L-Citrulline
SupplementThe divergence arises from clinical-scientific limitations due to small study sample sizes and heterogeneous dosing [s3, s5], while users in practice consistently report pronounced pump and endurance effects [c1, c2, c3].
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TL;DR
L-citrulline is one of the better-evidenced pre-workout supplements: it raises NO bioavailability more effectively than L-arginine (bypassing intestinal arginase first-pass metabolism), demonstrably reduces muscle soreness and RPE, and produces a moderate blood pressure reduction. The effective dose is at least 6 g of pure L-citrulline — with citrulline malate 2:1, 8 g of product yields only ~5.3 g of active compound. Combining with PDE5 inhibitors is contraindicated due to additive hypotensive effects.
Description
Non-essential amino acid converted in the body to L-arginine and nitric oxide; well-evidenced for muscle pump, endurance performance, and moderate blood pressure reduction [s1, s3, s5].
L-Citrulline is a non-essential amino acid naturally occurring in watermelon that plays a central role in the urea cycle. Compared to L-arginine, L-citrulline has significantly higher oral bioavailability, as it bypasses intestinal arginase activity and is thus converted more efficiently to plasma L-arginine [s1]. L-Arginine in turn serves as a direct substrate for nitric oxide synthase (NOS), thereby increasing nitric oxide (NO) production [s1, s2]. In sports nutrition, L-citrulline is commonly used as a "pump" supplement, as NO-mediated vasodilation improves blood flow to working musculature [s3]. Clinical studies demonstrate benefits in reducing perceived exertion (RPE), delayed onset muscle soreness (DOMS), and blood lactate following intense exercise [s3, s4]. A meta-analysis (2019, n=8 studies) confirmed significant blood pressure reduction through L-citrulline supplementation [s5]. Small RCTs with positive findings exist for mild-to-moderate erectile dysfunction [s6, s7]. L-Citrulline is marketed both as a free amino acid and as citrulline malate (2:1 ratio with malic acid). The superiority of either form has not been conclusively established scientifically; with citrulline malate, the effective citrulline dose is lower due to the malate fraction [s4, s8]. No relevant adverse effects have been reported at doses up to 15 g/day [s9].
Legal Status (DE)
L-Citrulline is freely marketable in Germany as a food supplement (NEM). The BVL has issued a general administrative act for food supplements containing L-arginine and L-citrulline (BVL 13/01/018). No binding maximum levels for amino acids in food supplements exist at the national or European level. EFSA health claims for L-citrulline have not been authorized [s11, s12].
Mechanism of Action
Following oral ingestion, L-citrulline is absorbed primarily in the small intestine. Unlike L-arginine, it is not degraded by intestinal arginase, resulting in high bioavailability [s1]. In the kidneys, L-citrulline is converted by the enzyme argininosuccinate synthetase, together with aspartate, to argininosuccinate, which is then cleaved to L-arginine by argininosuccinate lyase [s1, s2]. The L-arginine thus obtained serves as a substrate for endothelial nitric oxide synthase (eNOS), which produces NO from L-arginine and oxygen [s2]. NO activates soluble guanylyl cyclase in vascular smooth muscle cells, raises cGMP levels, and thereby induces vasodilation [s2]. This mechanism accounts for the blood pressure-lowering effect and improved muscle blood flow during physical exertion [s5]. Additionally, L-citrulline can inhibit arginase activity, which normally competes with NOS for the shared substrate L-arginine, further promoting NO production [s2]. In the context of erectile function, citrulline inhibits phosphodiesterase 5 (PDE5) in a non-competitive manner, prolonging cGMP accumulation in the corpus cavernosum [s7]. Citrulline is also an intermediate of the urea cycle and may support ammonia detoxification during intense physical exercise [s3].
Dosing
Sportliche Leistung / Pump (Krafttraining)
- Dose
- 6–8 g L-citrulline (or 8–10 g citrulline malate 2:1)
- Frequency
- 1× täglich vor dem Training
- Route
- oral
- Duration
- fortlaufend
- Timing
- 30–60 minutes before training
- With food
- optional
Blutdrucksenkung / kardiovaskuläre Gesundheit
- Dose
- 3–6 g L-citrulline daily
- Frequency
- 1–2× täglich
- Route
- oral
- Duration
- 4–8 Wochen
- Timing
- Evenly distributed throughout the day
- With food
- optional
Erektile Dysfunktion (leicht bis moderat)
- Dose
- 1.5–3 g L-citrulline daily
- Frequency
- 1× täglich oder 1–2 Stunden vor der Aktivität
- Route
- oral
- Duration
- 2–4 Wochen (Dauereinnahme oder bedarfsorientiert)
- Timing
- Morning or 1–2 hours before anticipated need
- With food
- optional
Doses up to 15 g/day have been used in clinical studies without relevant adverse effects [s9]. For athletic purposes, a sustained dose exceeding 10 g/day is not supported by evidence of superior efficacy. No general maximum daily amount is established by regulation in Germany [s11, s12].
