Conditionally essential amino acid
Arginine
Limited evidenceA precursor to nitric oxide, though oral supplements are poorly absorbed for that purpose.
What it is
Arginine is used to make nitric oxide, which helps blood vessels relax. The body usually makes enough, but needs can rise during illness or injury.
Food sources
Turkey and chickenPumpkin seedsPeanutsSoy
What the research shows
- Much oral arginine is broken down before reaching circulation, which limits its effect on nitric oxide.
- Performance studies in healthy, trained people are inconsistent.
Read the published research on PubMed →
Food first: most people get what they need from a varied diet with enough total protein. Talk to a provider or registered dietitian before adding a supplement, especially if you take medication or have a health condition.
Similar evidence level
Conditionally essential amino acid
Glutamine
The most abundant amino acid in the blood, often oversold for muscle recovery.
Limited evidenceNonessential amino acidGlycine
The simplest amino acid, a major part of collagen, and studied for sleep.
Limited evidenceNonessential amino acidTyrosine
A building block for dopamine and norepinephrine, studied under acute stress.
Limited evidence