6–8 g of citrulline malate before training; 3 g of L-citrulline for the vessels. There is no established supplementation protocol for IBD.
Increases repetitions and reduces muscle soreness.
View the study (clinical trial) →Plasma citrulline reflects enterocyte mass: it is low in Crohn's disease with an active inflammatory flare, in villous atrophy (celiac disease without a gluten-free diet), and in short bowel syndrome. Thresholds for intestinal failure: <10 μmol/L in villous atrophy, <20 μmol/L in short bowel. Useful for monitoring, not for diagnosis.
See the study (cohort studies) →Improves erection in mild cases.
View the study (clinical trial) →Plasma citrulline falls with inflammatory activity of Crohn's disease in children; it correlates with classic markers of flare and with the extent of the disease.
See the study (pediatric cohort) →There are NO randomized clinical trials showing that taking L-citrulline reduces Crohn's or ulcerative colitis activity. Its demonstrated role is as a marker of damage, not as a treatment. Extrapolating from the biomarker to a therapeutic effect is a leap not supported by data.
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L-citrulline is a non-proteinogenic amino acid found naturally in watermelon (in fact, it was first isolated from that fruit, hence its name, which comes from the Latin citrullus) and, to a lesser extent, in cucumbers and melons; its most relevant biological function is to be the precursor of L-arginine, the direct substrate for the enzyme nitric oxide synthase, which produces the nitric oxide responsible for arterial vasodilation and for much of the regulation of vascular tone throughout the body.
The choice of citrulline instead of taking L-arginine directly has an important pharmacokinetic reason: oral L-arginine undergoes extensive intestinal and hepatic metabolism (first-pass hepatic metabolism eliminates more than 50 percent), whereas L-citrulline passes through the intestine and liver intact, reaches the kidneys where it is efficiently converted into L-arginine, and raises plasma arginine levels in a more sustained and predictable way than direct arginine administration.
The indication with the best evidence is performance in endurance efforts and in high-repetition strength exercises: several randomized trials have shown that doses of 6 to 8 grams of citrulline malate taken one hour before exercise improve the number of repetitions performed before muscle failure, reduce post-exercise muscle soreness, and subjectively improve the sensation of fatigue during long sets.
The most plausible mechanism combines better vasodilation and better blood flow to the active muscle (more oxygen and nutrients available, better clearance of metabolites) with an effect on ammonia metabolism that delays the accumulation of this by-product, which inhibits muscle contraction; the effect is modest but replicable, and sufficient for many strength-endurance athletes to use it as a pre-workout tool.
In people with mild endothelial dysfunction, incipient hypertension, or cardiovascular risk factors, supplementation with 3 to 6 grams daily of L-citrulline for 4 to 12 weeks improves flow-mediated dilation (a functional marker of the endothelium) and modestly reduces systolic blood pressure by 4 to 8 mmHg, an effect comparable to that of some standard dietary interventions such as increasing nitrate-rich leafy vegetables.
In heart failure and peripheral arterial disease, several studies have shown functional improvements with prolonged supplementation, in a line of research that remains active but has not yet been consolidated in mainstream clinical guidelines; the cardiovascular effect of nitric oxide is well known, and citrulline offers safe and predictable access to that pathway without the adverse effects of more potent vasodilator drugs.
A specific and well-studied indication is mild to moderate erectile dysfunction of vascular origin: citrulline improves erectile function through the same mechanism as sildenafil-type drugs (the nitric oxide-cGMP pathway), although with quantitatively smaller effects, which makes it a reasonable first-line alternative in men with mild problems or an adjunct in men who prefer to avoid pharmacological medication.
The doses studied for this indication are 1.5 grams daily (of pure citrulline, not malate) for one month, with significant improvements on the IIEF scale and in participants' sexual satisfaction; the effect is smaller than that of sildenafil but the safety profile is excellent and it requires no advance planning, which some men prefer.
Effective doses range from 1.5 to 8 grams daily depending on the indication: 1.5–3 g/day for vascular and erectile function, 6–8 g/day (preferably as citrulline malate) taken 60–90 minutes before exercise for physical performance; it can be taken fasting or with food, with no significant difference in absorption; effects appear within minutes for acute vasodilation and within weeks to months for structural improvements of the endothelium.
It is one of the amino acids with the best safety profile: practically no adverse effects at the doses studied over months, with no relevant documented drug interactions; people who take pharmacological nitrates (nitroglycerin, isosorbide mononitrate) should be cautious because of the theoretical risk of vasodilator potentiation, and those who take phosphodiesterase 5 inhibitors (sildenafil, tadalafil) may experience a greater drop in blood pressure when combining both.
Information, not medical advice. Scientific evidence reflects the quality of the studies.