Looking to support healthy blood pressure, enhance muscle pumps during training, or improve vascular blood flow? NOW® ARGININE 500mg delivers pharmaceutical-grade, pure free-form L-Arginine in flexible 500 mg vegetarian capsules. Free-form means this amino acid requires no preliminary digestion, allowing your body to quickly absorb and convert it into nitric oxide.
Quick Product Snapshot
Active Ingredient:
L-Arginine (Free-Form) – 500 mg per capsule (1,000 mg per 2-capsule serving)
Serving Size & Count:
2 Veg Capsules (50 Servings / 100 Capsules per bottle)
Primary Function:
Nitric oxide production, vasodilation, urea cycle detox, and muscle recovery
✓Easy-to-Swallow Convenience: Avoid giant horse pills. These smaller 500 mg capsules let you fine-tune your exact dosage. ✓Pure L-Enantiomer: Formulated using bio-identical L-Arginine that matches human metabolic pathways. ✓Double-Tested Cleanliness: Screened for heavy metals, microbials, and synthetic adulterants in ISO 17025 accredited labs.
What Is L-Arginine 500mg and How Does It Work in the Human Body?
Arginine is what medical science calls a conditionally essential amino acid. Under typical resting conditions, your body synthesizes small amounts of arginine internally, and you absorb more through protein-rich foods like poultry, fish, seeds, and nuts. However, during periods of physical exertion, athletic training, wound healing, or cardiovascular stress, your body’s demand for arginine often outpaces what it can produce on its own.
1. The Nitric Oxide (NO) Pathway: Relaxing Your Blood Vessels
Think of your blood vessels like flexible garden hoses. When the muscular walls around those hoses tighten, water pressure shoots up, and fluid struggles to get through smoothly. The microscopic lining of your arteries—called the vascular endothelium—uses an enzyme known as endothelial nitric oxide synthase (eNOS) to convert L-arginine into a gas called nitric oxide (NO).
Nitric oxide acts as your body’s natural relaxation signal. It tells the smooth vascular muscle tissue to unwind and expand—a biological process known as vasodilation. By widening the vessel diameter, nitric oxide supports:
Lower vascular resistance: Allows blood to flow with less effort, helping maintain healthy blood pressure levels already within a normal range.
Nutrient and oxygen delivery: Transports energy and oxygen directly to hard-working skeletal muscles and critical organs.
Athletic performance and "muscle pumps": Improves blood pooling in active muscle tissue during resistance training, aiding endurance and post-exercise recovery.
2. The Urea Cycle: Clearing Out Metabolic Waste
Beyond blood circulation, L-arginine plays a vital role in your liver's urea cycle. When your body digests proteins or breaks down muscle tissue during heavy workouts, it produces ammonia—a natural but toxic cellular byproduct that causes fatigue. L-Arginine acts as a carrier substrate in the urea cycle, helping your liver convert ammonia into harmless urea, which your kidneys can safely filter out through urine.
Clinical Evidence & Health Benefits: What Does the Research Say?
Unlike many trending supplements supported only by animal studies, oral L-Arginine has been scrutinized in dozens of randomized, double-blind, human clinical trials. Below are key findings from peer-reviewed medical literature:
Blood Pressure Support (Clinical Meta-Analysis)
In a landmark meta-analysis published in the American Heart Journal (Dong et al., 2011; PMID: 22137067), researchers pooled data from 11 double-blind, randomized placebo-controlled trials. The study concluded that oral L-arginine supplementation significantly reduced systolic blood pressure by an average of 5.39 mm Hg (95% CI: -8.54 to -2.25) and diastolic blood pressure by 2.66 mm Hg (95% CI: -3.77 to -1.54).
Citation: Dong JY, Qin LQ, Zhang Z, et al. Effect of oral L-arginine supplementation on blood pressure: a meta-analysis of randomized, double-blind, placebo-controlled trials. Am Heart J. 2011;162(6):959-965.
Endothelial Health & Flow-Mediated Dilation (FMD)
An umbrella systematic review published in the Journal of Chiropractic Medicine (McRae, 2016; PMID: 27660594) evaluated multiple meta-analyses regarding vascular health. The review confirmed that oral L-arginine improves brachial artery flow-mediated dilation (FMD)—the gold-standard clinical ultrasound measurement of how well blood vessels dilate in response to blood flow—by 1.98% to 2.2%, directly confirming enhanced endothelial nitric oxide synthesis.
Citation: McRae MP. Therapeutic Benefits of l-Arginine: An Umbrella Review of Meta-analyses. J Chiropr Med. 2016;15(3):184-189.
