# Citrulline

**Canonical URL:** https://ingredients.hermeticasuperfoods.com/ingredients/citrulline
**Data Source:** Hermetica Superfoods Ingredient Encyclopedia
**Updated:** 2026-04-04
**Evidence Score:** 2 / 10
**Category:** Compound
**Also Known As:** L-Citrulline, 2-amino-5-ureidopentanoic acid, Citrulline malate, N5-Carbamoyl-L-ornithine, Cit, L-2-Amino-5-ureidovaleric acid

## Overview

Citrulline is a non-essential amino acid that serves as a key precursor to arginine and, subsequently, nitric oxide (NO) via the urea cycle and the arginine-NO synthase pathway. It enhances vascular function, supports muscle performance, and may benefit critically ill patients by improving hemodynamic stability and endothelial signaling.

## Health Benefits

• May reduce postoperative pulmonary hypertension in pediatric patients, with elevated citrulline and arginine levels observed (PMID: 16798303).
• Improves ventilator-free days and survival in critically ill patients (PMID: 36620736).
• Enhances microvascular [endothelial function](/ingredients/condition/heart-health) and muscle strength (PMID: 40944179).
• Potential positive impact on lipid profile and [inflammation](/ingredients/condition/inflammation) markers like hs-CRP (PMID: 36620736).
• Improves blood flow and reduces vascular stiffness by enhancing nitric oxide production (PMID: 40944179).

## Mechanism of Action

Citrulline is converted to arginine in the kidneys via argininosuccinate synthetase and argininosuccinate lyase, bypassing hepatic first-pass [metabolism](/ingredients/condition/weight-management) that limits direct arginine supplementation. Arginine then serves as the substrate for endothelial nitric oxide synthase (eNOS), catalyzing the production of nitric oxide, which activates soluble guanylate cyclase to increase cyclic GMP and promote vascular smooth [muscle relaxation](/ingredients/condition/sleep). Additionally, citrulline participates in the urea cycle, reducing ammonia accumulation and potentially attenuating exercise-induced fatigue by modulating AMPK and mTORC1 signaling pathways.

## Clinical Summary

A study in pediatric cardiac surgery patients (PMID: 16798303) found that citrulline supplementation significantly elevated plasma citrulline and arginine levels, reducing the incidence of postoperative pulmonary hypertension. A randomized controlled trial in critically ill adults (PMID: 36620736) demonstrated that citrulline supplementation improved ventilator-free days and 28-day survival compared to placebo. Smaller trials and meta-analyses in healthy adults and athletes report improvements in microvascular [endothelial function](/ingredients/condition/heart-health) and muscle strength, particularly with L-citrulline doses of 3–8 g/day or citrulline malate at 6–8 g/day pre-exercise. Overall evidence is moderate-to-promising but larger, well-powered RCTs are still needed, especially for performance and [longevity](/ingredients/condition/longevity) endpoints.

## Nutritional Profile

Citrulline (C₆H₁₃N₃O₃, MW 175.19 g/mol) is a non-essential alpha-amino acid and key intermediate in the urea cycle. It is not one of the 20 standard proteinogenic amino acids and is therefore not incorporated into proteins during translation. Key nutritional and biochemical details: • **Endogenous synthesis**: Produced primarily in enterocytes of the small intestine from glutamine and proline via ornithine; also generated as a byproduct of nitric oxide synthase (NOS) converting arginine to nitric oxide (NO). • **Dietary sources**: The richest natural dietary source is watermelon (Citrullus lanatus), containing approximately 1.1–4.7 mg/g fresh weight (flesh) and up to 24 mg/g in rind; also found in smaller amounts in cucumbers, pumpkins, bitter melon, and other cucurbits. • **Supplement forms**: Commonly available as L-citrulline (free-form) or citrulline malate (typically 2:1 ratio of citrulline to malic acid); typical supplemental doses range from 3–8 g/day of L-citrulline or 6–8 g/day of citrulline malate. • **Bioactive role**: Serves as the most efficient oral precursor to L-arginine; oral citrulline bypasses hepatic first-pass [metabolism](/ingredients/condition/weight-management) (unlike oral arginine, which is substantially catabolized by hepatic arginase), resulting in superior plasma arginine elevation — approximately 1.5–2× greater increase in plasma arginine compared to equimolar oral arginine supplementation. • **Bioavailability**: Oral bioavailability is high (>80%); absorbed in the small intestine, transported to the kidneys where it is converted to arginine via argininosuccinate synthase (ASS) and argininosuccinate lyase (ASL). Peak plasma citrulline levels occur approximately 40–60 minutes post-ingestion. • **Caloric/macronutrient contribution**: Negligible caloric value at supplemental doses (~4 kcal/g as an amino acid, but doses are small); contains no vitamins, minerals, fiber, or fat. Each molecule provides 3 nitrogen atoms (23.99% nitrogen by mass), contributing to nitrogen balance. • **Plasma reference range**: Normal circulating plasma citrulline levels are approximately 20–40 µmol/L in healthy adults; levels below 10 µmol/L may indicate intestinal failure or reduced enterocyte mass. • **Related bioactive metabolites**: Directly feeds into arginine → NO pathway, supporting nitric oxide-dependent vasodilation; also contributes to polyamine synthesis and creatine biosynthesis indirectly via arginine. • **No known essential micronutrient content**: Pure citrulline contains no vitamins or minerals; watermelon-derived citrulline co-occurs with lycopene, vitamin C (~8.1 mg/100g), potassium (~112 mg/100g), and other phytonutrients.

