L-Citrulline
L-Citrulline
Amino acid that boosts nitric oxide production, improving blood flow, exercise performance, and recovery.
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.
Mechanisms of Action
Nitric Oxide Production
Increases blood vessel dilation for better blood flow
Ammonia Clearance
Helps remove exercise-induced ammonia buildup
ATP Production
May support cellular energy during exercise
Recommended Dose
3-6g (or 6-8g citrulline malate)
Optimal Timing
- 30-60 minutes before exercise
- Or split doses throughout day
Can be taken without food
Best Form
L-Citrulline powder (pure form)
Alternatives: Citrulline Malate (2:1 ratio), Capsules
Pure L-citrulline is more concentrated. Citrulline malate includes malic acid which may have additional benefits for energy production.
Duration
Minimum: 1 weeks
Optimal: 2 weeks
Cycling: Not required
Note: Can be taken on empty stomach. For chronic benefits, daily dosing is more important than timing. Citrulline malate is ~56% citrulline by weight.
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Improved Endurance
Better performance in prolonged exercise
Reduced Muscle Soreness
Less DOMS after intense training
Enhanced Muscle Pump
Better blood flow during resistance training
GI Discomfort
Some experience stomach issues at high doses
Insufficient data; avoid supplementation
Consult doctor due to effects on blood pressure
Who Should NOT Take This
- Those taking nitrates or PDE5 inhibitors (Viagra, Cialis)
- Low blood pressure
Drug Interactions
Combined effect may cause dangerous drop in blood pressure
May enhance blood pressure lowering effects
May have additive blood pressure lowering effects
Possible Side Effects
Tip: Take with food or reduce dose
Tip: Reduce dose
Warnings
- Avoid combining with medications that lower blood pressure
- Start with lower doses to assess tolerance
Beetroot/Nitrates
enhancesBoth boost nitric oxide through different pathways
Maximized nitric oxide production and blood flow
Beta-Alanine
complementaryDifferent mechanisms for endurance
Citrulline for blood flow, beta-alanine for acid buffering
Agmatine
complementaryBoth affect nitric oxide pathways
Enhanced vasodilation and muscle pumps
Arginine
complementaryCitrulline converts to arginine in the kidneys
Sustained nitric oxide production; citrulline has better bioavailability
Top studies from 40+ peer-reviewed papers
Porto AA et al. • Nutrients (2023)
“In conclusion, our systematic review and meta-analysis found that L-Citrulline and L-Arginine did not influence inflammatory biomarkers and oxidative stress after exercise.”
Key Findings:
- We observed no difference between pre- vs. post-exercise for oxidative stress (subtotal = -0.21 [CI: -0.56, 0.14], p = 0.24, and heterogeneity = 0%.
- In the sub-group "L-Arginine" we found a subtotal = -0.29 [-0.71, 0.12], p = 0.16, and heterogeneity = 0%.
- No differences were observed between groups (p = 0.47), and I² = 0%) or in antioxidant activity (subtotal = -0.28 [-1.65, 1.08], p = 0.68, and heterogeneity = 0%).
- In the "L-Arginine" sub-group, we found a subtotal = -3.90 [-14.18, 6.38], p = 0.46, and heterogeneity was not applicable.
Makama M et al. • BJOG : an international journal of obstetrics and gynaecology (2025)
“L-arginine may be promising for pre-eclampsia prevention and treatment, but findings should be interpreted cautiously.”
Key Findings:
- In prevention trials, L-arginine was associated with a reduced risk of pre-eclampsia (relative risk [RR] 0.52; 95% confidence interval [CI], 0.35, 0.78; low-certainty evidence, four trials) and severe pre-eclampsia (RR 0.23; 95% CI, 0.09, 0.55; low-certainty evidence, three trials).
- In treatment trials, L-arginine may reduce mean systolic blood pressure (MD -5.64 mmHg; 95% CI, -10.66, -0.62; very low-certainty evidence, three trials) and fetal growth restriction (RR 0.46; 95% CI, 0.26, 0.81; low-certainty evidence, two trials).
- L-arginine may be promising for pre-eclampsia prevention and treatment, but findings should be interpreted cautiously.
- More trials are needed to determine the optimal dose and time to commence supplementation and support clinical decision-making.
Ashtary-Larky D et al. • Nutrients (2025)
“CIT supplementation appears to have no overall effect on body composition.”
Key Findings:
- Overall, CIT supplementation had no substantial effects on body mass index (BMI), body weight, fat mass (FM), waist circumference (WC), body fat percentage (BFP), and fat-free mass (FFM).
- Interventions lasting 3 to 8 weeks were associated with a significant increase in FFM.
- CIT supplementation appears to have no overall effect on body composition.
- However, exploratory findings indicated potential benefits at higher doses or shorter durations.
Winer N et al. • The American journal of clinical nutrition (2025)
“The current trial found no benefit of oral L-citrulline supplementation to females with PE regarding either the duration of pregnancy, fetal growth, or maternal and neonatal outcomes.”
Key Findings:
- The duration of pregnancy between inclusion and delivery was unaltered (hazard ratio: 0.90; 95% confidence interval: 0.62, 1.31).
- Liver enzymes were higher on the day of delivery in the treated, compared to the placebo group (65.1 compared with 33.2 UI and 70.4 compared with 33.7 UI for alanine aminotransferase and aspartate aminotransferase, respectively, (estimate: 5.92; 95% confidence interval: 1.09, 10.74).
- Systolic blood pressure (BP) was higher at delivery in the citrulline group compared with the control group (P = 0.015), whereas the diastolic BP showed no difference.
d'Unienville NMA et al. • Journal of the International Society of Sports Nutrition (2021)
“Foods rich in polyphenols and nitrate provide trivial benefits for endurance exercise performance, although these effects may be food dependent.”
Key Findings:
- No effect on exercise performance following consumption of foods rich in L-citrulline was identified (SMD=-0.03, p=0.24).
- Foods rich in polyphenols and nitrate provide trivial benefits for endurance exercise performance, although these effects may be food dependent.
- Highly trained endurance athletes do not appear to benefit from consuming nitrate-rich foods but may benefit from polyphenol consumption.
- Further research into food sources, dosage and supplementation duration to optimise the ergogenic response to polyphenol consumption is warranted.
Study Type Distribution
Goals This Supplement Supports
Related Goals
This information is for educational purposes only and is not intended as medical advice. Always consult a qualified healthcare provider before starting any supplement.