Citrulline supplementation improves blood flow and increases the number of exercise repetitions performed under high-repetition, short-rest conditions, but does not lead to significant muscle hypertrophy over time.

Study: Oral L-citrulline supplementation enhances cycling time trial performance in healthy trained men: Double-blind randomized placebo-controlled 2-way crossover study

This study found that taking citrulline helped athletes cycle faster and feel less tired, which means it likely helps with endurance during tough workouts. But it didn't measure if muscles get bigger over time, so we don't know about that part.

Study: L-Citrulline Supplementation Improves Arterial Blood Flow and Muscle Oxygenation during Handgrip Exercise in Hypertensive Postmenopausal Women

This study found that taking citrulline helped women get more blood to their muscles during exercise, making it easier to work out longer. It didn't test whether it makes muscles bigger, so we don't know about that part.

Study: Changes in resistance training performance, rating of perceived exertion, and blood biomarkers after six weeks of supplementation with L-citrulline vs. L-citrulline DL-malate in resistance-trained men: a double-blind placebo-controlled trial

This study found that taking citrulline helped people do more reps during workouts, likely because it improves blood flow. But it didn’t measure if muscles got bigger over time, so we don’t know about that part.

Study: Nutritional Supplements for Muscle Hypertrophy: Mechanisms and Morphology—Focused Evidence

Citrulline helps you do more reps and recover faster during workouts, but it doesn’t make your muscles bigger over time—like a helper, not a muscle builder.