What is citrulline? How it boosts nitric oxide and exercise performance

Citrulline is a non-essential amino acid that is converted to arginine through the urea cycle in the body and ultimately used for nitric oxide (NO) synthesis. NO dilates blood vessels, increasing blood flow, oxygen, and nutrient delivery to muscles. It is naturally found in watermelon flesh, but getting effective doses through supplementation is far more practical.

Non-essential amino acid

Produced in the body

Nitric oxide precursor

Triggers vasodilation

Oral arginine is largely broken down in the gut wall and liver before reaching the bloodstream (first-pass metabolism). Citrulline bypasses this degradation, so more of what you take actually makes it into circulation. Studies report that citrulline raises blood NO levels more efficiently than arginine itself — which is the main reason it has largely replaced arginine in pre-workout formulas.

Higher

Bioavailability vs. arginine

A 2010 RCT (Pérez-Guisado & Jakeman, JSCR) gave 41 trained men a single 8 g dose of citrulline malate 60 minutes before bench press to exhaustion. Compared with placebo, repetitions increased by an average of 52.92%, delayed-onset muscle soreness (DOMS) at 24–48 hours post-exercise fell by 40%, and perceived fatigue was significantly lower. Note that this was a single-dose, short-term study with a relatively small sample size — it is widely cited, but those limitations should be kept in mind.

+52.92%

Increase in bench press reps vs. placebo

−40%

Reduction in post-exercise DOMS score

8 g

Dose of citrulline malate used

Research predominantly uses 6–8 g of citrulline malate or 3–6 g of L-citrulline. Taking it 30–60 minutes before training is standard practice; the RCT above used a 60-minute pre-workout window. Because citrulline malate and L-citrulline have different conversion ratios, always check the form on the label — in a 2:1 citrulline malate product, a 6 g serving contains roughly 4 g of citrulline.

6–8 g

As citrulline malate

3–6 g

As L-citrulline

30–60 min before

Pre-workout timing

No serious side effects have been reported at typical doses (6–8 g). If you are taking antihypertensive medication, consult a doctor before use, as blood pressure may drop further. The information in this article is for educational and reference purposes only and does not constitute medical advice. Always consult a healthcare professional regarding dose and individual suitability.