L-arginine and L-citrulline are two amino acids bundled into a single powerful supplement designed to help your body produce nitric oxide—the natural compound responsible for dilating blood vessels and keeping circulation smooth. While many single-ingredient supplements get broken down too quickly by the digestive tract, Source Naturals combines both nutrients in a proven 3:1 ratio (750 mg of L-Arginine to 250 mg of L-Citrulline per tablet). This gives your muscles the immediate boost they need while sustaining vascular blood flow and clean workout recovery for hours.
Why Athletes and Health-Conscious Adults Choose This Dual Complex:
✓Dual-Action Nitric Oxide Production: L-Arginine works immediately in the bloodstream, while L-Citrulline acts as a reserve engine to maintain sustained circulation.
✓Enhanced Muscle Metabolism: Supplies essential building blocks directly to exercising tissues for better pumps, muscular power, and stamina.
✓Post-Workout Ammonia Clearance: Accelerates the urea cycle to flush out cellular metabolic waste, cutting post-exercise soreness and fatigue.
✓High-Potency 240-Tablet Value: Provides a flexible 60-to-240-day supply depending on whether you take it for daily arterial support or intense fitness training.
The Science Made Simple: Why Combining L-Arginine and L-Citrulline Outperforms Single Amino Acids
To understand how this formula works, imagine your blood vessels are like garden hoses. When the inner lining of your blood vessels produces nitric oxide (NO), the muscular walls around those hoses relax. They open up wider, blood flows effortlessly, and oxygen and nutrients rush into your hard-working muscles and organs.
The "Arginine Trap" and How L-Citrulline Solves It
L-arginine is an important factor in muscle metabolism and a precursor for nitric oxide, which promotes increased circulation by relaxing blood vessels. However, when you take standard L-arginine on its own, a large portion of it is destroyed in your intestines and liver by an enzyme called arginase before it can ever reach your bloodstream. Scientists call this extensive "first-pass metabolism."
That is where L-citrulline steps in. Think of L-citrulline as an armored delivery vehicle:
1. Bypassing Liver Breakdown
L-citrulline completely slips past intestinal and liver enzymes without being destroyed. It travels cleanly to the kidneys, where it is transformed directly into fresh, pure L-arginine inside your body.
2. Blocking Arginine Destruction
L-citrulline naturally shuts down arginase enzymes. By slowing down the breakdown of L-arginine, it allows both nutrients to work in harmony, keeping blood nitric oxide levels higher for much longer.
Clinical Validation: In a double-blind crossover human trial published in Bioscience, Biotechnology, and Biochemistry (Suzuki et al., 2019), researchers found that taking oral L-citrulline and L-arginine in combination raised plasma arginine concentrations and blood nitric oxide metabolites far more efficiently than taking either amino acid alone, producing measurable improvements in high-intensity power output and stamina.
Key Physical Benefits: From Heavy Lifts to Everyday Circulation
During resistance training and aerobic exercise, working muscles demand an immediate surge of oxygen and fuel. By relaxing vascular smooth muscle tissue, this complex encourages healthy microcirculation. Athletes report fuller muscle pumps, better nutrient delivery to muscle fibers, and reduced physical fatigue during strenuous sets.
2. Ammonia Clearance: Your Body's Internal Cleanup Crew
L-citrulline helps the body rid itself of ammonia, a by-product of exercise. This clearing enables the body to recover after a workout. When you push your muscles hard, your body burns proteins and produces toxic ammonia, leading to that heavy, burning exhaustion. Citrulline acts as a key fuel for the urea cycle, safely converting ammonia into urea so your kidneys can flush it out, reducing post-workout muscle soreness.
3. Cardiovascular & Endothelial Health Support
Your endothelium is the delicate inner lining of your blood vessels. Nitric oxide keeps these vessel walls elastic, pliable, and responsive. Peer-reviewed clinical reviews show that maintaining healthy endothelial nitric oxide synthesis helps support healthy blood pressure already within a normal range and promotes full-body cardiovascular wellness.
Complete Supplement Facts & Ingredient Listing
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Supplement Facts
Serving Size: 1 Tablet • Servings Per Container: 240
Suggested Daily Serving: Up to 4 Tablets Daily (4,000 mg Complex)
Amount Per Serving
Per 1 Tablet
Per 4 Tablets (Daily)
% DV
Calories
5
20
<1%*
L-Arginine (as L-arginine hydrochloride)
750 mg
3,000 mg
†
L-Citrulline
250 mg
1,000 mg
†
* Percent Daily Values (% DV) are based on a 2,000 calorie diet.
† Daily Value not established.
Take 1 tablet four times daily with water, preferably between meals or approximately 30 to 45 minutes prior to physical exercise.
For Pre-Workout Performance: Take 2 tablets 45 minutes prior to training on an empty stomach to maximize nitric oxide surge, and 1 to 2 tablets later in the day.
