L-Citrulline
L-Citrulline
TL;DR
L-citrulline raises plasma arginine and nitric oxide more effectively than arginine itself because it escapes intestinal and hepatic breakdown. Six to eight grams an hour before training improves repetitions to failure and reduces soreness; 3-6 g/day lowers blood pressure modestly.
Ideal For
- Lifters doing high-volume, multi-set resistance work
- Endurance athletes seeking better blood flow and ammonia clearance
- Adults with elevated but not severe blood pressure
- Older adults with reduced muscle protein synthesis
- Men with mild erectile dysfunction
Avoid If
- You take PDE5 inhibitors such as sildenafil — additive hypotension
- You take nitrates for angina
- You have hypotension or are prone to dizziness on standing
- You have severe renal impairment, since conversion occurs in the kidney
Frequently Asked Questions
Overview
L-citrulline is a non-protein amino acid named after watermelon, where it was first isolated. Its value comes from a metabolic quirk: oral arginine is largely destroyed by intestinal and hepatic arginase before it reaches the circulation, whereas citrulline passes through untouched and is converted to arginine in the kidneys. Gram for gram, citrulline raises plasma arginine more than arginine does.
Downstream, that arginine feeds endothelial nitric oxide synthase. More nitric oxide means vasodilation, lower peripheral resistance and improved blood flow to working muscle. Meta-analyses of citrulline supplementation show reductions of roughly 4 mmHg systolic and 2 mmHg diastolic, with larger effects in people who start hypertensive. Citrulline also participates in the urea cycle, accelerating ammonia clearance, which is the likely explanation for reduced fatigue during high-volume sets.
The performance literature is reasonably consistent for citrulline malate at 6-8 g taken 60 minutes pre-exercise: more repetitions to failure in multi-set resistance protocols and lower muscle soreness at 24 and 48 hours. Note that citrulline malate is roughly 1.75:1 citrulline to malate, so an 8 g dose delivers about 4.6 g of citrulline — read labels carefully. Pure L-citrulline at 3-6 g is the cleaner choice for cardiovascular use.
How It Works
- Bypasses intestinal and hepatic arginase, unlike oral L-arginine
- Converted to L-arginine in the renal proximal tubule, raising systemic arginine
- Increases endothelial nitric oxide synthase substrate availability and NO production
- Promotes vasodilation, lowering systolic and diastolic blood pressure
- Feeds the urea cycle, accelerating ammonia clearance during intense exercise
- Enhances muscle protein synthesis signalling via mTORC1 in older adults
- Improves blood flow and oxygen delivery to working skeletal muscle
Quick Facts
- Converts to arginine efficiently
- Boosts nitric oxide production
- Enhances muscle pump
- Improves exercise performance
- Reduces muscle soreness
Benefits & Outcomes
Endothelial Function
One of the better-evidenced supplements for vascular function, with a clear dose-response.
Arterial Flexibility
Citrulline raises nitric oxide availability and modestly lowers arterial stiffness.
Capillary Density
Citrulline improves tissue perfusion and exercise performance but has not been shown to increase capillary number.
VO2 Max Improvement
Citrulline improves blood flow measures with inconsistent aerobic capacity effects.
Sexual Stamina
Citrulline supports blood flow and general exercise endurance, with weak direct sexual stamina data.
Sprint Performance
Citrulline is better supported for volume work than for sprint speed.
Venous Return
Citrulline improves arterial vasodilation, which is not the same as venous return.
Pump Enhancement
Citrulline is the best-supported pump supplement, and it also modestly improves training volume.
Nitric Oxide Production
The most effective oral route to higher plasma arginine and NO.
Oxygen Utilization Improvement
Citrulline improves blood flow and reduces perceived exertion, but its effect on true oxygen utilisation is modest.
Lactic Acid Clearance
Citrulline improves blood flow and reduces soreness but affects lactate handling only indirectly.
Sexual Arousal
Citrulline improves nitric oxide availability with modest clinical results for mild erectile difficulty.
Erectile Function
Moderate evidence for mild ED; not a replacement for PDE5 inhibitors in significant dysfunction.
Enhanced Athletic Performance
Popular as a pump and performance aid; measured effects are small and inconsistent.
Blood Pressure Regulation
Citrulline modestly lowers blood pressure in some populations, with effects in the low single digits.
Endurance Enhancement
Citrulline malate may extend time to exhaustion and reduce soreness, but trials are heterogeneous.
