What Is L-Citrulline and Why It Is in So Many Pre-Workouts
L-citrulline is a non-essential amino acid produced naturally in the body and found in watermelon. Its main role in sports nutrition is indirect: after ingestion, the kidneys convert it to L-arginine, which in turn serves as the substrate for nitric oxide (NO) synthase. The result is a sustained elevation in plasma arginine — and therefore NO — that supports vasodilation, blood flow, and the training pump. Unlike L-arginine taken directly, L-citrulline largely bypasses first-pass metabolism in the gut and liver, making it a more reliable way to raise circulating arginine (Schwedhelm et al., 2008).
Because of this well-established mechanism, L-citrulline has become a mainstay of quality pre-workout formulas and standalone supplements alike.
Two Main Forms: Free-Form vs Citrulline Malate
The two forms you will encounter most are:
L-Citrulline (free form): pure citrulline. Easier to dose precisely. Research on exercise performance and blood flow is often conducted with this form. MST L-citrulline 1100mg 120caps and MST L-Citrulline 240caps are examples of pure citrulline products with clearly labelled amounts.
Citrulline Malate (CM): citrulline bound to malic acid, typically in a 2:1 ratio by weight (two parts citrulline, one part malate). Because the malate portion contributes no citrulline, you need to account for this when comparing doses. A product labelled "Citrulline Malate 8 g" in a 2:1 ratio delivers around 5.3 g of actual citrulline. Research by Perez-Guisado and Jakeman (2010) found that citrulline malate was associated with reduced muscle soreness and improved exercise performance in trained subjects.
OstroVit Citrulline 4400 150caps and Olimp Citrulline Malate 200g Jahutav limonaad are examples available at maxfit.ee where the forms are clearly disclosed.
What to Look for on the Label
A quality l-citrulline product should display:
- Form specified: "L-Citrulline" or "Citrulline Malate (2:1)" — not just "citrulline"
- Milligrams per serving of citrulline (not just the total compound weight if malate is present)
- No proprietary blend that hides the citrulline amount
- Manufacturing standard such as GMP
If a product lists "citrulline" in a proprietary blend, you cannot know whether the dose is meaningful. Transparent labelling is the minimum standard a quality product should meet.
Third-Party Testing
Third-party testing is valuable for verifying that the declared amount of citrulline is actually present. Reputable programmes include Informed Sport and NSF Certified for Sport. Even without formal certification, a brand that publishes batch-level certificates of analysis from an independent laboratory demonstrates commitment to transparency.
For combination products (arginine plus citrulline, or pre-workout blends), third-party testing also checks that the blend does not contain undeclared stimulants or banned substances — particularly important for competitive athletes.
Red Flags
- No form specified or "citrulline blend" wording: vague labelling almost always means the amount is insufficient or the form is unspecified.
- Citrulline malate without stating the ratio: without the ratio, you cannot calculate the effective dose of citrulline.
- Very low price per serving for a high claimed dose: citrulline is a moderately expensive amino acid to produce. Suspiciously cheap products may be under-dosed.
- Claims of immediate vasodilation or guaranteed pump: physiological responses to NO-precursors vary between individuals. Any product promising specific sensory results is overstating what the science supports.
- No contact details or manufacturing address.
Dose Considerations
The research literature uses a range of doses for citrulline supplementation. Perez-Guisado and Jakeman (2010) used citrulline malate in their study on exercise performance. When dosing with pure L-citrulline rather than citrulline malate, you need a smaller absolute gram amount to deliver the same citrulline content. Calculating the effective dose is straightforward when a product declares its form and per-serving amount clearly — which is exactly why transparent labelling is so important.
Always calculate the citrulline content from the actual form listed. A product claiming a large serving weight may still be delivering a modest effective dose if it is a malate compound.
Value for Money
Pure L-citrulline powder is the most economical format per gram of effective citrulline. Products like NOW Foods Arginine 500mg & Citrulline 120caps offer a combination approach. Large powder formats usually deliver the best cost per gram of citrulline. Capsule formats are convenient for travel but typically cost more per gram. Flavoured powder formats sit in between.
Browsing the L-sitrulliin category at maxfit.ee lets you compare available formats and brands by declared amount and price per serving.
FAQ
Is citrulline malate better than pure L-citrulline?
Both forms supply citrulline to the body. Citrulline malate is more common in pre-workout research and may confer additional benefits from the malate component (which participates in the citric acid cycle). However, for delivering a given amount of citrulline, pure L-citrulline is more dose-efficient and generally costs less per gram of active ingredient.
When should I take L-citrulline?
Most pre-workout research uses doses taken approximately 60 minutes before exercise. This timing aligns with the time needed for intestinal absorption and conversion to arginine in the kidneys. Taking citrulline on an empty stomach is generally fine and may speed absorption.
Can I combine L-citrulline with other pre-workout ingredients?
Yes. Citrulline is commonly stacked with L-arginine, beta-alanine, and creatine without interaction concerns. The citrulline-arginine cycle is complementary, and combining them may help sustain plasma arginine levels (Schwedhelm et al., 2008). Avoid stacking with other NO-precursors beyond practical need — additional citrulline above a reasonable dose adds little further benefit per research evidence.
References
Schwedhelm, E., Maas, R., Freese, R., Jung, D., Lukacs, Z., Jambrecina, A., Spickler, W., Schulze, F., & Boger, R. H. (2008). Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism. British Journal of Clinical Pharmacology, 65(1), 51-59. https://pubmed.ncbi.nlm.nih.gov/17662090/
Perez-Guisado, J., & Jakeman, P. M. (2010). Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness. Journal of Strength and Conditioning Research, 24(5), 1215-1222.
Moinard, C., Nicolis, I., Neveux, N., Darquy, S., Benazeth, S., & Cynober, L. (2008). Dose-ranging effects of citrulline administration on plasma amino acids and hormonal patterns in healthy subjects: the Citrudose pharmacokinetic study. British Journal of Nutrition, 99(4), 855-862. https://pubmed.ncbi.nlm.nih.gov/17953788/