When using citrulline malate 2:1, 8 g of product contains only approximately 5.3 g of pure L-citrulline [s8]. For purely citrulline-based dosing, the free form is more efficient. The minimum effective dose is approximately 3 g/day [s4].
Side Effects
| Side Effect | Frequency | Severity |
|---|---|---|
| Gastrointestinale Beschwerden (Magenunwohlsein, weicher Stuhl) Compared to L-arginine and ornithine, gastrointestinal side effects with L-citrulline are significantly less frequent even at doses up to 15 g/day [s9]. | selten | leicht |
| Kopfschmerzen / Migräne (bei Überdosierung) Individual user reports on Reddit forums describe headaches at excessive doses, presumably due to pronounced vasodilation [c1]. | selten | leicht |
| Übermäßige Blutdrucksenkung (Hypotonie) Since L-citrulline increases NO production and induces vasodilation, hypotension is theoretically possible in individuals with low baseline blood pressure or concurrent use of antihypertensives [s5]. | theoretisch | moderat |
Contraindications
L-citrulline upregulates the NO/cGMP axis and inhibits PDE5; combination with PDE5 inhibitors may cause severe hypotension and cardiovascular events [s7].
The vasodilatory effect of L-citrulline via NO synthesis may further reduce an already low blood pressure [s5].
Additive blood pressure-lowering effect possible via NO elevation; medical consultation recommended [s5].
L-citrulline is primarily converted to L-arginine in the kidney; metabolic capacity is reduced in impaired renal function. Long-term data are lacking [s9].
Interactions
Synergistic
The combination of L-citrulline and L-arginine showed superior blood pressure reduction (systolic –10.44 mmHg, diastolic –4.86 mmHg) compared to individual substances in a meta-analysis [s10].
Frequently combined in strength sports; L-citrulline supports blood flow and creatine distribution in muscle tissue (mechanistically plausible, no direct RCT) [c1, c2].
L-citrulline and beta-alanine complement each other effectively in the pre-workout context. Citrulline improves blood flow via NO production, while beta-alanine increases intramuscular carnosine levels and delays fatigue by buffering lactic acid. The combination may synergistically enhance training performance.
L-citrulline can weakly stimulate mTORC1-dependent muscle protein synthesis, thereby acting complementarily to BCAAs/EAAs, which serve as direct substrates for protein synthesis. Studies in trained cyclists demonstrate combined use with potentially additive effects on performance.
Caution
Synergistic inhibition of cGMP degradation; combination may lead to severe hypotension and cardiovascular events. Contraindicated [s7].
Additive blood pressure-lowering effect; concurrent use requires medical monitoring of blood pressure [s5].
Both increase NO bioavailability; additive hypotension risk theoretically plausible (mechanistic) [s2].
Both substances can lower blood pressure — CoQ10 by improving mitochondrial and endothelial function, L-citrulline via increased NO production. Concurrent use may produce an additive blood pressure-lowering effect, which can cause dizziness or hypotension in susceptible individuals.
Both substances influence the nitric oxide system and promote angiogenesis. Concurrent use could theoretically lead to excessive neovascularization or undesirable vascular dysregulation. No clinical studies on this combination are available.
