NOW Foods Arginine 500 mg and Citrulline 250 mg Veg Capsules: Synergistic Nitric Oxide & Vascular Support
Unlock sustained blood flow, enhanced workout endurance, and healthy circulation with a research-driven 2:1 ratio of free-form L-Arginine and L-Citrulline.
Fast Summary: Why This Combination Works Better Than Arginine Alone
Taking standard L-Arginine by itself often falls short because your digestive tract and liver break down up to 50% of it before it reaches your bloodstream. By pairing 500 mg of pure L-Arginine with 250 mg of L-Citrulline, this formula creates a dual-action pathway: Arginine provides an immediate surge in circulating amino acids, while Citrulline easily passes through the liver to act as a steady, internal reservoir that recharges Arginine levels for hours.
The Science in Plain English: Understanding the "Arginine Paradox" and 2:1 Synergy
To understand why NOW Arginine 500mg and Citrulline 250mg is engineered this way, imagine a busy morning commute. Taking standard L-Arginine is like driving straight into a major highway toll booth with heavy traffic: your intestine and liver contain an active enzyme called arginase, which captures and breaks down a massive portion of the arginine before it can reach your arteries. Scientists refer to this biochemical hurdle as first-pass hepatic metabolism.
L-Citrulline acts like an express bypass lane. Your liver does not filter Citrulline out. Instead, Citrulline glides through the digestive system completely intact, journeys directly to the kidneys and blood vessel walls, and is systematically converted back into high concentrations of pure L-Arginine via two natural enzymes (argininosuccinate synthase and argininosuccinate lyase).
Supplement Route
Liver Breakdown (First-Pass)
Speed of Action
Circulating Blood Levels Duration
L-Arginine Alone
High (Up to 40%–50% lost)
Fast initial spike
Short half-life (drops quickly)
L-Citrulline Alone
None (Bypasses liver arginase)
Gradual onset
Long-lasting elevation
NOW Dual Combo (500mg/250mg)
Optimized dual-phase delivery
Immediate & Sustained
Prolonged plasma Arginine & Nitric Oxide
Clinical Reference Note: Peer-reviewed pharmacokinetics demonstrate that oral Citrulline supplementation raises systemic plasma L-Arginine concentrations more effectively than an equivalent dose of L-Arginine by itself (Schwedhelm et al., British Journal of Clinical Pharmacology, 2008).
Core Health & Athletic Benefits: Nitric Oxide, Vascularity, and Waste Removal
Your blood vessels are lined with a delicate cell layer called the endothelium. These cells synthesize Nitric Oxide (NO), a vital signaling gas that instructs vascular smooth muscle tissue to relax. When blood vessels relax, they gently widen (vasodilation), supporting healthy blood pressure ranges already within normal limits, promoting peripheral circulation, and reducing heart workload.
During heavy resistance training or rigorous cardio, working muscles demand substantial influxes of fresh oxygen, glucose, and essential amino acids. Heightened nitric oxide production facilitates microvascular blood delivery directly into working skeletal muscle fibers. This expanded blood volume creates the intense muscle fullness and vascularity athletes call "the pump," while delaying time to physical exhaustion.
Intense muscular exertion and high-protein nutrition produce metabolic waste, specifically toxic ammonia (NH3). Excess ammonia buildup triggers deep muscular fatigue and inhibits energy creation. Both Arginine and Citrulline serve as foundational intermediates in the hepatic urea cycle, where they rapidly convert toxic ammonia into harmless urea for safe renal elimination, speeding up post-workout recovery.
Verified Product Ingredients & Nutritional Facts
Formulation specifications verified directly against NOW Foods product standards (MFG Item # 0037, UPC 733739000378):
Supplement Facts
Serving Size: 1 Veg Capsule
Servings Per Container: 120
Amount Per Serving
% Daily Value
L-Arginine (Free-Form)
500 mg *
L-Citrulline (Free-Form)
250 mg *
* Daily Value (DV) not established.
Other Ingredients: Hypromellose (cellulose capsule), Stearic Acid (vegetable source), and Silicon Dioxide.
Allergen & Purity Profile: Not manufactured with wheat, gluten, soy, corn, milk, egg, fish, shellfish, tree nut, or sesame ingredients. Produced in a GMP facility that processes other ingredients containing these allergens.
