NOW Arginine and Citrulline 500 / 250 mg (240 Veg Capsules)
Dual-Action Nitric Oxide Precursors for Healthy Blood Flow, Vascular Tone, and Muscle Recovery
Quick Takeaway: Taking L-arginine by itself is often inefficient because the liver breaks down most of it before it reaches your bloodstream. NOW Arginine and Citrulline 500 / 250 pairs 500 mg of pure L-arginine with 250 mg of pure L-citrulline. Citrulline glides through the digestive tract and turns back into arginine in your kidneys, giving you steady, extended nitric oxide production that promotes open blood vessels, better physical stamina, and healthy cardiovascular pressure.
Product Specifications at a Glance
Item SKUNOW N0038
Bottle Count240 Vegetarian Capsules
Active Ratio2:1 Synergistic Balance
Form100% Free-Form Amino Acids
The 2:1 Synergy: Why Arginine Alone Is Not Enough
Many people buy standalone L-arginine supplements hoping for better muscle pumps, cardiovascular endurance, and improved circulation. However, plain oral arginine has a well-known biological obstacle: first-pass hepatic metabolism.
1. The Arginase Bottleneck in Plain English
When you swallow L-arginine alone, intestinal bacteria and liver enzymes called arginase intercept and destroy an estimated 40% to 60% of it before it ever enters your systemic circulation (Castillo et al., 1993). As a result, you have to take very high doses to see benefits, which often leads to stomach cramps and loose stools.
2. How L-Citrulline Acts as the "Trojan Horse"
L-citrulline does not get broken down by intestinal or liver arginase. It slips freely past the liver into the bloodstream and heads straight to the kidneys. There, specialized enzymes (argininosuccinate synthetase and argininosuccinate lyase) transform citrulline into pure L-arginine inside your tissue capillaries (Curis et al., 2005).
3. Better Vasodilation and Ammonia Clearance
By combining both amino acids, Arginine and Citrulline 500 / 250 delivers an immediate spike in plasma arginine alongside a sustained, time-released supply created through the citrulline-arginine pathway. Once inside the vascular endothelium, the enzyme endothelial nitric oxide synthase (eNOS) uses arginine to synthesize nitric oxide gas (NO). Nitric oxide signals arterial walls to relax (vasodilation), expanding blood vessel diameter for smoother blood flow, lower vascular resistance, and efficient waste removal (Palmer et al., 1987). Furthermore, citrulline plays a critical role in the urea cycle, sweeping away fatiguing ammonia produced during high-intensity weightlifting and endurance cardio.
Published Scientific References Supporting This Ratio:
Morita, M., et al. (2014). "Oral supplement of L-citrulline and L-arginine increases arterial blood flow in humans." Biochemical and Biophysical Research Communications, 454(1), 53-57. (Demonstrated that combined supplementation raised blood flow and nitric oxide markers more effectively than either alone).
Suzuki, T., et al. (2017). "The effects of combined oral L-citrulline and L-arginine supplementation on blood flow and exercise performance." Journal of the International Society of Sports Nutrition, 14(1), 45.
Schwedhelm, E., 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.
Curis, E., et al. (2005). "Almost all about citrulline in mammals." Amino Acids, 29(3), 177-205.
NOW Foods Quality: Stringent Lab Testing & Heavy Metal Screening
Cheap amino acid powders flooding online marketplaces often suffer from synthetic degradation, unlisted fillers, and heavy metal accumulation. NOW Foods operates one of the most advanced private analytical laboratory facilities in the United States, carrying ISO/IEC 17025:2017 accreditation to ensure exact label accuracy and biological purity.
✓ ICP-MS Heavy Metal Detection
Every production run is screened using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). This instrument detects toxic trace metals—including Lead (Pb), Arsenic (As), Cadmium (Cd), and Mercury (Hg)—down to single parts-per-billion (ppb), complying with California Proposition 65 limits and exceeding standard USP guidelines.
✓ HPLC Potency & Free-Form Identity
Using High-Performance Liquid Chromatography (HPLC), NOW tests raw ingredients to verify the exact chemical fingerprint of free-form L-arginine and L-citrulline. This ensures the raw material has not degraded into inactive precursors and is completely free of undeclared synthetic adulterants.
✓ Comprehensive Microbial Clearance
Bioburden assessments check raw ingredients and finished capsules for Salmonella, E. coli, Staphylococcus aureus, total yeast, and molds. Every finished bottle is certified safe, sterile, and shelf-stable.
✓ Certified cGMP & Non-GMO Standards
Manufactured in facilities independently audited by Underwriters Laboratories (UL) and the Natural Products Association (NPA). Formulated entirely without GMOs, synthetic colors, artificial flow agents, or hidden binding glues.
Verified Supplement Facts & Complete Ingredients
Below is the verified nutritional facts panel directly matched against NOW Foods manufacturing specifications:
Supplement Facts
Serving Size: 1 Veg Capsule
Servings Per Container: 240
Amount Per Serving
% Daily Value
L-Arginine (Free-Form)
500 mg *
L-Citrulline (Free-Form)
250 mg *
* Daily Value not established.
Full Ingredients List
Active Ingredients: L-Arginine (Free-Form) 500 mg, L-Citrulline (Free-Form) 250 mg.
