Arginine · 2-amino-5-guanidinopentanoic acid
3000 mg · vegan · gluten-free · 120 caps
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A conditionally essential amino acid and the direct substrate for nitric oxide synthase (NOS), which converts arginine to nitric oxide (NO) and citrulline. Found in meat, poultry, fish, dairy, and nuts — but supplemental doses far exceed dietary intake.
L-arginine is the substrate for endothelial nitric oxide synthase (eNOS), producing NO that dilates blood vessels, improves blood flow, and supports exercise performance. However, oral bioavailability is poor (~40% due to first-pass metabolism by arginase in the gut and liver), which is why L-citrulline — which bypasses this metabolism and is converted to arginine in the kidneys — has largely superseded it in clinical protocols.
People with mild vascular concerns seeking a low-cost NO precursor · those with erectile dysfunction (modest evidence) · older adults with reduced endothelial function · anyone curious about the original NO-boosting amino acid.
Herpes simplex (arginine may promote viral replication — lysine is the better choice), recent heart attack (theoretical concern with NO manipulation post-MI), hypotension (may lower BP further), nitrates and PDE5 inhibitors (potential additive hypotensive effect), kidney disease (arginine is metabolized by the kidneys).
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✓ Pre-workout or split dosing
✓ Pre-workout or split dosing
Flexible — works in any of the above.
Arginine → eNOS → Nitric oxide → Vasodilation → Improved blood flow. The mechanism is elegant, but oral bioavailability is poor due to gut and liver arginase. Citrulline bypasses this bottleneck by converting to arginine in the kidneys.
Vascular and exercise outcomes. The mechanism is stronger than the clinical translation.
Modeled trajectory based on cited keystone trials
Plasma µmol/L. Saturation occurs quickly; higher doses provide diminishing returns due to arginase saturation.
n=50 · 6 weeks · 5 g/day
→ 31% of arginine group vs 12% placebo reported improved erections; improved endothelial function markers
n=80 · 6 months · 3 g/day
→ No improvement in walking distance or vascular function vs placebo in PAD patients
n=41 · 8 days · citrulline malate 8 g/day
→ Reduced fatigue, improved ATP recovery, increased citrulline and arginine plasma levels
C · C+ for erectile dysfunction in mild cases (one positive RCT, modest effect). C for exercise performance (multiple null trials in trained athletes). C for vascular health in PAD (null trial). B− for blood pressure (small, inconsistent reductions). The mechanism is well-characterized but oral bioavailability limits clinical translation. Citrulline is generally preferred.
A plain-English read of the literature behind this supplement. Not a clinical recommendation.
L-arginine was the original nitric oxide booster — the mechanism is elegant, the marketing was enthusiastic, and the clinical reality is more complicated. Arginine is the direct substrate for endothelial nitric oxide synthase (eNOS), which produces NO that dilates blood vessels and improves bl...'t rise proportionally with dose, and why many arginine exercise trials in trained athletes have been disappointing.
The 1999 Chen trial is the most-cited positive study for erectile dysfunction: 50 men with organic ED took 5 g/day for 6 weeks. 31% of the arginine group reported improved erections vs 12% placebo — a real but modest effect. For mild vascular ED, this is a reasonable first-line natural approach. For anything more severe, PDE5 inhibitors are far more effective.
The exercise data is weaker. Multiple trials in trained athletes show minimal to no endurance or strength benefit. The 2006 Wilson trial in peripheral arterial disease (PAD) patients found no improvement in walking distance at 3 g/day for 6 months. The vascular effect is real but doesn't always translate to performance.
The modern consensus has shifted to L-citrulline. Citrulline bypasses first-pass metabolism, is converted to arginine in the kidneys, and achieves higher plasma arginine levels at lower doses. The Pérez-Guisado 2010 trial (cited in the l-citrulline file) showed citrulline malate reduced fatigue and improved ATP recovery during severe training.
Practical guidance: if you're specifically targeting erectile dysfunction, arginine at 5 g/day has modest evidence. For vascular health, exercise performance, or general NO support, citrulline is the better choice. If you already have arginine, it won't hurt — but don't expect dramatic results.
Keystone references: Chen et al. 1999 (BJU Int, PMID 10444158 — erectile dysfunction); Wilson et al. 2006 (J Nutr, PMID 16988130 — null PAD trial); Pérez-Guisado & Jakeman 2010 (J Strength Cond Res, PMID 20386132 — citrulline malate exercise trial, showing why citrulline superseded arginine).
How to use L-Arginine specifically for Fatigue — the right dose, timing, blood markers to track, and how to know if it is working.
A clinical evidence review of L-Arginine — RCT data, effect sizes, evidence grade, and what the numbers mean for your specific situation.
Everything you need to know about L-Arginine — mechanism, dose, safety, buying guide for India, and what the research actually says.
The superior nitric oxide precursor — better absorbed than arginine, with stronger exercise and vascular evidence.
BUY →The most evidence-backed sports supplement — 5g/day increases strength, muscle mass, and emerging cognitive data in aging adults
BUY →The single supplement with the strongest evidence base for a healthy human — if you actually take enough.
BUY →SacredBod's longer take on L-Arginine — context the structured blocks above don't capture.
L-arginine was the original nitric oxide booster — the mechanism is elegant, the marketing was enthusiastic, and the clinical reality is more complicated. Arginine is the direct substrate for endothelial nitric oxide synthase (eNOS), producing NO that dilates blood vessels. The problem is oral bioavailability.
When you swallow arginine, gut and liver arginase metabolize roughly 60% before it reaches circulation. First-pass metabolism is severe. This is why many arginine exercise trials in trained athletes have been disappointing.
The 1999 Chen trial is the keystone positive study for erectile dysfunction: 50 men with organic ED took 5 g/day for 6 weeks. 31% reported improved erections vs 12% placebo — real but modest. For mild vascular ED, this is reasonable. For anything more severe, PDE5 inhibitors are far more effective.
The exercise data is weaker. Multiple trials show minimal benefit. The 2006 Wilson PAD trial found no improvement in walking distance at 3 g/day for 6 months.
The modern consensus has shifted to L-citrulline. Citrulline bypasses first-pass metabolism, converts to arginine in the kidneys, and achieves higher plasma levels at lower doses. For vascular health, exercise performance, or general NO support, citrulline is the better choice.
Practical guidance: arginine at 5 g/day has modest evidence for erectile dysfunction. For everything else, citrulline is preferred.
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