Benefits
Improved Exercise Performance
L-Citrulline increases nitric oxide production, which enhances blood flow, oxygen delivery, and nutrient uptake in muscles. This may boost endurance, reduce fatigue, and improve performance during high-intensity exercise, particularly in resistance training and aerobic activities.
Enhanced Muscle Recovery
By reducing ammonia buildup and muscle soreness, L-Citrulline may speed up recovery post-exercise, allowing for more consistent training.
Cardiovascular Health
L-Citrulline may lower blood pressure and improve arterial function by promoting vasodilation. Studies suggest it benefits individuals with hypertension or stiff arteries, supporting heart health.
Erectile Dysfunction (ED)
By boosting nitric oxide and blood flow, L-Citrulline may improve mild-to-moderate ED. Some studies show it’s as effective than a placebo, though more research is needed.
Immune System Support
Preliminary evidence suggests L-Citrulline may enhance immune function and reduce inflammation, potentially aiding overall health, but more studies are needed.
Potential Muscle Growth
L-Citrulline may indirectly support muscle protein synthesis by improving nutrient delivery and reducing fatigue, though evidence is less direct compared to other benefits.
Mechanism of action
Nitric Oxide (NO) Production
L-Citrulline is converted to L-arginine in the kidneys, which is then used by endothelial nitric oxide synthase (eNOS) to produce NO. This promotes vasodilation, improving blood flow to muscles, heart, and other tissues.
Ammonia Detoxification
L-Citrulline participates in the urea cycle, clearing ammonia (a fatigue-inducing byproduct) from the body, which enhances exercise endurance and recovery.
Antioxidant Effects
By increasing NO and improving blood flow, L-Citrulline reduces oxidative stress and supports nutrient delivery to tissues, aiding muscle repair and cardiovascular health.
Clinical trials
Randomized, double-blind, placebo-controlled trial (NCT02221843) in 22 trained male cyclists receiving 2.4 g L-citrulline vs placebo for 7 days, with 4-km cycling time trial. (J Int Soc Sports Nutr)
22 trained male cyclists. 7-day loading.
L-citrulline reduced 4-km time trial completion time by ~1.5% vs placebo and reduced subjective fatigue. Mechanism: increased plasma arginine → NO → vasodilation → improved muscle blood flow. Note: 1.5% performance improvement is meaningful in elite endurance contexts but small in absolute terms.
Pooled analysis of 8 randomized controlled trials (n=12-34 per study) through evaluating L-citrulline supplementation effects on blood pressure. (Curr Hypertens Rep)
Pooled across 8 clinical trials.
L-citrulline reduced systolic BP by ~7.5 mmHg and diastolic BP by ~4 mmHg vs placebo. Effect sizes modest but meaningful. Mechanism via citrulline-arginine-NO pathway. Should be considered adjunctive — not replacement for antihypertensive medications in established hypertension.
Multicenter clinical trial (NCT02864017) in 120 mechanically ventilated ICU patients with septic shock receiving enteral citrulline vs placebo. Outcomes: SOFA score Day 7. (Crit Care)
120 critically ill ICU patients with septic shock.
Primary endpoint negative: enteral citrulline did not improve SOFA score at Day 7 vs placebo. Important negative finding — extrapolating cardiovascular benefits to acute critical illness was not supported. Critical illness is metabolically very different from chronic CV applications.
Randomized controlled trial in 47 boys with Duchenne muscular dystrophy receiving L-citrulline + metformin vs placebo. Outcomes: motor function, dystrophin-related markers. (JAMA Netw Open)
47 boys with DMD.
Modest improvements in some motor function measures. Note: small trial; DMD treatment landscape has been transformed by gene therapies (delandistrogene moxeparvovec / Elevidys) and exon-skipping therapies (eteplirsen, golodirsen, viltolarsen) — supplemental citrulline + metformin has no role as primary therapy.
Randomized controlled trial in 24 men with mild ED (Erection Hardness Score 3) receiving L-citrulline (1.5 g/day) vs placebo. Outcomes: EHS, frequency of intercourse. (Urology)
24 men with mild ED. Small trial.
L-citrulline improved EHS and frequency of intercourse vs placebo. Critical caveat: very small trial (n=24); applies to mild ED only. PDE5 inhibitors remain first-line; citrulline at most adjunctive for mild cases.