Essential Amino Acids

Essential amino acid supplementation · Essential amino acid supplement

Snapshot

Indications	Contraindications
Sarcopenia^{1, 2} Muscle protein synthesis³ Muscle loss after knee replacement^{4, 5} Hip fracture rehabilitation^6–8 Muscle outcomes in heart failure^{1, 2}	Milk allergy⁹ Soy allergy⁹ Tree nut allergy⁹

Essential amino acids (EAAs) are the nine amino acids the body cannot make in sufficient amounts, including leucine, lysine, and tryptophan¹⁰. Free-form supplements raise blood EAA levels quickly and stimulate muscle protein synthesis (MPS)³. Older adults with reduced anabolic sensitivity are the typical users³.

A systematic review in adults over 60 found limited overall effects on muscle, most consistent for physical performance, and rated the evidence low or very low quality. Randomized trials around total knee arthroplasty found less muscle loss or better muscle recovery with perioperative EAAs^{4, 5, 11}. In a 2025 observational study of older patients with heart failure and sarcopenia, six months of free-form EAAs accompanied improved sarcopenia measures and ejection fraction¹. Products are mainly powders and capsules, sometimes combined with branched-chain amino acids or a multivitamin; see Form comparison.

Per United States (US) product labels, some products carry milk and soy allergen statements⁹. In chronic kidney disease, a 2026 narrative review places EAA and ketoanalogue mixtures within supervised, protein-restricted diets rather than as standalone supplements¹².

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

60 sources, 49 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources