Supplement analysis backed by scientific evidence · PT

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Moderate evidenceHeart & metabolic

L-Arginine

Arginine is the direct substrate for nitric oxide, but oral arginine is heavily degraded in the gut and liver before it reaches circulation, which is why citrulline usually outperforms it. It does modestly lower blood pressure; the pump-and-performance claims are much weaker.

What the science says

  • Lowering blood pressure Moderate evidence

    A 2022 dose-response systematic review and meta-analysis of randomised trials found L-arginine supplementation significantly reduced both systolic and diastolic blood pressure, with reductions on the order of a few mmHg and larger effects in hypertensive participants. This is the best-supported arginine claim, though the magnitude is modest and typically requires 4-6 g/day or more.

  • Improving aerobic performance and VO2max Limited evidence

    A 2021 systematic review and meta-analysis found no significant overall effect of L-arginine supplementation on maximal oxygen uptake. Acute ergogenic trials are inconsistent, and the first-pass metabolism problem means oral arginine raises plasma arginine far less efficiently than citrulline does.

  • Erectile function Moderate evidence

    Small randomised trials of arginine, usually at 3-6 g/day and often combined with pycnogenol or other agents, report improvements in erectile function scores in men with mild-to-moderate ED. Trials are small, frequently use combination products, and effects are well below those of PDE5 inhibitors.

  • "Muscle pump" and hypertrophy Limited evidence

    Despite being the original pre-workout "NO booster," arginine has little controlled evidence for increased blood flow at practical oral doses, and no good evidence for added hypertrophy. Growth-hormone spikes reported after intravenous arginine do not occur meaningfully with oral dosing and would not drive muscle growth anyway.

Dosage & safety

Studied doseBlood pressure trials typically use 4-24 g/day in divided doses, with most benefit at 4-6 g/day or above. Erectile function studies use 1.5-6 g/day. Single doses above ~9 g commonly cause GI symptoms; L-citrulline at 3-6 g/day raises plasma arginine more effectively than arginine itself.
SafetyDiarrhoea, nausea and bloating are common above 9-10 g/day. Arginine can lower blood pressure additively with antihypertensives, nitrates and PDE5 inhibitors — combine only with medical advice. Do NOT use after a recent myocardial infarction: the VINTAGE MI trial found higher mortality in post-infarction patients given arginine. May reactivate herpes simplex in susceptible people. Caution in asthma (inhaled/oral arginine can worsen airway inflammation), and in kidney or liver impairment. Not a banned substance.

Scientific references

Where to buy

Vitacost, L-Arginine & L-Ornithine, 100 Capsules

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