L-Citrulline DL-Malate

What is L-citrulline?

L-citrulline is a non-essential amino acid named after watermelon (Citrullus), one of its richest food sources. Unlike most amino acids, it is not used to build proteins. Instead, the kidneys convert it into L-arginine, which blood vessels use to make nitric oxide. Supplements come as pure L-citrulline or citrulline malate, a combination with malic acid. Because malic acid adds weight, a given amount of citrulline malate supplies less citrulline than the same weight of pure L-citrulline.

What the research says

Raising arginine and nitric oxide markers

In a randomized crossover study in healthy volunteers, oral L-citrulline raised blood arginine levels in a dose-dependent way and more effectively than L-arginine. The highest dose, 3 grams twice a day, improved the ratio of arginine to its natural inhibitor ADMA and increased urinary nitrate and cGMP, markers of nitric oxide signaling. Blood vessel dilation did not improve on average, though changes tracked with the arginine/ADMA ratio (Schwedhelm et al., 2008).

Erectile function

In a single-blind study, 24 men with mild erectile dysfunction took placebo for a month and then 1.5 grams of L-citrulline a day for a month. While taking citrulline, 50% of men improved from mild dysfunction to normal hardness scores, compared with 8.3% during placebo, and no adverse events were reported (Cormio et al., 2011). The study was small, short and not fully blinded, and the effect was smaller than with prescription drugs. A later trial combined citrulline with trans-resveratrol in men already using a PDE5 inhibitor, making it hard to judge citrulline alone.

Exercise

Citrulline malate is popular as a pre-workout ingredient. The authors of one randomized trial described the evidence for exercise performance as equivocal, and in their own study eight days of 8 grams of citrulline or arginine did not improve swimming time trials or blood nitric oxide markers in trained swimmers (Esen et al., 2022).

How it’s used in supplements

Citrulline is sold as powder or capsules and appears in pre-workout mixes and men’s health blends. Studied doses for blood flow range from about 1.5 to 6 grams of L-citrulline a day, so check whether a label lists pure citrulline or citrulline malate. It is generally well tolerated, with occasional stomach upset. Because it raises nitric oxide signaling, it could add to the blood-pressure-lowering effects of nitrates, PDE5 inhibitors and blood pressure medicines. People with heart disease, low blood pressure or kidney disease, and those who are pregnant or breastfeeding, should talk to a doctor before use.