Citrulline
The supplement behind the 'pump.' Citrulline boosts nitric oxide, improving blood flow, exercise performance, and potentially cardiovascular health. Here's how to use it.
Citrulline is an amino acid that your body converts to arginine, which then produces nitric oxide (NO) — a molecule that relaxes blood vessels and improves blood flow. It's better than supplementing arginine directly because citrulline bypasses first-pass liver metabolism.
Good for you if: You want better exercise performance, improved muscle pumps, or are interested in cardiovascular support through nitric oxide enhancement.
See the evidenceCommon side effects
- Mild stomach discomfort at high doses (>10 g)
- Very rare: mild headache from vasodilation
- No serious side effects in clinical studies
What does citrulline do?
When you take citrulline, your kidneys convert it to arginine, which then feeds into nitric oxide synthase (NOS) to produce nitric oxide (NO). NO relaxes smooth muscle in blood vessel walls, widening them and improving blood flow.
- Better exercise pumps — more blood flow to working muscles
- Improved endurance — better oxygen and nutrient delivery during exercise
- Reduced fatigue — enhanced ammonia clearance via the urea cycle
- Blood pressure support — modest reductions in systolic BP (3–5 mmHg)
- Erectile function — improved blood flow supports vascular health
Why citrulline and not arginine?
You might wonder: why not just take arginine directly? Because arginine taken orally is largely broken down by arginase in the liver before reaching systemic circulation. Citrulline bypasses the liver, is converted to arginine in the kidneys, and actually raises blood arginine levels more effectively than arginine supplements do.
How to take it
For performance: 6–8 g citrulline malate (or 3–5 g pure L-citrulline) taken 30–60 minutes before exercise.
For daily cardiovascular support: 3–6 g per day, split into 2 doses. Can be taken without regard to exercise timing.
Citrulline malate vs L-citrulline: Citrulline malate is citrulline bonded to malic acid (2:1 ratio). The malate may provide additional energy production benefits via the Krebs cycle. L-citrulline is pure citrulline without the malate. Both work; citrulline malate is more studied for exercise performance.
Side effects & safety
Citrulline has an excellent safety profile:
- Stomach discomfort — possible at doses above 10 g; take with water
- Mild headache — rare, from vasodilation; usually resolves as your body adapts
- No serious side effects — studied at doses up to 15 g/day without safety concerns
Who should be cautious: People on blood pressure medications (citrulline can lower BP further) and those on PDE5 inhibitors (sildenafil/Viagra) — both are vasodilators and combining them may cause excessive BP drops.
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Get early accessFrequently Asked Questions
Is citrulline better than arginine for nitric oxide?
Yes. Oral citrulline raises blood arginine (and thus NO production) more effectively than oral arginine. This is because arginine is heavily metabolised by arginase in the liver during first-pass metabolism, while citrulline bypasses this and is converted to arginine in the kidneys. Multiple studies confirm higher plasma arginine levels from citrulline supplementation vs arginine supplementation.
When should I take citrulline?
For exercise performance, take 6–8 g citrulline malate 30–60 minutes before training. For daily cardiovascular support, timing matters less — split into 2 doses throughout the day. Citrulline can be taken on an empty stomach or with food.
Does citrulline help with erectile dysfunction?
Citrulline can improve mild ED by enhancing nitric oxide production and blood flow. A small Italian study showed 1.5 g/day of L-citrulline improved erection hardness scores in men with mild ED. It's not as potent as PDE5 inhibitors (Viagra/Cialis) but can be a supportive natural option, especially alongside other cardiovascular health measures.
Is citrulline available in India?
Yes. L-citrulline and citrulline malate are available from AS-IT-IS Nutrition, MuscleBlaze, and international brands on Amazon India and iHerb. Prices range from ₹800–1,500 for 200 g powder. Most pre-workout supplements also contain citrulline, though often underdosed (look for at least 6 g citrulline malate per serving).
The nitric oxide pathway
Citrulline → arginine → nitric oxide (NO) is the core pathway. Nitric oxide synthase (NOS) converts arginine to NO and citrulline (yes, citrulline is also a byproduct of NO synthesis, creating a recycling loop). NO then diffuses into smooth muscle cells in blood vessel walls, activating guanylate cyclase, increasing cGMP, and causing vasodilation.
The arginine paradox: Despite arginine being the direct substrate for NO synthesis, plasma arginine levels are normally far above the Km of NOS — meaning NOS should always have enough arginine. Yet citrulline supplementation still increases NO production. This "arginine paradox" is partly explained by citrulline providing arginine specifically to the endothelial cells where NOS operates, bypassing hepatic metabolism.
Performance data: A meta-analysis of 12 RCTs found citrulline supplementation significantly improved high-intensity exercise performance, with the most consistent benefits at 6–8 g citrulline malate taken 40–60 minutes pre-exercise. Benefits include reduced perceived exertion, increased time to exhaustion, and improved power output in repeated sprint protocols.
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