L-Citrulline: Benefits, Dosage, and What the Research Shows

A closer look at the amino acid behind the nitric oxide boost, and whether it actually helps performance.

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By the Ration Editorial Team · Reviewed against primary research · Updated July 13, 2026

L-citrulline is a non-essential amino acid, first identified from watermelon and named after the Latin word for the fruit, citrullus.

Unlike some amino acids, citrulline is not used much to build protein directly. Instead, it plays a starring role in a recycling loop that helps the body generate nitric oxide.

The body makes it naturally, but people also take it as a supplement, often as citrulline malate, paired with malic acid.

Nitric oxide is a signaling molecule that helps blood vessels widen, improving blood flow to muscles and organs.

You might expect that taking arginine directly, since arginine is the direct precursor to nitric oxide, would be the better strategy. Research suggests otherwise.

Oral arginine gets broken down heavily in the gut and liver before it reaches circulation. Citrulline bypasses this problem: it travels to the kidneys, where it is converted into arginine, resulting in higher blood arginine levels than taking arginine itself.^[4]

This is why citrulline is often described as a more efficient way to raise nitric oxide than arginine supplementation.^[4]

Nitric oxide production from citrulline has also been traced to specific tissues, including neurons, where citrulline staining is used as a marker of nitric oxide synthase activity.^[12][8]

Citrulline has one of the more consistent evidence bases among nitric oxide boosting supplements, particularly for endurance exercise.

• ↑VO2maxAHuman trials

  Research may raise VO2max · strong agreement · 6 studies

  View 5 studies on PubMed

  • Effects of Citrulline Supplementation on Different Aerobic Exercise Performance Outcomes: A Systematic Review and Meta-Analysis (2022)
  • Effects of Citrulline Supplementation on Exercise Performance in Humans: A Review of the Current Literature (2020)
  • Effect of food sources of nitrate, polyphenols, L-arginine and L-citrulline on endurance exercise performance: a systematic review and meta-analysis of randomised controlled trials (2021)
  • L-Citrulline Supplementation and Exercise in the Management of Sarcopenia (2021)
  • A critical review of citrulline malate supplementation and exercise performance (2021)
• ↑Nitric OxideAHuman trials

  Research may raise Nitric Oxide · strong agreement · 6 studies

  View 5 studies on PubMed

  • Effects of Quercetin and Citrulline on Nitric Oxide Metabolites and Antioxidant Biomarkers in Trained Cyclists (2025)
  • Glutamine and citrulline concentrations reflect nitric oxide synthesis in the human nervous system (2020)
  • Supplementation with Nitric Oxide Precursors for Strength Performance: A Review of the Current Literature (2023)
  • Citrulline and arginine utility in treating nitric oxide deficiency in mitochondrial disorders (2012)
  • Endogenous flux of nitric oxide: Citrulline is preferred to Arginine (2021)

A 2022 systematic review and meta-analysis found that citrulline supplementation improved several aerobic exercise performance outcomes, including time to exhaustion and measures related to VO2max.^[3]

An earlier 2020 review reached a similar conclusion, noting benefits for endurance-type exercise but more inconsistent results for single-session strength or power performance.^[9]

A broader 2021 meta-analysis comparing food sources of nitrate, polyphenols, arginine, and citrulline found that nitrate-rich foods had the most consistent endurance benefits, with citrulline showing a smaller but still positive effect.^[7]

For strength training specifically, a review of nitric oxide precursor supplements found the evidence for citrulline improving strength performance to be weaker and less consistent than its endurance effects.^[2]

A critical review of citrulline malate specifically noted that many positive findings come from studies with small sample sizes or short supplementation windows, and called for more rigorous trials before firm conclusions on strength outcomes.^[5]

In trained cyclists, a 2025 randomized trial testing citrulline alongside quercetin found favorable changes in nitric oxide metabolites and antioxidant markers, supporting the idea that citrulline's effects are at least partly tied to improved nitric oxide availability during exercise.^[1]

Outside of sport, citrulline has been studied in vascular function. One trial combining citrulline with watermelon extract reported improvements in arterial stiffness measures alongside modest performance benefits.^[10]

There is also early interest in clinical populations. A small trial in older adults with sarcopenia paired citrulline with exercise training and reported improvements in physical function measures.^[6]

In rare mitochondrial disorders involving nitric oxide deficiency, citrulline and arginine have been studied as ways to support vascular nitric oxide production, though this is a specialized clinical context rather than general use.^[11]

Watermelon, including the rind, is by far the richest dietary source of citrulline.

• Watermelon (flesh and rind)
• Cucumbers
• Muskmelon and other melons
• Pumpkin and squash
• Bitter gourd
• Garlic and onions (small amounts)

Getting the doses used in research, typically several grams, through food alone would require eating a large quantity of watermelon in one sitting, which is part of why supplemental forms are popular in sports nutrition.

Most performance studies use doses in the range of 6 to 8 grams of L-citrulline, or an equivalent amount of citrulline malate, taken roughly 1 hour before exercise.^[3][5][9]

Because citrulline malate combines citrulline with malic acid, the total gram amount on a label is not pure citrulline. Checking the actual citrulline content matters when comparing products.

There is no established dose for general health use outside of the exercise performance research, and most human trials are short term, lasting days to a few weeks.^[5]

Across the exercise trials, citrulline and citrulline malate are generally described as well tolerated at studied doses.^[2][3]

Mild digestive discomfort has been reported occasionally in some supplement trials, though this is not consistently seen across the literature.

Long-term safety data at high doses is limited, since most studies run for short durations tied to a single exercise test or a few weeks of training.^[5]

People with kidney conditions, low blood pressure, or those taking medications that affect blood vessel tone should be cautious, given citrulline's role in nitric oxide and blood flow regulation.

• Endurance athletes interested in VO2max and time-to-exhaustion performance, where evidence is strongest^[3][9]
• Cyclists and other aerobic sport participants, based on trial populations studied^[1][7]
• Older adults exploring exercise-based approaches to muscle function, in early clinical research^[6]
• People generally curious about nitric oxide and vascular function, with realistic expectations given mixed strength-training data^[2][5]

L-citrulline has a clearer, more efficient path to raising nitric oxide than arginine itself, and this shows up as a fairly consistent benefit for endurance exercise measures like VO2max.^[4][3]

The strength training evidence is thinner and more mixed, so expectations there should be more modest.^[2][5]

Watermelon remains the standout food source, though most research relies on concentrated supplemental doses rather than diet alone.