Supporting Research11 studies
Efficacy of L-citrulline oral supplementation in mild erectile dysfunction
Cormio L, De Siati M, Lorusso F +4 more
Erection hardness improved from mild dysfunction to normal in 50% of citrulline patients versus 8.3% on placebo
Acute Effects of Citrulline Supplementation on High-Intensity Strength and Power Performance: A Systematic Review and Meta-Analysis
Trexler ET, Persky AM, Ryan ED +3 more
Acute citrulline supplementation produced a small but statistically significant improvement in high-intensity strength and power performance versus placebo.
L-citrulline supplementation and nitric oxide metabolites: a systematic review and meta-analysis of randomized trials
Barkhidarian B, Khorshidi M, Shab-Bidar S +1 more
L-citrulline raised plasma arginine and nitric oxide metabolites and modestly reduced blood pressure
Citrulline malate supplementation and exercise performance: a systematic review and meta-analysis
Trexler ET, Persky AM, Ryan ED +3 more
Citrulline produced a small but significant improvement in strength and power performance
Effect of food sources of nitrate, polyphenols, L-arginine and L-citrulline on endurance exercise performance: a systematic review and meta-analysis of randomised controlled trials
d'Unienville NMA, Blake HT, Coates AM +1 more
No effect on exercise performance following consumption of foods rich in L-citrulline was identified (SMD=-0.03, p=0.24).
L-citrulline-malate influence over branched chain amino acid utilization during exercise
Sureda A, Cordova A, Ferrer MD +3 more
Oral L-citrulline supplementation raises plasma L-arginine concentration and augments NO-dependent signalling.
Effect of L-Citrulline Supplementation on Blood Pressure: a Systematic Review and Meta-Analysis of Clinical Trials
Barkhidarian B, Khorshidi M, Shab-Bidar S +1 more
L-citrulline supplementation significantly reduced systolic blood pressure.
Effect of oral L-citrulline on brachial and aortic blood pressure defined by resting status: evidence from randomized controlled trials
Mahboobi S, Tsang C, Rezaei S +1 more
Effects on resting brachial blood pressure were small and largely non-significant.
Oral L-citrulline supplementation improves erection hardness in men with mild erectile dysfunction
Cormio L, De Siati M, Lorusso F +4 more
Erection hardness score improved to normal in 50% of men on L-citrulline versus 8.3% on placebo.
Beetroot juice supplementation, plasma nitrite and exercise performance: a systematic review and meta-analysis
Hoon MW, Johnson NA, Chapman PG +1 more
Nitrate elevated plasma nitrite and improved time-to-exhaustion
Dietary nitrate reduces the oxygen cost of exercise: a systematic review and meta-analysis
Pawlak-Chaouch M, Boissiere J, Gamelin FX +3 more
Nitrate significantly reduced the oxygen cost of submaximal exercise in non-elite participants
Safety Information
Potential Side Effects
Very safe and well tolerated. Rarely causes digestive upset. More effective than arginine for raising blood arginine levels. Typical dose 6-8g L-citrulline or 8-10g citrulline malate 30-60 minutes pre-workout. No loading required.
Contraindications
Concurrent nitrates or PDE5 inhibitors, symptomatic hypotension, and severe renal impairment. Insufficient data in pregnancy and lactation.
Drug Interactions
- PDE5 inhibitors (sildenafil, tadalafil) — additive hypotension
- Nitrates — significant hypotension risk
- Antihypertensives — additive blood pressure lowering
- Anticoagulants — theoretical additive effect via nitric oxide and platelet function
Pregnancy & Breastfeeding
Pregnancy: insufficient_data
Breastfeeding: insufficient_data
Dosage Guidelines
Dosage Used in Studies
3000-8000 mg
Best Time to Take
60 minutes pre-workout, or once daily for cardiovascular use
Best Form
Pure L-citrulline for blood pressure; citrulline malate 2:1 for training volume
Bioavailability
Well absorbed and not subject to first-pass arginase degradation, giving it substantially higher effective bioavailability as an arginine source than arginine itself. Plasma arginine peaks around 60-90 minutes.
Forms Compared
L-citrulline (pure)
Citrulline malate 2:1
Watermelon extract
Arginine plus citrulline
Food & Timing
On an empty stomach 60 minutes pre-training for performance; any time with or without food for daily cardiovascular use
Medical Disclaimer
The information provided on this website is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any supplement regimen.
Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.