Peptide

A peptide is a short chain of amino acids linked together. Anything between 2 and roughly 50 amino acids is a peptide. Above that, it's called a protein. Your body makes thousands of peptides naturally — insulin, oxytocin, glutathione, the pituitary's signaling hormones. When this site says 'peptide,' we mean a synthetic or semi-synthetic peptide that someone is injecting (or applying topically) for a non-trivial reason: weight loss, recovery, sleep, skin, longevity, libido, cognition.