L-Citrulline
L-Citrulline (Citrulline Malate)
L-Citrulline is a non-essential amino acid found naturally in watermelon and produced endogenously in the urea cycle. It is widely used as a sports performance and cardiovascular supplement, primarily to enhance nitric oxide (NO) production, improve exercise endurance, reduce muscle soreness, and support healthy blood pressure. Citrulline malate is the most common commercial form, combining L-Citrulline with malic acid to potentially amplify ergogenic effects.
Mechanism of Action
L-Citrulline is converted in the kidneys to L-Arginine, which serves as the direct substrate for nitric oxide synthase (NOS) enzymes that produce nitric oxide from arginine and oxygen. This NO-mediated vasodilation increases blood flow, enhances oxygen and nutrient delivery to skeletal muscle, and reduces the oxygen cost of exercise. Additionally, citrulline participates in the urea cycle to facilitate ammonia clearance, and malic acid (in citrulline malate) supports the Krebs cycle, contributing to ATP resynthesis and reduced fatigue.
Evidence by Health Goal(18 goals)
Dosing Protocols
45-60 minutes before exercise on training days; any time on rest days
For citrulline malate 2:1, use 6-8g to deliver approximately 4g of L-Citrulline. Pure L-Citrulline at 3-6g is roughly equivalent. Doses above 10g have been associated with increased gastrointestinal discomfort without additional benefit.
Once in the morning and once 45-60 minutes before exercise or with evening meal
Split-dosing protocol used for cardiovascular and blood pressure support rather than acute exercise performance. Consistent daily use is important for sustained effects on vascular function and NO bioavailability.
Safety & Side Effects
L-Citrulline has a well-established safety profile and is considered safe for healthy adults at recommended doses, with no significant toxicity observed in clinical studies up to 15g. Individuals with low blood pressure, those taking antihypertensive medications, or those with kidney disorders should consult a physician before use, as citrulline can further reduce blood pressure and increases renal arginine production.
Possible Side Effects
- !Gastrointestinal discomfort, bloating, or loose stools at doses above 10g
- !Nausea, particularly when taken on an empty stomach at high doses
- !Stomach cramping when combined with other high-dose pre-workout stimulants
- !Headache, potentially due to pronounced vasodilation at initial use
- !Hypotension (low blood pressure), especially at higher doses in sensitive individuals
- !Heartburn or acid reflux in susceptible individuals
- !Mild diuretic effect at higher doses
Interactions
- -Can significantly lower blood pressure - use with caution when combined with antihypertensive medications (e.g., ACE inhibitors, ARBs, calcium channel blockers)
- -May potentiate the effects of phosphodiesterase-5 (PDE5) inhibitors such as sildenafil (Viagra) or tadalafil, leading to dangerous hypotension - contraindicated
- -Additive vasodilatory effect when combined with nitrate-containing medications or supplements (e.g., nitrates for angina)
- -May enhance the performance and blood-flow effects of other NO-boosting supplements such as L-Arginine or beetroot extract - reduce individual doses to avoid hypotension
- -Theoretically may affect ammonia metabolism in individuals with urea cycle disorders - avoid without medical supervision in this population
Cost & Where to Buy
Bulk powder is the most cost-effective form, typically $15-25/month for quality citrulline malate. Branded pre-formulated capsules or premium sports nutrition blends can push costs to $35-40/month. Pure L-Citrulline powder is generally comparable in price to citrulline malate by weight but requires lower doses.
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