Studies
Tier A — High Evidence
Outcome: Systolic and diastolic blood pressure
Effect Size: Significant reduction in systolic blood pressure; moderate effect size; strongest effect in hypertensive subjects
Outcome: Resistance training performance, RPE, biomarkers in resistance-trained individuals
Effect Size: L-Citrulline and L-Citrulline-DL-Malate comparable; minimum effective dose approx. 3 g/day
Outcome: RPE, muscle soreness (DOMS), and blood lactate following exercise
Effect Size: Significant reduction in RPE and DOMS; blood lactate slightly reduced; moderate heterogeneity across studies
Outcome: Erection Hardness Score (EHS), coital satisfaction
Effect Size: EHS improvement from grade 2 to grade 3 in 50% of subjects under citrulline vs. 8.3% under placebo (p<0.01)
Tier B — Moderate Evidence
Outcome: IIEF score in men on PDE5 inhibitor therapy
Effect Size: Significant IIEF improvement with L-citrulline + transresveratrol vs. placebo
Outcome: Blood pressure reduction by L-citrulline + L-arginine combination
Effect Size: Systolic –10.44 mmHg, diastolic –4.86 mmHg
Outcome: Plasma concentration profiles of L-Citrulline, L-Arginine, and NO metabolites
Effect Size: L-Citrulline increases plasma arginine more effectively than oral L-Arginine
Tier C — Low Evidence
Outcome: Arginase inhibition and NOS competition by L-citrulline
Effect Size: Mechanistic description without direct effect size
Community Evidence
Top reported benefits
- Significantly enhanced muscle pump during resistance training
- Improvement of endurance performance and reduction of fatigue
- Improved vascularity (vein definition)
- Preference over L-Arginine due to better tolerability
- Positive experiences as a standalone pre-workout supplement
Top reported issues
- No perceptible effect when below the minimum effective dose (under 6 g)
- Occasional headaches at very high single doses
- Unclear added value of citrulline malate over pure L-citrulline
Some users report that commercially available pre-workout products frequently underdose L-citrulline (below 3 g), resulting in absent effects. No community consensus on the optimal ratio of citrulline malate to free L-citrulline.
Scientific Sources
- Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism
Schwedhelm E, Maas R, Freese R, et al. (2008). British Journal of Clinical PharmacologyBPMID:17922905DOI - The Effect of L-Citrulline Supplementation on Blood Pressure: An Updated Systematic Review and Meta-Analysis of Randomized Controlled Trials
Barkhidarian B, Roldos L, Iskandar MM, et al. (2024). Nutrients (ResearchGate preprint/publication)ALink - BVL Allgemeinverfügung BVL 13/01/018: Nahrungsergänzungsmittel mit Zusatz von L-Arginin und L-Citrullin
Bundesamt für Verbraucherschutz und Lebensmittelsicherheit (BVL) (2013). BVL Bundesrepublik DeutschlandALink - Fragen und Antworten zu Nahrungsergänzungsmitteln
Bundesinstitut für Risikobewertung (BfR) (2023). BfR, Bundesrepublik DeutschlandALink - Frontiers | L-Citrulline Supplementation Increases Plasma Nitric Oxide Levels and Reduces Arginase Activity in Patients With Type 2 Diabetes
Sanchez-Gonzalez MA, Kavazis AN, Sharpe W, et al. (2020). Frontiers in PharmacologyAPMID:33390945DOI - Effect of citrulline on post-exercise rating of perceived exertion, muscle soreness, and blood lactate levels: A systematic review and meta-analysis
Rhim HC, Kim SJ, Park J, et al. (2020). Journal of Sport and Health ScienceAPMID:33308806DOI - Changes in resistance training performance, rating of perceived exertion, and blood biomarkers after six weeks of supplementation with L-citrulline vs. L-citrulline DL-malate in resistance-trained men: a double-blind placebo-controlled trial
Gonzalez AM, Trexler ET, Townsend JR, et al. (2025). Journal of the International Society of Sports NutritionADOI - Effects of L-citrulline supplementation on blood pressure: A systematic review and meta-analysis
Khalaf D, Krüger M, Wehland M, et al. (2019). NutrientsAPMID:30736465DOI - Oral L-citrulline supplementation improves erection hardness in men with mild erectile dysfunction
Cormio L, De Siati M, Lorusso F, et al. (2011). UrologyAPMID:21195829DOI - Oral L-citrulline and Transresveratrol Supplementation Improves Erectile Function in Men With Phosphodiesterase 5 Inhibitors: A Randomized, Double-Blind, Placebo-Controlled Crossover Pilot Study
Shirai M, Hiramatsu I, Aoki Y, et al. (2018). UrologyAPMID:30150102DOI - Citrulline Malate vs L-Citrulline: Formulator's analysis of potency and performance
Nutripartners Editorial Team (2023). Nutripartners BlogCLink - Citrulline in health and disease. Review on human studies
Bahri S, Zerrouk N, Aussel C, et al. (2013). Clinical NutritionBPMID:23680657DOI
Community Sources
Storage
Unopened
Store cool, dry, and at room temperature; avoid direct sunlight.
Opened
Keep container tightly closed; moisture must be strictly avoided with powder, as it is hygroscopic.
Notes
Citrulline malate powder is slightly less hygroscopic than free L-citrulline. With correct storage, shelf life is guaranteed until the best-before date.