Uncompromising Quality: NOW Foods In-House Testing & Strict Contaminant Limits
In an industry flooded with unregulated marketplace sellers, cut corners, and unverified imports, NOW Foods stands apart as one of the world's most trusted manufacturers. Headquartered in Bloomingdale, Illinois, NOW operates state-of-the-art analytical testing facilities designed to verify every single batch before it enters a bottle.
ISO/IEC 17025 Accredited Laboratories
NOW maintains in-house laboratories accredited to the ISO/IEC 17025 standard. Their team of over 150 quality control specialists—including more than 60 analytical chemists and microbiologists—performs over 19,000 comprehensive tests each month across raw ingredients and finished goods.
Trace Heavy Metal Screening (ICP-MS)
Using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), NOW screens raw ingredients for heavy metal contaminants down to parts-per-billion (ppb) detection limits. Every batch is rigorously verified against lead, mercury, cadmium, and arsenic thresholds, meeting or exceeding California Prop 65 and USP standards.
Potency Verification via HPLC / UPLC
Through High-Performance Liquid Chromatography (HPLC) and Ultra-Performance Liquid Chromatography (UPLC), raw amino acids are tested for molecular purity, identity, and potency, guaranteeing you receive the exact 500 mg Arginine and 250 mg Citrulline stated on the label with zero hidden fillers.
Microbiological & Chemical Screening
Every lot undergoes advanced pathogen testing for Salmonella, E. coli, yeasts, and molds, as well as GC-MS screenings for hundreds of agricultural pesticides and solvent residues. NOW has maintained an unbroken "A" rating from the NPA cGMP certification program since 2001.
How to Take for Maximum Results: Suggested Protocols & Timing
Consume between meals on an empty stomach with a full glass of water.
Maintains sustained plasma nitric oxide levels around the clock.
Protocol B: Pre-Workout Endurance & Muscle Pump
Take 2 capsules approximately 30 to 45 minutes prior to physical training.
Take with water or light carbohydrate juice (avoid high-fat or heavy protein foods).
Maximizes active blood flow, vasodilation, and muscle nutrient delivery during sets.
Absorption Tip: Amino acids absorb most efficiently when they do not compete with large dietary proteins. For ideal uptake, take these capsules at least 30 minutes before eating or two hours following a meal.
Important Safety, Drug Interactions & Medical Constraints
Because L-Arginine and L-Citrulline directly influence blood vessel diameter, blood pressure, and cellular biochemical pathways, this product is not appropriate for everyone. Always discuss dietary supplement additions with your personal physician, particularly if any of the following apply:
Blood Pressure Medications & Nitrates: Nitric oxide promotes blood vessel relaxation. Combining this formula with prescription antihypertensive drugs, prescription nitrates (such as nitroglycerin), or PDE-5 inhibitors (e.g., sildenafil, tadalafil) can cause additive vasodilation, potentially resulting in dangerous hypotension (low blood pressure).
Herpes Simplex Virus (Cold Sores / Genital Outbreaks): The Herpes Simplex virus (HSV-1 and HSV-2) requires L-arginine to replicate its genetic material. Individuals prone to cold sores or shingles may find that high arginine supplementation triggers viral reactivation. If taking arginine, many practitioners recommend balancing it with supplemental L-lysine, which competes against arginine uptake.
Prior Heart Attack (Myocardial Infarction): Large-scale clinical evaluations (including the VINTAGE MI trial) have cautioned that high-dose L-arginine supplementation is not advised for individuals with recent acute myocardial infarction or advanced coronary artery disease.
Kidney Disease or Glaucoma: People with kidney impairment or glaucoma should avoid supplemental arginine unless directly supervised and prescribed by their treating medical physician.
Disclaimer: For adults only. Do not consume if pregnant or nursing. Keep out of reach of children. Store in a cool, dry, dark environment after opening.
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In an era where unauthorized third-party online resellers warehouse degraded inventory in unconditioned garages, buying your health supplements from an established, authentic retailer is essential to ensure safety, potency, and freshness.
