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3Medicinal

L-arginine

Also sold as Arginine, nitric oxide booster

An amino acid sold for blood flow and workouts — poorly absorbed orally, and not appropriate after a heart attack.

TrustedSupp Tier System™ · Tier 3Take as a defined course

Evidence strength

30/100Weak
WEAKLIMITEDMODERATESTRONGVERY STRONG

What the evidence supports: modest blood pressure and blood-flow effects; exercise performance claims are weak.

This scores how well-supported the claim above is — not how much benefit you personally would get. A high score on a narrow claim does not extend to everything the product is marketed for.

How long to take it

Short courses; citrulline is generally a better route to the same goal.

Who it's actually for

Few people. Citrulline raises blood arginine more effectively and is better tolerated.

Safe upper limit

Unverified
No formal upper limit; doses above about 9 g commonly cause digestive upset
Much of an oral dose is broken down before it reaches circulation. In a clinical trial of people after a heart attack, arginine did not help and was associated with more deaths, so it should be avoided in that setting.
No source or citation attached yet.

Interactions to know about

Other supplements:

Run your full list through the interaction check.

Practical notes

  • Avoid after a heart attack — the key trial was stopped early for safety.
  • Adds to the effect of blood pressure medication and nitrates.
  • Some people find it triggers cold sore outbreaks.