For Daily Circulation & Recovery: Space 1 tablet evenly across the morning, midday, afternoon, and evening to ensure sustained blood amino acid levels.
Important Medical Precautions & Contraindications:
Your safety is paramount. Because nitric oxide amino acids naturally relax vascular smooth muscle, please observe the following clinical guidelines:
Not Recommended Following Heart Attacks: Do not use this product if you have experienced acute myocardial infarction (heart attack).
Prescription Medications: If you take prescription blood pressure medications, nitrates (such as nitroglycerin), or PDE-5 inhibitors for erectile dysfunction, speak with your doctor prior to use, as combining them may cause blood pressure to drop too low (hypotension).
Medical Conditions: Consult your healthcare provider if you have a history of heart disease, kidney (renal) disease, or liver (hepatic) failure.
Pregnancy & Nursing: If you are pregnant, may become pregnant, or are currently breastfeeding, consult your physician before use.
Storage & Tamper Protection: Do not use if either tamper-evident seal is broken or missing. Keep out of reach of children. Store in a cool, dry place.
Frequently Asked Questions (FAQ)
What is the main benefit of combining L-Arginine with L-Citrulline?
Combining them creates a powerful synergistic effect. L-arginine provides immediate nitric oxide production to relax blood vessels, while L-citrulline bypasses liver breakdown and converts into sustained L-arginine in the kidneys. This dual action keeps nitric oxide levels elevated for hours longer than taking either amino acid alone.
How does L-Citrulline help reduce workout soreness and fatigue?
During intense exercise, your muscles generate ammonia as a byproduct of energy metabolism, which contributes to fatigue and burning sensations. L-citrulline is a vital component of your body's urea cycle, helping flush ammonia out of your system quickly so your muscles recover faster after training.
When is the best time to take Source Naturals L-Arginine L-Citrulline Complex?
For athletic performance and muscle pumps, take 1 to 2 tablets roughly 30 to 45 minutes before working out on an empty stomach. For general cardiovascular and circulation support, take 1 tablet up to four times daily between meals spread throughout the day.
How long will one 240-tablet bottle last?
If you follow the full recommended daily use of 4 tablets daily (providing 3,000 mg of L-Arginine and 1,000 mg of L-Citrulline), one bottle delivers a full 60-day (2-month) supply. If you take 1 or 2 tablets daily for maintenance, one bottle can last between 120 and 240 days.
Does this product contain gluten, soy, dairy, or artificial additives?
No. Source Naturals L-Arginine and L-Citrulline Complex contains no yeast, dairy, egg, gluten, soy, or wheat. It is also completely free of sugar, starch, salt, preservatives, and artificial colors, flavors, or fragrances.
Can I take this supplement if I take blood pressure medication?
You should consult your prescribing physician before using this supplement if you take antihypertensive drugs, heart medications, nitrates, or medications for erectile dysfunction. Because L-arginine and L-citrulline promote natural blood vessel dilation, combining them with medications that also lower blood pressure requires medical supervision.
Scientific References & Clinical Studies
Suzuki, T., Morita, M., Kobayashi, Y., & Kamimura, A. (2019). Oral L-citrulline and L-arginine supplementation synergistically increases plasma L-arginine and nitric oxide production: A randomized, double-blind, placebo-controlled crossover study. Bioscience, Biotechnology, and Biochemistry, 83(6), 1147–1155. [PMID: 30845641]
Schwedhelm, E., Maas, R., Freese, R., Jung, D., Lukacs, Z., Jambrecina, A., Spickler, W., & Böger, 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. [PMID: 17662090]
Bendahan, D., Mattei, J. P., Ghattas, B., Confort-Gouny, S., Le Guern, M. E., & Cozzone, P. J. (2002). Citrulline/malate promotes aerobic energy production and post-exercise recovery in humans. British Journal of Sports Medicine, 36(4), 282–289. [PMID: 12145119]
Rhim, H. C., Kim, S. J., Park, J., & Jang, K. M. (2020). Effect of citrulline on post-exercise rating of perceived exertion, muscle soreness, and blood lactate levels: A systematic review and meta-analysis. Journal of Sports Science & Medicine, 19(3), 515–524. [PMID: 32874116]
Dong, J. Y., Qin, L. Q., Zhang, Z., Zhao, Y., Wang, J., Arigoni, F., & Zhang, W. (2011). Effect of oral L-arginine supplementation on blood pressure: a meta-analysis of randomized, double-blind, placebo-controlled trials. American Heart Journal, 162(6), 959–965. [PMID: 22137067]
Morita, M., Hayashi, T., Sumi, D., et al. (2014). Oral L-citrulline and L-arginine exerted synergistic effects on vascular endothelial function and plasma L-arginine levels in animals. Biochemical and Biophysical Research Communications, 454(2), 246–251. [PMID: 25444888]
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Always consult your personal physician before beginning any new nutritional supplement routine.