Other Ingredients: Hypromellose (plant-derived cellulose capsule), Stearic Acid (vegetable source), and Silicon Dioxide.
Allergen Free Guarantee: Not manufactured with wheat, gluten, soy, milk, egg, fish, shellfish, tree nut, or sesame ingredients. Produced in a GMP facility that processes other ingredients containing these allergens. Suitable for vegetarians and vegans.
Practical Usage Guidelines & Timing
Standard supplement bottles give minimal direction. Over decades of clinical feedback and athletic use, here is how to get the most out of your servings:
For General Cardiovascular & Blood Flow Support: Take 1 veg capsule 2 times daily. For the best absorption, take your capsules between meals with a glass of water.
For Pre-Workout Training Pumps & Endurance: Take 2 to 4 capsules approximately 45 to 60 minutes prior to your resistance training or cardio session. This timeframe allows citrulline to peak in plasma right as vascular workload increases.
Empty Stomach Consideration: Free-form amino acids compete with dietary proteins for transport in your intestines. Taking this supplement at least 30 minutes before food or 2 hours after a heavy protein meal delivers maximum bioavailability.
Important Health Warnings, Drug Interactions & Edge Cases
Because L-arginine and L-citrulline directly modify vascular tension and viral replication mechanisms, certain individuals should exercise caution or avoid this product entirely:
Do not take this supplement without consulting your cardiologist if you take nitrates (e.g., nitroglycerin), PDE-5 inhibitors (e.g., sildenafil, tadalafil), or antihypertensive medications (ACE inhibitors, beta-blockers). Combining multiple vasodilators can cause an unsafe drop in blood pressure (hypotension).
Herpes viruses require an abundance of L-arginine relative to L-lysine to replicate. If you are prone to cold sores, genital herpes outbreaks, or shingles, supplemental arginine may trigger active flare-ups (Griffith et al., 1987). If you choose to take this formula, consider supplementing with equal or higher amounts of L-lysine to balance intracellular levels.
Individuals with chronic kidney disease or liver failure should not take amino acid supplements without medical clearance due to nitrogen clearance loads. Furthermore, clinical trials advise individuals with a history of acute myocardial infarction (heart attack) or diagnosed glaucoma to avoid supplemental arginine.
*Disclaimer: 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 speak with your qualified healthcare provider before introducing new nutritional supplements.
Why Buy NOW Arginine and Citrulline From VitaNet®, LLC?
In an era of unauthorized third-party warehouse resellers storing vitamins in hot, unregulated containers, choosing where you purchase matters as much as what you buy.
Over 31 Years of Dedicated Supplement Expertise
VitaNet®, LLC is an independent, family-owned retail business operating online continuously since 1995[cite: 1]. We bring over 31 years of direct nutritional retail and biochemistry knowledge to every product we curate[cite: 1].
Direct Factory-Fresh Shipments: We source directly from authorized brand production lines, ensuring climate-controlled storage and optimal potency[cite: 1].
Unconditional 100% Money-Back Guarantee: If you are unsatisfied for any reason, we refund your purchase and even pay the return shipping costs—even on opened bottles[cite: 1].
BBB A+ Accredited Business: Recognized for trustworthy consumer business practices, honest pricing, and real human support[cite: 1].
Real Physical Storefront: Located at 887 Edison Street Northwest, Hartville, Ohio 44632. You can speak to an experienced team member by phone at (330) 877-8786[cite: 1].
Frequently Asked Questions (FAQ)
What is the primary benefit of taking Arginine and Citrulline 500 / 250 together?
Taking them together creates a two-phase release of nitric oxide. L-arginine acts quickly to support blood flow, while L-citrulline bypasses liver breakdown and converts to arginine in the kidneys over several hours. This combination keeps your blood vessels relaxed and flexible much longer than taking either amino acid alone.
When is the best time of day to take this supplement?
For general cardiovascular health and circulation, take 1 capsule twice daily between meals with plenty of water. If you are using this product for exercise performance and muscle pumps, take 2 to 4 capsules roughly 45 to 60 minutes before your workout.
How does NOW test for heavy metals and purity?
NOW tests every batch in ISO/IEC 17025:2017 accredited in-house laboratories. They use Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to check for heavy metals like lead, cadmium, mercury, and arsenic down to parts-per-billion levels. They also use High-Performance Liquid Chromatography (HPLC) to verify active ingredient potency and screen out synthetic adulterants.
Can this supplement cause cold sores or herpes flare-ups?
Yes, it can in susceptible individuals. The herpes simplex virus requires arginine to replicate. When dietary or supplemental arginine significantly outnumbers L-lysine in the body, it can trigger an outbreak. If you are prone to cold sores, consult your doctor or pair your regimen with an equivalent dose of L-lysine.
Is this product safe to take alongside blood pressure medication?
You must consult your physician before combining this product with prescription antihypertensives, nitrates, or erectile dysfunction medications. Because both arginine and citrulline promote natural vasodilation, taking them alongside prescription blood pressure medications may cause your blood pressure to drop lower than intended.
Are these capsules vegetarian and vegan friendly?
Yes. The formula uses hypromellose (a plant-derived cellulose capsule shell) and vegetable-source stearic acid. It contains no animal gelatin and is completely free from wheat, gluten, soy, dairy, egg, fish, shellfish, tree nuts, and sesame.
