If you've cut back on caffeine or synthetic stimulants and you're looking for another way to support energy, L-Citrulline shows up constantly in that conversation. It's a plant-derived amino acid, found naturally in watermelon, that your body converts to L-Arginine, the direct building block your endothelium uses to produce nitric oxide. But does the actual research back up the energy claims? Here's a straight look.
The Mechanism: Why Citrulline Is Different From Stimulants
Synthetic stimulants create a feeling of energy by triggering your nervous system, which is why they come with a crash once that signal fades. L-Citrulline works through a completely different pathway: by supporting nitric oxide production, it may improve blood flow and oxygen delivery to working muscles. In theory, that means less reliance on anaerobic energy systems, the ones responsible for the burning, fatigued feeling during exertion, and a more efficient use of oxidative metabolism instead.
What the Research Actually Found
The evidence here is genuinely mixed, and it's worth saying that plainly rather than cherry-picking the studies that support the story. A double-blind, randomized, placebo-controlled crossover study published in the Journal of the International Society of Sports Nutrition found that L-Citrulline supplementation reduced the time needed to complete a cycling time trial, and improved participants' subjective sense of muscle fatigue and concentration immediately after exercise.
A separate study in the Journal of Applied Physiology found L-Citrulline improved oxygen uptake kinetics and high-intensity exercise performance, with researchers proposing that citrulline increases the proportional energy contribution from oxidative metabolism, potentially reducing the buildup of fatigue-related metabolites.
Other research complicates the picture. A study on resistance-trained men and women found a single 8-gram dose of L-Citrulline did not meaningfully improve force production, muscular endurance, or muscle oxygenation. A 2025 crossover trial described the existing literature on L-Citrulline and endurance performance as contradictory, noting that differences in testing protocols, dosing, and timing likely explain why some studies find a benefit and others don't.
The Honest Takeaway
L-Citrulline is not a stimulant, and it will not produce the immediate jolt (or the crash) associated with caffeine or synthetic pre-workout ingredients. What the research does support is a plausible, mechanistically sound role in supporting blood flow and oxygen delivery during physical exertion, with real but inconsistent evidence for reduced perceived fatigue. It's a reasonable, non-stimulant option to explore, not a guaranteed energy switch.
NEONOX includes L-Citrulline as part of its fully disclosed 5,100 mg Nitric Oxide Blend, alongside Beet Root Juice Powder and Pine Bark Extract, with zero synthetic stimulants and no proprietary blend hiding the actual dose.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.