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VitaNet, LLC is a proudly independent, family-owned discount vitamin and herb retailer established in Hartville, Ohio[cite: 1]. With over 31 years of direct, hands-on experience in the dietary supplement industry, our team understands product purity and human biochemistry inside and out[cite: 1].
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We believe in risk-free wellness[cite: 1]. We offer a full 100% money-back guarantee on all products, and unlike most online outlets, we even pay the return shipping costs—even on opened bottles[cite: 1].
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Every bottle of NOW Arginine and Citrulline is ordered through direct manufacturer distribution channels, assuring authentic lot codes, fresh manufacturing dates, and strictly temperature-regulated storage.
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Our long-standing BBB A+ rating reflects three decades of honest, dependable customer service and transparent advice[cite: 1]. You can reach out to real product specialists right here in Ohio whenever you have a question[cite: 1].
Frequently Asked Questions (FAQ)
What is the purpose of combining L-Arginine and L-Citrulline together?
L-Arginine and L-Citrulline work synergistically. When taken alone, substantial amounts of oral L-arginine are broken down by intestinal and liver enzymes. L-Citrulline bypasses liver metabolism and converts to L-arginine in the kidneys. By taking both together, you receive an immediate increase in arginine from the free-form L-arginine, followed by a sustained, steady release as the L-citrulline converts over several hours, ensuring longer nitric oxide activity.
How does this formula support workout pumps and athletic performance?
These amino acids are the primary biochemical precursors for nitric oxide synthesis. Nitric oxide prompts the smooth muscle walls of your blood vessels to relax, widening arterial channels. During resistance training, this vasodilation pumps a greater volume of oxygen- and nutrient-rich blood directly into contracting muscle tissues, enhancing muscular fullness and accelerating metabolic waste removal.
When should I take NOW Arginine and Citrulline?
For athletic performance, take 2 capsules 30 to 45 minutes prior to working out on an empty stomach with a large glass of water. For general cardiovascular and circulation maintenance, take 1 capsule twice daily between meals or at bedtime.
Can I take this supplement if I get cold sores?
Caution is advised. The Herpes Simplex virus (which causes cold sores) utilizes L-arginine for viral replication. Individuals with a history of recurrent cold sores may experience outbreaks if blood arginine levels rise significantly without adequate L-lysine balance. If you are prone to outbreaks, consult your healthcare practitioner before use.
Does this product interact with prescription blood pressure medications?
Yes, potential interactions exist. Because both arginine and citrulline promote blood vessel relaxation and natural vasodilation, taking them alongside prescription blood pressure medications (antihypertensives), heart nitrates (such as nitroglycerin), or erectile dysfunction medications (PDE-5 inhibitors) may cause blood pressure to drop lower than intended. Always check with your prescribing doctor first.
How does NOW Foods ensure the purity and absence of heavy metals?
NOW Foods conducts over 19,000 lab analyses monthly in their in-house, ISO/IEC 17025 accredited analytical laboratories. They utilize Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to detect heavy metals (lead, arsenic, cadmium, mercury) down to parts-per-billion levels and verify amino acid purity using High-Performance Liquid Chromatography (HPLC).
Scientific References & Authoritative Sources
Schwedhelm, E., Maas, R., Freese, R., et al. (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. doi:10.1111/j.1365-2125.2007.02990.x
Allerton, T. D., Proctor, D. N., Stephens, J. M., et al. (2018). l-Citrulline Supplementation: Impact on Cardiometabolic Health. Nutrients, 10(7), 921. doi:10.3390/nu10070921
Gough, L. A., Sparks, S. A., McNaughton, L. R., et al. (2021). A critical review of citrulline malate supplementation and exercise performance. European Journal of Applied Physiology, 121(12), 3283–3295. doi:10.1007/s00421-021-04774-6
Curis, E., Nicolis, I., Moinard, C., et al. (2005). Almost all about citrulline in mammals. Amino Acids, 29(3), 177–205. doi:10.1007/s00726-005-0235-4
Kim, I. Y., Schutzler, S. E., Schrader, A., et al. (2015). Acute ingestion of citrulline stimulates nitric oxide synthesis but does not increase blood flow in healthy young and older adults. American Journal of Physiology-Endocrinology and Metabolism, 309(11), E915–E924. doi:10.1152/ajpendo.00339.2015