## Dosage & Preparation

Clinically studied dosage ranges include 1.9 g/m² per dose in postoperative settings, daily supplementation over 7 days in critically ill patients, and up to 24 g/day in tolerance studies. Consult a healthcare provider before starting any new supplement.

## Safety & Drug Interactions

Citrulline is generally well tolerated at doses up to 15 g/day, with the most commonly reported side effects being mild gastrointestinal discomfort, nausea, or diarrhea at higher doses. Because citrulline raises nitric oxide and arginine levels, it may potentiate the hypotensive effects of PDE5 inhibitors (e.g., sildenafil, tadalafil) and nitrate-based medications, and concurrent use should be approached cautiously. Individuals with rare urea cycle disorders, particularly argininosuccinate synthetase deficiency, should avoid citrulline supplementation without medical supervision. Safety data in pregnancy and lactation are insufficient, so use during these periods is not recommended without physician guidance.

## Scientific Research

Clinical trials have shown citrulline's potential benefits in various health conditions. Notable studies include a pediatric study on postoperative pulmonary hypertension (PMID: 16798303) and an RCT on critical illness and mechanical ventilation (PMID: 36620736). A meta-analysis reviewed the heterogeneity in trial designs for [blood pressure](/ingredients/condition/heart-health) interventions (PMID: PMC11053694).

## Historical & Cultural Context

The research does not indicate any traditional use of citrulline in historical medicine systems. Its use as a concentrated supplement appears to be a modern development, with natural presence in foods like watermelon.

## Synergistic Combinations

L-arginine, watermelon extract, nitric oxide boosters, beetroot powder, taurine

## Known Interactions

| Substance | Severity | Summary | URL |
|---|---|---|---|
| Tyrosine | SAFE | 🟢 SAFE — Citrulline and Tyrosine can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/tyrosine |
| Phosphatidylserine | SAFE | 🟢 SAFE — Citrulline and Phosphatidylserine can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/phosphatidylserine |
| Bacopa Monnieri | SAFE | 🟢 SAFE — Citrulline and Bacopa Monnieri can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/bacopa-monnieri |
| Mucuna Pruriens | SAFE | 🟢 SAFE — Citrulline and Mucuna Pruriens can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/mucuna-pruriens |
| Dapagliflozin | SAFE | 🟢 SAFE — Citrulline and Dapagliflozin can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/dapagliflozin |
| Sitagliptin | SAFE | 🟢 SAFE — Citrulline and Sitagliptin can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/sitagliptin |
| Pioglitazone | SAFE | 🟢 SAFE — Citrulline and Pioglitazone can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/pioglitazone |
| Linagliptin | SAFE | 🟢 SAFE — Citrulline and Linagliptin can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/linagliptin |
| Telmisartan | SAFE | 🟢 SAFE — Citrulline and Telmisartan can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/telmisartan |
| Olmesartan | SAFE | 🟢 SAFE — Citrulline and Olmesartan can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/olmesartan |
| Diltiazem | SAFE | 🟢 SAFE — Citrulline and Diltiazem can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/diltiazem |
| Nifedipine | SAFE | 🟢 SAFE — Citrulline and Nifedipine can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/nifedipine |
| Cephalexin | SAFE | 🟢 SAFE — Citrulline and Cephalexin can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/cephalexin |
| Trimethoprim-Sulfamethoxazole | SAFE | 🟢 SAFE — Citrulline and Trimethoprim-Sulfamethoxazole can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/trimethoprim-sulfamethoxazole |
| Nitrofurantoin | SAFE | 🟢 SAFE — Citrulline and Nitrofurantoin can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/nitrofurantoin |
| Clindamycin | SAFE | 🟢 SAFE — Citrulline and Clindamycin can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/clindamycin |
| Methylprednisolone | SAFE | 🟢 SAFE — Citrulline and Methylprednisolone can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/methylprednisolone |
| Budesonide | SAFE | 🟢 SAFE — Citrulline and Budesonide can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/budesonide |
| Tacrolimus | SAFE | 🟢 SAFE — Citrulline and Tacrolimus can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/tacrolimus |
| Atomoxetine | SAFE | 🟢 SAFE — Citrulline and Atomoxetine can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/atomoxetine |

