Amino acids & related
L-Leucine
Names you may see: leucine BCAA branched chain amino acid
The quick take
Leucine is an essential amino acid and one of the three branched-chain amino acids, alongside isoleucine and valine.
A closer look
What forms will I see on a label?
It can appear on its own or in BCAA, EAA and protein products. A blend’s ratio does not show the amount of every amino acid unless amounts are declared.
Why people use it
Chosen for muscle-building goals because of its role in muscle protein synthesis; also included in BCAA blends.
These are common goals and marketing uses. The evidence section below explains what research supports.
What does the evidence tell us?
Leucine participates in muscle-protein synthesis, but building protein requires the other essential amino acids too. Total dietary protein remains important.
What should I know before using it?
Follow the directions and cautions on the specific product. Ask a pharmacist about suitability if you take medication or have a medical condition.
Sources & further reading
NIH Office of Dietary Supplements ↗
Content reviewed: September 30, 2026
General educational information. Follow the product label and seek individual advice when needed.