Countering Asymmetric Dimethylarginine (ADMA)
As we age or experience elevated cholesterol, our bodies produce higher amounts of ADMA—a natural compound that acts like a false key jamming the eNOS engine, blocking nitric oxide production. Clinical research demonstrates that oral L-arginine supplementation raises the circulating L-arginine-to-ADMA ratio, effectively outcompeting ADMA to restore smooth vascular dilation and healthy tissue microcirculation.
Citation: Böger RH. The pharmacodynamics of L-arginine. J Nutr. 2007;137(6 Suppl 2):1650S-1655S.
NOW Foods Quality Standards: Advanced Lab Testing & Contaminant Screening
Amino acid supplements vary widely in purity across online marketplaces. Many budget brands rely on third-party contract manufacturers without verifying raw material identity or checking for heavy metals. NOW Foods takes an entirely different approach by operating one of the largest private analytical testing complexes in North America (over 45,000 square feet of laboratory space across Bloomingdale, Illinois and Sparks, Nevada).
Heavy Metal Testing (ICP-MS)
Every raw lot is screened using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). This technology detects lead, arsenic, cadmium, and mercury down to parts-per-billion (ppb) thresholds, verifying compliance with USP limits and strict California Proposition 65 standards.
Chiral Purity & Identity (HPLC / FTIR)
NOW uses Fourier Transform Infrared Spectroscopy (FTIR) to verify raw material molecular fingerprints against botanical and chemical standards. High-Performance Liquid Chromatography (HPLC) and polarimetry verify 100% active L-enantiomer stereospecificity, ensuring no inactive synthetic D-isomers are present.
Microbiological & Contaminant Guard
Automated bio-burden testing screens every production run for pathogens including Salmonella, Escherichia coli, and Staphylococcus aureus, alongside total aerobic plate counts, yeast, mold, and residual chemical solvents via Gas Chromatography (GC-MS).
Accreditation & Oversight: NOW’s testing laboratories are ISO/IEC 17025:2017 accredited by the American Association for Laboratory Accreditation (A2LA) for chemical and microbiological testing. Their production plants maintain ongoing UL Dietary Supplement cGMP Certification and have maintained an "A" rating from the Natural Products Association (NPA) since 2000.
Complete Supplement Facts & Ingredient Profile
Transparency matters when you put a supplement in your body. Below are the official supplement facts and complete ingredient statements for NOW Foods L-Arginine 500 mg (Item # N0030 / UPC: 733739000309):
Supplement Facts
Serving Size: 2 Veg Capsules
Servings Per Container: 50
Amount Per Serving
% Daily Value
L-Arginine (Free-Form)
1 g (1,000 mg)*
* Daily Value not established. (Provides 500 mg of Free-Form L-Arginine per individual capsule).
Other Ingredients:
Hypromellose (cellulose capsule), Stearic Acid (vegetable source), and Silicon Dioxide.
Allergen & Clean Label Declarations:
Not manufactured with wheat, gluten, soy, milk, egg, fish, shellfish, or tree nut ingredients. Produced in a GMP facility that processes other ingredients containing these allergens.
Formulation Note: Earlier manufacturing runs utilized bovine gelatin capsules. NOW Foods updated this product code (N0030) to vegetable cellulose (hypromellose) capsules, making it 100% vegetarian, vegan, and plant-based friendly.
How to Take L-Arginine 500mg: Dosage, Timing & Practical Absorption Tips
Suggested Everyday Usage
As a dietary supplement, take 2 capsules twice daily as needed. Take between meals or at bedtime with at least 8 oz. of water or juice to facilitate absorption.
The Practical Absorption Mistake Most People Make
The product label states to take it with water or juice, but here is what clinical pharmacology shows: never take L-arginine with a protein shake or a high-protein meal.
Your small intestine uses a specific biological gateway (the system y+ transporter) to absorb basic amino acids into your bloodstream. When you take L-arginine alongside protein foods containing L-lysine, L-leucine, or L-valine, those other amino acids compete for the exact same doorway. This significantly reduces the amount of arginine that reaches your circulation.
For Athletic Workouts: Take 2 capsules (1,000 mg) 30 to 45 minutes before training on an empty stomach with water or a carbohydrate beverage.
For Cardiovascular Blood Flow: Take 2 capsules in the morning (30 minutes before breakfast) and 2 capsules at bedtime.
