Which is better, L-citrulline or L-arginine?

November 30, 2025 •

3 min read

While L-arginine is a direct precursor to nitric oxide, recent studies show that supplementing with L-citrulline is more effective at raising blood arginine levels than taking L-arginine directly. This superior bioavailability is the main reason many fitness and health experts favor L-citrulline over L-arginine for consistent results.

Quick Summary

This article compares the amino acids L-citrulline and L-arginine, detailing their distinct mechanisms for increasing nitric oxide production, and weighing their pros and cons for athletic performance, heart health, and erectile function. It highlights L-citrulline's better absorption and sustained effects.

Key Points

Superior Bioavailability: L-citrulline is more effectively absorbed and utilized by the body, leading to higher plasma arginine levels than supplementing with L-arginine directly.
Enhanced Nitric Oxide Production: As an indirect precursor, L-citrulline provides a sustained release of L-arginine, resulting in longer-lasting nitric oxide synthesis and improved blood flow.
Better Digestive Tolerance: Unlike L-arginine, L-citrulline avoids extensive first-pass metabolism, which reduces the risk of gastrointestinal side effects like diarrhea and bloating.
More Effective for Endurance: For athletic performance, L-citrulline's consistent effect on nitric oxide is more beneficial for promoting sustained energy, delayed fatigue, and better muscular recovery.
Potential for Combination: Taking both supplements can produce a synergistic effect, offering both a quick and prolonged boost to nitric oxide levels.

Understanding L-Citrulline and L-Arginine

L-citrulline and L-arginine are non-essential amino acids that play key roles in the body, particularly in the urea cycle and the production of nitric oxide (NO). Nitric oxide is a vasodilator, improving blood flow and circulation, which benefits athletic performance, cardiovascular health, and erectile function. The primary difference lies in their metabolism and how well they are absorbed as supplements.

The Challenge of L-Arginine

Oral L-arginine is largely broken down by gut and liver enzymes in a "first-pass metabolism" effect before reaching the bloodstream. This low bioavailability means large doses are needed for significant increases in plasma arginine, and these high doses can cause gastrointestinal side effects like nausea and diarrhea.

The Advantage of L-Citrulline

L-citrulline bypasses this first-pass metabolism, traveling to the kidneys where it is converted to L-arginine. This leads to a more sustained increase in bloodstream L-arginine and thus higher, longer-lasting nitric oxide production. Research indicates L-citrulline raises plasma arginine levels more effectively than L-arginine supplementation. Its better absorption also contributes to improved tolerance and fewer digestive issues.

Impact on Specific Health Outcomes

Both amino acids increase NO, but their different metabolic routes affect their effectiveness. L-citrulline's sustained effect is often preferred for athletes seeking endurance and for cardiovascular health needing consistent NO levels. For mild-to-moderate erectile dysfunction, L-citrulline's better tolerance and prolonged effect make it a strong option.

L-Citrulline and L-Arginine Comparison Table


Feature	L-Citrulline	L-Arginine
Absorption/Bioavailability	High; bypasses gut and liver metabolism for better absorption.	Low; undergoes significant first-pass metabolism in the gut and liver.
Mechanism	Indirectly boosts nitric oxide production by converting to L-arginine in the kidneys.	Directly boosts nitric oxide production, but much is lost during digestion.
Effect Duration	Longer-lasting, sustained release of L-arginine into the bloodstream.	Shorter duration of effect due to poorer absorption.
Gastrointestinal Tolerance	Generally well-tolerated with fewer digestive side effects.	May cause digestive issues like nausea or diarrhea, especially at high doses.
Typical Dosage	3-8 grams daily, sometimes as citrulline malate.	2-6 grams daily, with higher doses increasing risk of side effects.
Athletic Performance	More effective for endurance and sustained energy during workouts.	Can provide a quicker, but less sustained, "pump" effect.
Cardiovascular Support	Offers more consistent and longer-lasting support for blood pressure and circulation.	Can acutely reduce blood pressure, but effects are less consistent over time.
Effect on NO Production	More reliably and effectively raises plasma arginine levels for nitric oxide synthesis.	Less effective at raising plasma arginine and nitric oxide due to poor absorption.

Can L-Citrulline and L-Arginine Be Combined?

Some evidence suggests combining both may create a synergistic effect, using complementary pathways for a quick and sustained nitric oxide boost.

Choosing the Right Supplement for Your Needs

The choice depends on individual goals and response. L-citrulline is generally better for most, especially those with digestive sensitivity or needing consistent effects for performance or cardiovascular health, due to its higher bioavailability. L-arginine might suit those wanting a rapid but short-lived NO increase, but high-dose side effects are a concern. Combining them may offer a balance.

In summary, while both L-citrulline and L-arginine benefit nitric oxide production, L-citrulline's metabolism offers superior bioavailability and consistency, making it the more effective choice for most individuals. For more on the conversion process, the National Institutes of Health has relevant studies. Consulting a healthcare professional before starting any new supplement is advised.

Conclusion: The Clear Winner is L-Citrulline for Most

L-citrulline is generally the superior supplement for increasing nitric oxide. Its high bioavailability, long-lasting effects, and better tolerance outweigh L-arginine's poor absorption and potential high-dose side effects. Although L-arginine directly precedes nitric oxide, its metabolic limitations make it less efficient for sustained blood arginine levels. L-citrulline offers a more reliable solution for athletes, those with cardiovascular concerns, and individuals with mild erectile dysfunction. A combination can be considered for a balanced effect, but L-citrulline alone is highly effective.

Benefits associated with L-citrulline include:

Improved Blood Flow: Supports healthy circulation via increased nitric oxide.
Enhanced Athletic Performance: Improves endurance, reduces fatigue, and boosts exercise efficiency through better oxygen delivery.
Cardiovascular Support: Helps lower blood pressure, aiding heart health.
Erectile Function Support: Improves blood flow to help manage mild-to-moderate erectile dysfunction.
Reduced Muscle Soreness: Assists in removing exercise waste products like ammonia, promoting faster recovery.
Better Digestive Tolerance: More efficiently absorbed with fewer gastrointestinal issues compared to L-arginine.

Frequently Asked Questions

L-arginine is a direct precursor to nitric oxide (NO) but has poor bioavailability due to significant breakdown in the gut and liver. L-citrulline bypasses this process, converting efficiently into L-arginine in the kidneys, leading to a more effective and sustained increase in NO production.

L-citrulline is generally considered better for athletic performance and muscle pumps due to its superior bioavailability and sustained effect on nitric oxide levels. It helps with endurance and recovery, while L-arginine provides a shorter-lived effect.

L-citrulline is generally well-tolerated and associated with fewer gastrointestinal side effects compared to L-arginine. Some people may experience mild digestive discomfort, but this is less common.

Yes, some research suggests that combining L-citrulline and L-arginine can have a synergistic effect, providing both a rapid boost and sustained release of nitric oxide. It is always best to consult a healthcare professional before combining supplements.

Due to its longer-lasting and more consistent effect on blood pressure and circulation, L-citrulline is often the better choice for sustained cardiovascular support. It more reliably boosts nitric oxide levels, which helps relax and widen blood vessels.

Some studies indicate that oral L-citrulline supplementation can improve erection hardness in men with mild-to-moderate erectile dysfunction. It is often considered a safer, though less potent, alternative to traditional ED drugs and is psychologically well-accepted by patients.

Citrulline malate is a common form of L-citrulline used in supplements, which combines L-citrulline with malic acid. The addition of malic acid may offer benefits for energy production and muscle soreness, in addition to L-citrulline's effects.