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Heart/Performance

L-Citrulline

Nitric oxide–supporting amino acid that may modestly improve blood flow, blood pressure, and exercise tolerance in adults.

L-Citrulline
57
score
C
evidence
Caution
risk

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Use with caution

This supplement may interact with medications, medical conditions or sensitive populations. Review safety before use.

Quick Take

Worth considering for modest blood-flow support or hard training, but the effects are real rather than dramatic.

L-citrulline is a nonessential amino acid found mainly in watermelon. After absorption it is converted to arginine, which can increase nitric oxide production and relax blood vessels. Human studies suggest modest benefits for systolic blood pressure, vascular function, exercise performance, and post-exercise recovery, with possible benefit in mild erectile dysfunction. It tends to help most in adults with high-normal blood pressure, lower vascular function, or demanding exercise.

Potential benefits

01
Lowers systolic BP modestly
02
Improves exercise performance
03
May improve vascular function
04
May reduce muscle soreness
05
May improve erectile function
06
May reduce perceived fatigue

Protocol

Amount
3-6 g
Frequency
Once daily, or 30-60 minutes before exercise
When
Between meals for vascular use; 30-60 minutes before activity for acute performance effects.

Onset Time

1-2 hours acutely; 2-8 weeks for blood pressure effects

Who Should Consider

Adults with high-normal or mildly elevated blood pressure
Adults 40+ noticing reduced exercise performance
People who get GI upset from L-arginine
People doing interval training or strenuous workouts
Men with mild vascular erectile symptoms

Food Sources

  • Watermelon flesh (~200-300 mg per 100 g, highly variable)
  • Watermelon juice (~500-900 mg per 500 mL, variety-dependent)

How It Works

L-citrulline bypasses much of the intestinal and liver breakdown that limits oral arginine. The kidneys convert it to arginine, which raises nitric oxide synthesis, widens blood vessels, improves blood flow, and may reduce ammonia buildup during exercise.

Updated 5/19/2026

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