Comparison: L-Arginine 500mg vs. 1000mg vs. L-Citrulline
Easy to swallow; allows dosage titration from 500 mg up to 2,000 mg
L-Arginine 1000mg Tabs
Moderate (45–75 minutes)
High-dose cardiovascular protocols
Fewer pills to swallow, but tablets are significantly larger and harder to swallow
L-Citrulline
Sustained (Bypasses liver arginase)
All-day sustained plasma nitric oxide levels
Converts into arginine inside kidneys; excellent when paired with arginine
Critical Medical Safety, Drug Interactions & Contraindications
While L-arginine is an amino acid naturally found in dietary foods, concentrated supplemental doses have real physiological effects on vascular tone and immune activity. If you have any of the following conditions or take any of the following medications, please review these essential health precautions:
The herpes simplex virus requires cellular arginine to replicate and assemble viral proteins, whereas another amino acid—L-lysine—antagonizes viral growth. Taking supplemental L-arginine can trigger cold sore recurrences or flare-ups in HSV-prone individuals. If you feel a tingling sensation or are prone to outbreaks, discontinue use or consult your physician.
2. Prior Heart Attack (Myocardial Infarction)
Do not use if you have had a recent myocardial infarction (heart attack) or have established advanced coronary artery disease. In the clinical VINTAGE MI trial (JAMA 2006; PMID: 16403930), post-heart attack patients receiving supplemental L-arginine experienced higher adverse cardiovascular risks. Always follow your cardiologist's advice.
3. Blood Pressure Medications & PDE-5 Inhibitors
Because L-arginine lowers vascular resistance via nitric oxide, taking it alongside prescription antihypertensive drugs (ACE inhibitors, beta-blockers, ARBs) or erectile dysfunction medications (sildenafil, tadalafil) can produce an additive effect, causing blood pressure to drop excessively (hypotension). Monitor your blood pressure closely.
4. Asthma, Kidney Disease & Scheduled Surgeries
Arginine may worsen airway inflammation in individuals with severe allergic asthma. In individuals with chronic kidney disease, excess amino acid intake can elevate potassium levels (hyperkalemia). If you are scheduled for surgery, discontinue L-arginine at least 2 weeks prior to avoid hemodynamic instability during anesthesia.
Why Buy NOW Foods From VitaNet®, LLC?
When purchasing supplements online, you need confidence that the product on your doorstep is authentic, fresh, and properly stored. Here is why tens of thousands of health-conscious customers trust VitaNet®, LLC:
Serving Customers Since 1995
VitaNet®, LLC is an independent, family-owned health retailer established in 1995 with over 31 years of nutritional industry experience[cite: 1].
100% Risk-Free Guarantee
We offer an unconditional 100% money-back guarantee on all products, even opened items, and we even pay the return shipping cost[cite: 1].
BBB Accredited & Real Support
We are an accredited BBB A+ business based in Hartville, Ohio[cite: 1]. You can reach real customer service staff toll-free at 1-800-877-8702 or (330) 877-8786[cite: 1].
FDA 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.
Frequently Asked Questions (FAQ)
What is NOW Arginine 500mg used for?
NOW Arginine 500mg provides free-form L-Arginine, an essential precursor that your blood vessels use to manufacture nitric oxide (NO). It is primarily used to support healthy circulation, maintain blood pressure levels within normal ranges, aid muscular recovery, and support the body's natural urea cycle for waste elimination.
How many capsules of NOW L-Arginine 500mg should I take per day?
The standard suggested use is 2 capsules (totaling 1,000 mg) taken 1 to 2 times daily. For best absorption, take them between meals or at bedtime with at least 8 ounces of water or fruit juice.
Can I take L-Arginine 500mg with my protein shake or food?
It is best to take L-Arginine on an empty stomach. When consumed with dietary protein, other amino acids (such as lysine and leucine) compete for the same intestinal absorption transporters, significantly reducing the amount of arginine that enters your bloodstream.
What is the difference between free-form L-Arginine and regular Arginine?
Free-form L-Arginine is an unbound, pure amino acid molecule that does not require enzymatic breakdown from a peptide chain. This allows it to be assimilated and converted into nitric oxide much faster than dietary protein sources.
Are NOW L-Arginine 500mg capsules vegan and allergen-free?
Yes. NOW Foods packages this product in hypromellose (cellulose-based) vegetarian capsules. It is non-GMO, vegan/vegetarian, and produced without wheat, gluten, soy, milk, egg, fish, shellfish, or tree nuts.
Who should avoid taking L-Arginine supplements?
L-Arginine should be avoided by individuals who have suffered a myocardial infarction (heart attack) or have established coronary artery disease. It should also be avoided by people prone to herpes simplex outbreaks (cold sores) unless under medical supervision, and by those taking prescription nitrates or blood pressure medications without prior physician consultation.
