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L-Arginine: Uses, Benefits, Dosage & Safety

Last updated: June 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy

Quick summary

L-arginine is an amino acid the body turns into nitric oxide, a molecule that relaxes blood vessels. It is taken for circulation and erectile function, with modest evidence — but there is an important safety warning after a heart attack.

What is L-Arginine?

L-arginine is an amino acid that serves as the raw material for nitric oxide, a signalling molecule that widens blood vessels and improves blood flow. The body makes some and gets more from protein-rich foods. As a supplement it is marketed for circulation, blood pressure, erectile function and exercise 'pumps'. A practical limitation is that much of an oral dose is broken down in the gut and liver before it can act.

What L-Arginine is commonly used for

In supplements, L-Arginine is most often included for men's vitality & testosterone support. It is used as nutritional support, not as a treatment for any medical condition — the distinction matters, because the claims on a sales page are often stronger than the evidence allows.

How L-Arginine works

L-arginine is converted by an enzyme into nitric oxide, which signals the smooth muscle in blood-vessel walls to relax and widen (vasodilation), increasing blood flow. Better blood flow is the rationale for its use in erectile function, blood pressure and exercise performance. Because the gut and liver clear a lot of swallowed arginine, fairly large doses are needed, and results are inconsistent.

What the evidence says

Here's an honest snapshot of what published research suggests about L-Arginine — including where the evidence is limited.

Typical dosage used in studies

Studies have used roughly 3-6 g/day, sometimes more, often split into doses. This is research information, not a recommendation.

Side effects and safety

At moderate doses L-arginine is usually tolerated; higher doses commonly cause digestive upset, including nausea and diarrhoea. It can lower blood pressure, and there is a documented safety concern after heart attack.

Medication interactions and who should avoid L-Arginine

Medication & safety check

People who have had a recent heart attack should avoid L-arginine because of evidence of harm. Those on blood-pressure medication or erectile-dysfunction drugs should be cautious about additive blood-pressure lowering, and people with a history of cold sores or genital herpes sometimes avoid high doses. Check with a doctor if you take any medication.

This is general information, not personal medical advice. If you take any medication, confirm it's safe to combine with L-Arginine with your doctor or pharmacist first.

Sources & further reading

The evidence summary above is drawn from these sources. For general, authoritative background you can also consult:

Frequently asked questions

What is L-arginine used for?

Mainly circulation and erectile function, via nitric oxide. The evidence is modest, and it works better for ED when combined with other compounds.

Is L-arginine safe?

For most people at moderate doses, yes — but it should be avoided after a recent heart attack, where a trial found higher mortality.

Why are large doses needed?

Much of an oral dose is broken down in the gut and liver before it can raise nitric oxide, which is also why L-citrulline is sometimes preferred.

Does it help workouts?

The performance evidence is weak and inconsistent despite the 'pump' marketing.

Can I take it with ED or blood-pressure medication?

Be cautious — the blood-pressure-lowering effects can add up. Check with a doctor first.

Supplements that contain L-Arginine

On FactoWiki, L-Arginine appears in these reviewed products. Each review breaks down the full formula, pricing and safety.