves blood flow, exercise performance, and may reduce muscle soreness. It's more effective than supplementing with arginine directly due to better absorption.
Increases blood vessel dilation for better blood flow
Helps remove exercise-induced ammonia buildup
May support cellular energy during exercise
How L-Citrulline works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Insufficient data; avoid supplementation
Consult doctor due to effects on blood pressure
Combined effect may cause dangerous drop in blood pressure A grade for this interaction is held for clinical review and has not been validated, so no severity is given. The precaution still applies: ask a pharmacist about the exact supplement and medicine. Do not stop or change prescribed medicines based on this notice.
May enhance blood pressure lowering effects
May have additive blood pressure lowering effects
Tip: Take with food or reduce dose
Tip: Reduce dose
L-Citrulline has an evidence score of 6/10 — moderate evidence based on 163 indexed studies, including 7 meta-analyses. Amino acid that boosts nitric oxide production, improving blood flow, exercise performance, and recovery. Representative study: PMID 37111214.
The commonly studied dose of L-Citrulline is 3-6g (or 6-8g citrulline malate). Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take L-Citrulline is between meals. It can be taken on an empty stomach. L-citrulline is a non-proteinogenic amino acid that bypasses hepatic first-pass metabolism and is converted to L-arginine in the kidneys, making it the most efficient oral route to raise systemic arginine and nitric oxide levels.
L-Citrulline has a safety rating of "moderate". That is a category, not a measure of individual risk, and there are precautions worth knowing. Reported side effects are uncommon and include stomach discomfort, diarrhea. Use caution if any of these apply to you: Those taking nitrates or PDE5 inhibitors (Viagra, Cialis); Low blood pressure.
Citrulline Malate
Probably helpsCombines citrulline for nitric oxide production with malic acid for ATP synthesis — reduces fatigue and enhances exercise endurance.
Creatine
Likely helpsIncreases phosphocreatine stores for faster ATP regeneration, boosting strength, power output, and cognitive function under stress.
Whey Protein
Likely helpsComplete protein with high leucine content that maximizes muscle protein synthesis.
Arginine
Likely helpsPrimary substrate for nitric oxide production — dilates blood vessels to improve circulation, exercise performance, and cardiovascular health.
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Reviewed by Dr. Baher Al Hakim · Last reviewed May 2026 · evidence from 163 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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