L-Citrulline is an amino acid that converts to arginine in the kidneys, raising nitric oxide levels and improving blood flow. Unlike supplemental arginine, citrulline bypasses the gut where arginine is mostly destroyed, making it a much more effective way to elevate arginine and nitric oxide. Evidence supports reductions in fatigue and modest endurance and strength benefits.
Citrulline reliably increases arginine and nitric oxide, improving blood flow and reducing exercise fatigue. Effects on strength and endurance are modest but consistent. Better value than arginine supplements for the same goal.
Each row grades the claimed effect by strength of human evidence, not mechanism or marketing.
Recognised as more effective than arginine for raising NO; included in ISSN and sports nutrition discussions as a reasonable pre-workout compound. Not a top-tier evidence compound but mechanistically credible.
Heavily marketed in pre-workout products, often in underdosed amounts (2–3 g vs the 6–8 g used in studies). The 'pump' sensation is real but often oversold as evidence of efficacy.
The pharmacokinetics are solid. The performance outcomes are real but modest. Most pre-workout products underdose it relative to research protocols.
Citrulline malate (citrulline bound to malate) is commonly used in studies; the malate may contribute independently to energy metabolism.
Effective dose is 6–8 g L-citrulline or 8–12 g citrulline malate — most pre-workout blends contain 2–3 g (sub-effective).
L-citrulline is found naturally in watermelon — but at very low concentrations; supplementation is necessary for research-equivalent doses.
Effect timing: peak blood arginine occurs around 60–90 minutes post-ingestion.
Unlike arginine, citrulline is not significantly broken down in the gut — this explains its superior efficacy via the arginine/NO pathway.
Mechanism is not outcome. Each mechanism is labelled by how far it has been validated in humans.
Citrulline is converted to arginine in the kidneys, bypassing the gut where supplemental arginine is rapidly degraded. This is why citrulline raises blood arginine more effectively than arginine itself.
Elevated arginine feeds the nitric oxide synthase (NOS) pathway, producing nitric oxide (NO) which relaxes blood vessel smooth muscle and improves blood flow to working muscle.
Citrulline is part of the urea cycle. Enhanced citrulline availability may improve ammonia clearance during intense exercise, reducing one source of exercise fatigue.
The malate in citrulline malate is a Krebs cycle intermediate that may support aerobic energy production directly — though how much this contributes at typical doses is debated.
Very well-tolerated at studied doses. No significant safety concerns identified in trials. Gastrointestinal discomfort at very high doses.
This page is educational and not medical advice. Discuss with a clinician if you take blood pressure medications or PDE5 inhibitors.
A small, curated set — not a literature dump. Each reference comes with a single-line takeaway.
8 g citrulline malate significantly increased repetitions to failure and reduced 48h muscle soreness vs placebo in trained men.
Confirmed that oral citrulline raises plasma arginine more effectively than oral arginine due to bypassing intestinal arginine metabolism.