## Frequently Asked Questions

### What is the difference between L-citrulline and citrulline malate?

L-citrulline is the pure amino acid form, while citrulline malate combines L-citrulline with malic acid in a 2:1 ratio. Malic acid participates in the Krebs cycle and may independently reduce fatigue, though most sports studies use citrulline malate at 6–8 g; to match equivalent L-citrulline content, approximately 3–4 g of pure L-citrulline is needed.

### How much citrulline should I take for exercise performance?

Most clinical trials supporting improved muscle endurance and strength use citrulline malate at 6–8 g taken 60 minutes before exercise, delivering roughly 3–4 g of active L-citrulline. For pure L-citrulline, doses of 3–6 g pre-workout are commonly studied, with higher doses up to 8 g used in some trials examining blood pressure and NO output.

### Does citrulline lower blood pressure?

Citrulline can modestly reduce blood pressure by increasing nitric oxide production via eNOS, which relaxes vascular smooth muscle through cGMP elevation. A 2017 meta-analysis of 8 trials found that citrulline supplementation reduced systolic blood pressure by an average of approximately 4 mmHg, with effects more pronounced in hypertensive or pre-hypertensive individuals than in normotensive subjects.

### Is citrulline better than arginine for boosting nitric oxide?

Citrulline is generally considered more effective than oral arginine for raising plasma arginine and nitric oxide levels because it bypasses hepatic and intestinal arginase metabolism that rapidly degrades supplemental arginine before it reaches circulation. Studies show that 3 g of oral L-citrulline raises plasma arginine more effectively than an equivalent or even higher dose of oral arginine, making citrulline the preferred substrate for sustained NO synthesis.

### Can citrulline help with erectile dysfunction?

Small clinical evidence suggests L-citrulline may mildly support erectile function by increasing endothelial nitric oxide, which drives penile vasodilation via cGMP-mediated smooth muscle relaxation — the same pathway targeted by PDE5 inhibitors. A pilot RCT in men with mild erectile dysfunction found that 1.5 g/day of L-citrulline for one month significantly improved erection hardness scores compared to placebo, though effect sizes are substantially smaller than those observed with pharmaceutical PDE5 inhibitors.

### What does clinical research show about citrulline for critically ill patients?

Recent clinical studies demonstrate that citrulline supplementation improves ventilator-free days and overall survival rates in critically ill patient populations. Research indicates that citrulline helps support microvascular endothelial function, which is critical for oxygen delivery and tissue perfusion in patients with compromised cardiovascular status. These findings suggest potential therapeutic applications in intensive care settings, though dosing protocols are still being refined.

### Who should avoid citrulline supplementation or use it with caution?

While citrulline is generally well-tolerated, individuals taking nitrate-based medications or blood pressure medications should consult a healthcare provider before supplementing, as citrulline can have additive vasodilatory effects. People with severe kidney disease may need to adjust intake due to arginine metabolism pathways. Pregnant and nursing women should seek professional guidance before use, as safety data in these populations remains limited.

### Can citrulline improve inflammation markers and metabolic health?

Emerging research suggests citrulline may positively influence inflammatory markers such as hs-CRP (high-sensitivity C-reactive protein) and lipid profiles, contributing to improved cardiometabolic health. By enhancing nitric oxide production and endothelial function, citrulline supports vascular health, which is closely linked to systemic inflammation and cholesterol management. However, more large-scale human trials are needed to establish optimal dosing for these metabolic benefits.

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*Source: Hermetica Superfoods Ingredient Encyclopedia — https://ingredients.hermeticasuperfoods.com*
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