L-citrulline (malate)

What it is

L-citrulline is a non-essential amino acid. Your body makes it itself, and the kidney converts it into arginine. In the diet it comes, among other sources, from watermelon.

Two forms are sold: pure L-citrulline and citrulline malate, a compound with malic acid. Most sports studies have used citrulline malate, often 8 g before training. Whether the malate form contributes anything was long an open question. A direct comparison in 33 strength-trained men over 6 weeks found no difference between 8 g of pure citrulline and 12 g of citrulline malate.

Citrulline is not purely a scene product. In France, citrulline malate has been approved as a medicine since 1991, for the supportive treatment of fatigue.

How it is supposed to work

Arginine is the direct raw material for nitric oxide, NO for short. NO relaxes the vascular muscles, and blood flows more easily. The problem: swallowed arginine is largely broken down in the gut and liver before it arrives.

Citrulline bypasses this bottleneck. It is well absorbed and only converted into arginine afterwards. A double-blind study with 20 volunteers showed that citrulline raises arginine levels dose-dependently more than arginine itself and increases NO-dependent signals. This part of the chain of action is established in humans.

The next step is less clear. More arginine in the blood does not automatically mean more blood flow in the muscle. At very high single doses, arginine also rose less than expected, probably because conversion in the kidney reaches a limit. Exactly how the higher arginine level turns into the training effect has not been fully measured in humans.

How citrulline is used in training

The studies on which the meta-analyses are based mostly give citrulline malate once, 40 to 60 minutes before training, usually 6 to 8 g. What is then mostly measured is how many repetitions you manage at a fixed weight until exhaustion.

Anyone hoping for a visible pump should adjust their expectations. In the only study that asked directly about the pump sensation, in 18 trained men and women, citrulline was not better than placebo.

Besides the single dose, there are studies with daily intake over several weeks. In the largest meta-analysis, the acute dose had a more consistent effect. In a 6-week study with 33 strength-trained men, however, L-citrulline taken daily improved upper-body strength endurance compared with placebo; for strength values and the lower body there was no significant difference.

What the studies show

Meta-analysis 2026: 30 studies, small effect

Wang and colleagues analyzed 30 randomized studies with 644 participants and 138 effect sizes, literature up to August 2025. Citrulline malate slightly improved overall exercise performance (g = 0.16, p = 0.01). Perceived exertion did not change significantly. The authors emphasize wide prediction intervals and rate the evidence as low to very low according to GRADE.

Meta-analysis 2021: repetitions in strength training

Vårvik and colleagues pooled 8 double-blind, placebo-controlled studies with 137 mostly trained participants. 6 to 8 g of citrulline malate 40 to 60 minutes beforehand produced on average 3 repetitions or 6.4% more to failure (p = 0.022). For the lower body the figure was 8.1% and narrowly missed significance; for the upper body it was 5.7% without significance.

Pharmacology 2008: citrulline beats arginine

In a double-blind crossover study, 20 healthy volunteers received 6 different dosing regimens of placebo, citrulline and arginine, each for one week. Citrulline raised arginine levels dose-dependently more than arginine itself and increased NO-dependent signals. This study is the basis for the statement that the detour via citrulline works better.

Meta-analysis 2020: muscle soreness and exertion

Rhim and colleagues analyzed 13 studies with 206 participants, mostly with 8 g of citrulline malate. Muscle soreness was lower 24 hours after training (p = 0.04); after 48 and 72 hours the difference was no longer significant. Perceived exertion fell; blood lactate did not.

Where the data stop

The performance effect is small and uncertain. The authors of the largest meta-analysis note that neither dose nor timing nor target group is established. On perceived exertion, two meta-analyses contradict each other. And the pump sensation, for which citrulline is most often bought, was not better than placebo in the only study that measured it. An immediate widening of the blood vessels could not be measured at 6 and 12 g in a study with 12 men either, even though arginine levels rose markedly.

On blood pressure, caution with numbers is warranted. A 2019 meta-analysis that had found minus 7.54 mmHg was retracted. The remaining analyses are inconsistent: one found minus 4.10 mmHg systolic, another no effect. On erections there is only one small, single-blind study with 24 men, in which half reported erections one grade harder with citrulline, compared with 8.3% with placebo. That is a signal, not proof. Studies beyond 17 weeks are missing.

Status, approval and legal

In Germany, citrulline is sold as a dietary supplement. For an arginine-citrulline product, the Federal Office of Consumer Protection and Food Safety issued a general ruling in 2013, with at most 65 mg of citrulline per day and warning notices. In France, citrulline malate has been approved as a medicine since 1991, 1 g per sachet. For competitive athletes, the general advice of the National Anti Doping Agency applies: dietary supplements can be contaminated, and the Cologne List lists independently tested products.

Safety

Citrulline is well tolerated. In a dose study with 8 men, single doses up to 15 g caused no side effects. In a training study with 41 men, 14.63% complained of stomach discomfort after 8 g of citrulline malate; the French summary of product characteristics lists occasional mild heartburn. Because citrulline intervenes in NO metabolism, the German general ruling provides for consulting a doctor if you take blood pressure medication or have kidney or liver disease. It also prescribes a warning notice for children, pregnant and breastfeeding women and people after a heart attack. There is no official upper limit, and the controlled studies ran for at most 17 weeks.

Sources

• Wang et al., Nutrients 2026 – meta-analysis, 30 RCTs, 644 participants
• Vårvik, Bjørnsen, Gonzalez, Int J Sport Nutr Exerc Metab 2021 – meta-analysis on repetitions
• Rhim et al., J Sport Health Sci 2020 – meta-analysis on muscle soreness and exertion
• Schwedhelm et al., Br J Clin Pharmacol 2008 – citrulline and arginine compared
• Moinard et al., Br J Nutr 2008 – dose finding up to 15 g
• Bayat et al., J Int Soc Sports Nutr 2025 – L-citrulline versus citrulline malate
• Gonzalez et al., J Funct Morphol Kinesiol 2023 – performance and pump sensation
• Barkhidarian et al., Avicenna J Phytomed 2019 – meta-analysis on blood pressure
• Retraction notice for Mahboobi et al., J Hum Hypertens 2021
• Cormio et al., Urology 2011 – citrulline in mild erectile dysfunction