L-Citrulline & Citrulline Malate

1. Generic or Accepted Substance Name & Classifications

Accepted Name: L-Citrulline & Citrulline Malate
Common Names, Synonyms & Classifications: L-Citrulline; 2-Amino-5-(carbamoylamino)pentanoic acid; L-Citrulline DL-Malate (2:1)
Section Classification: Group A — Evidence-Supported Sports Nutrition & Ergogenic Aids (PERF-A09)

2. Pharmacological Class

Non-Proteinogenic Urea-Cycle Amino Acid & Endogenous L-Arginine / Nitric Oxide (eNOS) Precursor

3. Mechanism of Action

Unlike oral L-arginine—which undergoes extensive (~40–70%) first-pass catabolism by intestinal and hepatic arginase—oral L-citrulline bypasses splanchnic extraction and is converted in renal proximal tubule cells via argininosuccinate synthase and argininosuccinate lyase into systemic L-arginine. This increases plasma L-arginine availability more effectively than oral L-arginine itself, supporting endothelial Nitric Oxide Synthase (eNOS)-mediated vasodilation and urea-cycle ammonia detoxification.

4. Proposed Performance or Endurance Effects (Pharmacological Effect vs Proven Athletic Outcome)

Pharmacological Effect: Elevates plasma L-arginine and ornithine concentrations and supports endothelial NO production. Proven vs Limited Athletic Performance Benefit: Meta-analyses show small, variable improvements (~1–2% or 1–2 extra repetitions to failure in multi-set high-intensity resistance exercise at 6–8 g Citrulline Malate taken ~60 min pre-exercise), but results in trained endurance time trials are inconsistent and weaker than those for dietary inorganic nitrate (beetroot) or caffeine. Unsupported Claims: Marketed 'muscle pump' claims do not equate to long-term myofibrillar hypertrophy or aerobic VO₂max gains.

5. Quality of Scientific Evidence

Evidence Assessment: Low to Moderate / Level B–C (Mixed clinical trial findings; superior to oral L-arginine for raising plasma arginine, but smaller and less consistent ergogenic effect size than Creatine, Caffeine, Nitrate, or Bicarbonate)

6. Approved Medical Uses (Where Applicable)

Used clinically in specialised metabolic centres for certain urea-cycle disorders (ornithine transcarbamylase [OTC] deficiency); otherwise regulated as a dietary supplement.

7. Sports-Related Uses, Misuse Patterns & Contamination Risks

Typically included in pre-workout powders (3–6 g L-citrulline or 6–8 g citrulline malate). Misuse includes combining high-dose citrulline with unapproved vasodilators or PDE-5 inhibitors, or assuming pre-workout blends containing citrulline are safe when they also contain undeclared stimulants.

8. Adverse Effects & Serious Safety Risks

Generally well tolerated at 3–8 g; occasional mild stomach discomfort or heartburn (primarily from the acidic malic acid component in citrulline malate) and mild orthostatic lightheadedness.

9. Contraindications & Precautions

Argininosuccinate synthase deficiency (citrullinaemia Type I), argininosuccinate lyase deficiency, severe hypotension, and concurrent nitrate/PDE-5 therapy.

10. Drug Interactions

Additive hypotensive effect when combined with antihypertensives, organic nitrates (Nitroglycerin, Isosorbide dinitrate), or PDE-5 inhibitors (Sildenafil, Tadalafil).

11. Clinical & Laboratory Monitoring Considerations

Monitor blood pressure in individuals on antihypertensive medications; verify product purity and absence of prohibited stimulants in multi-ingredient pre-workout blends.

12. Dependence, Misuse or Withdrawal Concerns

No dependence or withdrawal.

13. Regulatory & Legal Status in India (CDSCO / Drugs Rules / NDPS / FSSAI)

Permitted amino-acid/nutraceutical ingredient under FSSAI Nutraceutical and Sports Supplement Regulations in India.

14. Official WADA Prohibited-List Status

NOT PROHIBITED (Permitted at all times under the WADA Prohibited List).

15. Authoritative Source References & Date of Last Verification