Arginine-precursor amino acid · Fact sheet
L-citrulline
Also known as Citrulline
L-citrulline is an amino acid studied for nitric-oxide-related physiology and exercise. Small studies give conflicting performance results, and higher arginine levels do not automatically mean better athletic outcomes.
What is L-citrulline?
Citrulline can be converted to arginine, a substrate for nitric oxide production.
Pure L-citrulline and citrulline malate are different formulations; total malate-blend mass is not pure citrulline mass.
Benefits & claims
Interest in L-citrulline spans recovery, metabolism. Study findings apply to the named formulation and population.
What the evidence supports
- The cycling study found approximately 1.5% faster completion on a four-kilometer test.
- A biochemical increase in arginine did not establish broad improvement across sports or training levels.
- Combination studies cannot isolate the effect of citrulline alone.
Research areas
- Formulation-specific human outcomes
- Mechanistic research
Dosage & frequency
Human study contextThis is an exposure from a named human study, not a generally established treatment or enhancement regimen.
Four-kilometer cycling crossover study
22 healthy trained males
- Amount
- 2.4 g L-citrulline
- Frequency
- Daily for seven days, followed by 2.4 g one hour before testing on day eight
- Route studied or labeled
- Oral
This is pure L-citrulline, not an equal mass of citrulline malate. A single specialized cycling test does not establish benefit across sports.
How to read these amounts
An approved regimen belongs to a specific product, indication, and population. A study regimen describes what researchers tested; it does not establish a prescription or a safe self-use protocol. Products, routes, and formulations are not interchangeable. A prescriber uses the full label and individual clinical circumstances.
Personal accounts may describe amounts, schedules and outcomes beyond clinical research. They do not establish a regimen. Read the reported experiences
Formulations, interactions & practical context
- Identity and pharmacology
- Citrulline can be converted to arginine, a substrate for nitric oxide production.
Formulation differences
- Pure L-citrulline and citrulline malate are different formulations; total malate-blend mass is not pure citrulline mass.
Interactions & precautions
- The reviewed sources do not establish a comprehensive human interaction profile for this exact substance or combination.
What is still unresolved
- Reproducibility in larger independent trials
- Long-term outcomes and adverse effects
- Equivalence of different preparations and interaction profiles
Side effects & risks
- Short exercise trials do not establish chronic safety for all cardiovascular conditions or medication combinations.
- Product ratios and other ingredients can alter exposure and make both efficacy and tolerability uncertain.
This is a summary of the cited evidence, not a complete product label. A lack of human safety data does not establish safety.
Clinical research
Early human evidenceA 22-man crossover trial found a small cycling-time improvement. NIH summarizes heterogeneous studies with conflicting performance outcomes.
Studies
22 trained men in a short crossover cycling trial.
Different clinical context: congenital-heart-surgery trial.
Personal experiences
Reports describe what someone noticed. They cannot establish cause, typical results, or how often a side effect happens. Amounts and schedules describe the individual account, not an effective or safe dose. Product identity and strength may be unverified, and missing details are left explicit.
No attributable personal accounts were found in the sources reviewed.
Approval status
No FDA-approved L-citrulline drug indication is established for the supplement uses discussed here. Supplement availability is not FDA approval of efficacy or safety.
No FDA-approved product for this entry
Approval covers the labeled product, use and population. A trial phase does not establish success; a stopped program is not ongoing research.
- Oral L-citrulline supplementation enhances cycling time trial performance in healthy trained men: Double-blind randomized placebo-controlled 2-way crossover study.
- Nitric oxide precursors and congenital heart surgery: a randomized controlled trial of oral citrulline.
- NIH ODS: exercise and athletic-performance supplements
Open questions
- Reproducibility in larger independent trials
- Long-term outcomes and adverse effects
- Equivalence of different preparations and interaction profiles
Summary
Combination studies cannot isolate the effect of citrulline alone.
Sources
Medical evidence and regulatory sources are listed here. Personal reports are linked separately in the experiences section.
- pubmedOral L-citrulline supplementation enhances cycling time trial performance in healthy trained men: Double-blind randomized placebo-controlled 2-way crossover study.
22 trained men in a short crossover cycling trial.
- pubmedNitric oxide precursors and congenital heart surgery: a randomized controlled trial of oral citrulline.
Different clinical context: congenital-heart-surgery trial.
- nihNIH ODS: exercise and athletic-performance supplements
Ingredient-specific efficacy, tolerability and evidence limits for performance supplements.