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Supplement · amino_acid

Citrulline

Quick read: L-Citrulline is a non-essential alpha-amino acid, which, unlike proteinogenic amino acids, is not incorporated into proteins.

Quick facts · L-Citrulline

Dose
4 g
Per day
6 g
Timing
First half of the day · Between meals · Daily
Course
120 days + break 40 days
Strongest effect
Blood Flow ImprovementVery highTheoretical
Scientific background
L-Citrulline is a non-essential alpha-amino acid, which, unlike proteinogenic amino acids, is not incorporated into proteins. It is endogenously synthesized as a key intermediate in the urea cycle, having crucial importance for ammonia detoxification, and is also abundantly present in watermelons. Upon ingestion, L-Citrulline is efficiently absorbed and significantly converted to L-arginine, primarily in the kidneys. This conversion is central because L-arginine is the direct substrate for nitric oxide synthase (NOS) — the enzyme responsible for producing nitric oxide (NO). NO is a powerful vasodilator, promoting the relaxation of blood vessels and thereby enhancing blood flow and nutrient delivery to various tissues. Furthermore, Citrulline aids in the removal of ammonia—a metabolic byproduct that accumulates during intense physical activity and contributes to fatigue. Consequently, L-Citrulline supplementation is actively researched for its potential to improve exercise performance, especially in endurance and strength training, by enhancing muscle oxygenation and reducing metabolic waste. Its role in supporting cardiovascular health through improved vascular function and in conditions like erectile dysfunction is also an area of active research, considering its profound impact on the NO pathway. Future studies continue to explore its therapeutic potential across diverse physiological contexts.

Form & dosage

Single dose
4 g
Daily
6 g
Course
120 days
Break
40 days
Timing
First half of the day · Between meals · Daily
How we rate evidence

Probability — how likely the effect is to show up

  • Very high
  • High
  • Medium
  • Low

Evidence — where the data comes from

  • Scientific Meta-analyses and randomized trials
  • Clinical Clinical trials and practice
  • Animal research Animal studies
  • People reports User reports and anecdotes
  • Theoretical Mechanistic reasoning, not yet tested

Effects

Very high probability(3)

  • Blood Flow Improvementbodytheoretical

    Citrulline enhances blood flow by increasing the body's production of nitric oxide, a powerful vasodilator. This widens blood vessels, ensuring better oxygen and nutrient delivery to working muscles and other tissues, leading to improved performance and overall vitality.

  • Physical Endurance Increasebodytheoretical

    Citrulline boosts physical endurance by enhancing oxygen delivery to muscles and improving the clearance of metabolic byproducts like ammonia. This allows for longer, more intense workouts, reducing fatigue during prolonged exertion.

  • Workout Efficiency Enhancementbodytheoretical

    Citrulline enhances overall workout efficiency by boosting endurance, reducing fatigue, and improving recovery. This enables more productive training sessions, leading to better adaptations and progress in strength and muscle gains.

High probability(4)

  • Cardiovascular System Supporthealththeoretical

    Citrulline supports overall cardiovascular health by improving endothelial function and blood flow through increased nitric oxide synthesis. This helps maintain vessel elasticity and efficient circulation, contributing to a healthy heart and vascular system.

  • Normal Blood Pressure Supporthealththeoretical

    By increasing nitric oxide production, Citrulline helps relax and widen blood vessels, contributing to the maintenance of healthy blood pressure levels. This is particularly beneficial for individuals with mild elevations, promoting cardiovascular well-being.

  • Muscle Recovery Accelerationbodyclinical

    Through enhanced blood flow, Citrulline accelerates muscle recovery by facilitating nutrient delivery and efficient removal of waste products post-exercise. Users often report reduced muscle soreness and quicker readiness for the next training session.

  • Fatigue Reductionpsycheclinical

    By optimizing blood flow and assisting in the removal of fatigue-inducing metabolites such as ammonia, Citrulline helps reduce both physical and mental tiredness, especially during strenuous activity. It can lead to sustained energy and alertness.

Medium probability(3)

  • Physical Strength Increasebodyclinical

    While not a direct strength booster, Citrulline's ability to reduce fatigue and enhance endurance can indirectly contribute to increased physical strength. Users may find they can perform more repetitions or sustain higher intensities, leading to progressive overload and strength adaptations.

  • Cellular Energy Supporthealthclinical

    Citrulline supports cellular energy production by optimizing oxygen utilization and, especially when combined with malic acid (as Citrulline Malate), directly contributing to the Krebs cycle. This provides the fundamental fuel cells need for optimal function.

  • Erectile Function Supporthealthclinical

    Citrulline can support erectile function by improving blood flow to the penis through nitric oxide-induced vasodilation, similar to how certain medications work, though typically with a milder effect. This mechanism facilitates the physiological process of erection.

Low probability(1)

  • Increased Growth Hormone Releasehealthclinical

    While some theoretical pathways link Citrulline (via Arginine) to growth hormone release, practical, noticeable increases from typical supplement doses are very low for most users. It's more of a minor theoretical possibility than a primary, consistently felt effect.

Side effects

Low probability(2)

  • Digestive Discomforthealthpeople_reports

    Some users, particularly when taking higher doses or if sensitive, might experience general stomach upset like mild cramps, bloating, or a feeling of heaviness. This typically resolves by reducing the dose or taking it with food.

  • Nauseahealthpeople_reports

    Initial doses or higher intakes of Citrulline can sometimes lead to a feeling of queasiness or nausea, which is often transient. Taking the supplement with a small meal or spreading doses can help mitigate this.

Low probability(4)

  • Hypotensionhealththeoretical

    Citrulline increases nitric oxide, which dilates blood vessels and can lead to a reduction in blood pressure. While often beneficial, it can rarely cause symptomatic low blood pressure, especially in individuals already prone to hypotension.

  • Diarrheahealthpeople_reports

    While uncommon at recommended doses, very high intakes of Citrulline may cause loose stools or diarrhea due to its osmotic properties in the gut. This is typically a dose-dependent effect.

  • Headachehealthpeople_reports

    Some individuals may experience a mild headache, likely related to the increased nitric oxide production causing vasodilation and changes in blood flow. This effect is rare and usually mild.

  • Dizzinessmindpeople_reports

    A feeling of lightheadedness or dizziness can occasionally occur, particularly when starting Citrulline or if sensitive to its blood pressure-lowering effects due to vasodilation.

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