Taking citrulline supplements may help improve blood flow and allow more repetitions during high-repetition, short-rest workouts, but it does not cause measurable increases in muscle size over time.
Evidence from Studies
Supporting (4)
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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.
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.
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.
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.
Contradicting (1)
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Effects of Citrulline Malate and Beetroot Juice Supplementation on Blood Flow, Energy Metabolism, and Performance During Maximum Effort Leg Extension Exercise.
This study gave people a citrulline supplement mixed with another compound and found it didn’t help them lift more reps or improve blood flow during workouts. So it doesn’t support the idea that citrulline boosts performance.
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.