Endurlac
Also known as: Endurlac, Citrulline, (2S)-2-amino-5-(carbamoylamino)pentanoic acid, L-citrulline
Overview
L-citrulline, marketed as Endurlac, is a non-essential amino acid naturally found in watermelons and produced endogenously in the urea cycle. As a supplement, it is primarily utilized as an ergogenic aid to enhance exercise performance, endurance, and recovery. Its mechanism involves increasing nitric oxide (NO) production and facilitating ammonia clearance, leading to improved blood flow, reduced fatigue, and enhanced aerobic and anaerobic exercise capacity. Research on L-citrulline is moderately mature, with multiple randomized controlled trials (RCTs) and meta-analyses supporting its benefits, though some findings exhibit inconsistency due to heterogeneity in study designs. It is generally recognized for its ability to improve endothelial function and nutrient delivery to muscles.
Benefits
L-citrulline offers several evidence-based benefits, primarily in exercise performance. A 2023 systematic review and meta-analysis indicated that acute L-citrulline ingestion may improve endurance performance, specifically time-to-exhaustion or time-to-completion, in young healthy adults, though results are mixed and require further confirmation. Another 2022 meta-analysis reported positive effects on aerobic exercise performance, suggesting improved oxygen utilization and reduced fatigue. These studies often show small to moderate effect sizes (e.g., SMD ~0.3-0.5), indicating modest but potentially meaningful improvements. Secondary benefits include potential improvements in ammonia buffering and nitric oxide-mediated vasodilation, which can aid muscle recovery and reduce soreness. While young healthy adults and recreationally active individuals show some benefit, effects in elite athletes can vary. The benefits are typically observed with acute ingestion before exercise, though some protocols involve loading phases over several days.
How it works
L-citrulline's primary mechanism of action involves its conversion to L-arginine in the kidneys. L-arginine then serves as a substrate for nitric oxide synthase (NOS) enzymes, leading to the production of nitric oxide (NO). NO is a potent vasodilator, which enhances blood flow by relaxing blood vessels. This improved blood flow facilitates greater oxygen and nutrient delivery to working muscles during exercise, thereby enhancing performance and reducing fatigue. Additionally, L-citrulline plays a role in the urea cycle, aiding in the clearance of ammonia, a metabolic byproduct that can contribute to fatigue during intense physical activity. Its superior oral bioavailability compared to L-arginine allows for more effective elevation of plasma arginine levels.
Side effects
L-citrulline is generally considered safe for healthy adults when taken within recommended dosages, with a low incidence of adverse effects. The most commonly reported side effect, though still mild and infrequent, is gastrointestinal discomfort. No consistently reported uncommon or rare side effects have been documented in high-quality clinical trials. There are no major reported drug interactions, but caution is advised for individuals taking medications that affect blood pressure or nitric oxide pathways, such as vasodilators, due to the potential for additive effects. Individuals with pre-existing hypotension should also exercise caution. Safety data for pregnant or lactating women and children are limited, and its use in these populations is not well established. Overall, L-citrulline has a favorable safety profile, but users should be aware of potential mild GI issues.
Dosage
For ergogenic effects, studies commonly use L-citrulline doses ranging from 3 to 6 grams for acute benefits, with optimal daily dosages typically falling between 6 and 8 grams. Some research has explored doses up to 10 grams daily without significant adverse effects, suggesting this as a potential upper limit for safety. For acute performance enhancement, L-citrulline is usually taken 30-60 minutes before exercise. Loading protocols, where the supplement is taken over several days, are also employed in some research settings. Both L-citrulline and citrulline malate forms are used, with citrulline malate potentially offering additional benefits from the malic acid component. L-citrulline is well absorbed orally, and while no specific cofactors are required, overall nutritional status may influence its efficacy. Co-ingestion with carbohydrates might enhance its uptake.
FAQs
Is Endurlac safe?
Yes, within recommended doses, L-citrulline (Endurlac) is generally safe for healthy adults with minimal side effects, primarily mild gastrointestinal discomfort.
When should I take it?
For performance benefits, it is typically recommended to take L-citrulline 30-60 minutes before exercise to allow for optimal absorption and effect.
How soon will I see results?
Acute effects on performance can be observed within approximately one hour of ingestion. The effects of chronic supplementation are less clearly defined.
Does it work for everyone?
Individual responses to L-citrulline can vary. While many individuals, especially recreationally active ones, may experience benefits, the extent depends on factors like fitness level and exercise type.
Is it better than arginine?
Yes, L-citrulline generally has better oral bioavailability than L-arginine, meaning it is more effectively absorbed and converted to L-arginine in the body, leading to higher and more sustained plasma arginine levels.
Research Sources
- https://pubmed.ncbi.nlm.nih.gov/37155582/ – This 2023 systematic review and meta-analysis investigated the effects of acute citrulline ingestion on endurance performance in young healthy adults. It found potential ergogenic effects on time-to-exhaustion or time-to-completion, but noted inconsistencies across studies, suggesting more research is needed for conclusive evidence. The study was of high quality, adhering to PRISMA guidelines.
- https://pubmed.ncbi.nlm.nih.gov/36079738/ – This 2022 systematic review and meta-analysis examined the impact of citrulline supplementation on aerobic exercise performance. It reported positive effects, indicating improvements in oxygen utilization and reduced fatigue, despite some variability in dosing and exercise modalities across the included studies. The research was published in a peer-reviewed nutrition journal and considered high quality.
- https://www.nature.com/articles/s41598-024-84359-3 – This 2025 systematic review and Bayesian network meta-analysis analyzed 67 RCTs involving elite combat sports athletes to assess various supplements. While L-citrulline showed some benefit compared to placebo in combat sports performance, its effects were less pronounced than those of caffeine and sodium bicarbonate. The study was comprehensive and included bias assessment.
