L-Citrulline
L-Citrulline is an amino acid that enhances nitric oxide production, improving blood flow and exercise performance. It is commonly used as citrulline malate for pre-workout supplementation, with moderate evidence supporting its ergogenic effects.
Quick Verdict
A solid pre-workout ingredient for improving blood flow and exercise endurance, though not as well-proven as creatine.
If you train regularly and want improved muscular endurance and pump during workouts, citrulline malate at 6-8g pre-workout is a well-tolerated and reasonably supported option.
At a Glance
Dose
6-8g/day citrulline malate or 3-5g free-form L-citrulline
When to Take
30-60 minutes before exercise for acute performance benefits
Best Form
Citrulline malate 2:1
Evidence
61% avg
What It Is
L-Citrulline is a non-essential amino acid named after watermelon (Citrullus vulgaris), from which it was first isolated. Unlike many amino acids, citrulline is not incorporated into proteins but plays a critical role in the urea cycle and nitric oxide metabolism. It is available as free-form L-citrulline or as citrulline malate (bonded with malic acid). Citrulline malate is the most commonly used supplemental form in sports nutrition, often found in pre-workout formulas. The body converts citrulline to arginine in the kidneys, making it paradoxically more effective at raising blood arginine levels than supplemental arginine itself, which is extensively metabolized during first-pass liver metabolism.
How It Works
L-Citrulline works primarily by serving as a precursor to L-arginine, which is then converted to nitric oxide (NO) by nitric oxide synthase enzymes. This increased NO production causes vasodilation, relaxing blood vessel walls and improving blood flow to working muscles during exercise. Enhanced blood flow delivers more oxygen and nutrients while removing metabolic waste products like ammonia and lactate more efficiently. Citrulline also participates in the urea cycle, helping to clear ammonia — a fatigue-inducing byproduct of amino acid metabolism during exercise. The malate component in citrulline malate may additionally support aerobic energy production through its role in the tricarboxylic acid (TCA) cycle, though this mechanism is less well-established.
Evidence by Goal
exercise performance
Moderate evidence suggests citrulline supplementation can improve exercise performance, particularly in high-rep resistance training and endurance activities through enhanced blood flow.
blood flow
Citrulline reliably increases plasma arginine levels and enhances nitric oxide-mediated vasodilation, supporting improved blood flow during exercise.
Dosage & Usage
Standard Dose
6-8g/day citrulline malate or 3-5g free-form L-citrulline
Loading Protocol
No loading phase required
Timing
30-60 minutes before exercise for acute performance benefits
Best Form
Citrulline malate 2:1 (most studied) or free-form L-citrulline
📅 What to Expect
30-60 min
Acute nitric oxide boost. Improved blood flow and muscle pumps during exercise.
Day 1-7
Consistent pre-workout use yields reliable performance enhancement.
Week 2-4
Exercise endurance improvements of 5-15% in high-rep protocols.
Ongoing
No tolerance develops. Acute dosing continues to work consistently.
🎯 How to Know It's Working
Better muscle pumps during training
Less fatigue on high-rep sets
Slightly better endurance performance
If not working: If no effect after 1-2 weeks at 6-8g citrulline malate pre-workout, ensure you're taking it 30-60 min before training on empty stomach.
🏷️ Buying Guide
✓ Look For
- • L-Citrulline (not DL-citrulline malate unless 2:1)
- • 6-8g per serving for performance
- • Unflavored pure powder available
✗ Avoid
- • Citrulline malate underdosed below 6g
- • Pre-workouts with hidden citrulline amounts
🥗 Get It From Food
🛡️ Safety Profile
Common Side Effects
- • mild GI discomfort at high doses
⚠️ Contraindications
- 🚫 citrullinemia (rare genetic disorder)
💊 Drug Interactions
- • PDE5 inhibitors (additive blood pressure lowering)
- • nitrates
Long-Term Safety
No adverse effects reported in studies lasting up to 16 weeks at standard doses. As a naturally occurring amino acid found in food, long-term safety profile is considered excellent.
👥 Who Benefits Most
Best For
- ✓ resistance training athletes seeking pump and endurance
- ✓ individuals with mild blood pressure concerns
- ✓ older adults seeking cardiovascular support
Less Effective For
- — elite athletes already at peak cardiovascular conditioning
- — those seeking strength/power gains (more suited to creatine)
📚 Key Research
3 peer-reviewed studies supporting this supplement's effects.
Citrulline and exercise performance: a review of the literature
Trexler ET, Keith DS, Schwartz TA, et al. · Journal of the International Society of Sports Nutrition (2019)
Systematic review found that citrulline supplementation can enhance high-intensity exercise performance and reduce perceived exertion, though effect sizes are modest.
Acute L-citrulline supplementation and exercise performance
Bailey SJ, Blackwell JR, Lord T, et al. · Journal of Applied Physiology (2015)
L-citrulline supplementation increased plasma nitric oxide biomarkers and improved high-intensity exercise tolerance in healthy adults.
Citrulline malate supplementation and exercise performance: a review
Gonzalez AM, Trexler ET · Journal of Strength and Conditioning Research (2018)
Review confirmed that citrulline malate at doses of 6-8g can improve repetitions to failure during resistance exercise by approximately 10-15%.
💰 Cost & Forms
Estimated Monthly Cost
$15-25
🔗 Related Evidence Reviews
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