Peptide.

A short chain of amino acids linked by peptide bonds.

A peptide is a short chain of amino acids joined by peptide bonds. Peptides are generally shorter than proteins; the boundary is fuzzy, but chains up to roughly 50 amino acids are usually called peptides. Many of the body's own hormones and signalling molecules are peptides, including insulin, glucagon, GLP-1, growth-hormone-releasing hormone, and oxytocin. That is the reason the category matters here: peptides are not an exotic chemical class invented in a lab, they are the language cells already use to talk to each other, which is why so many of them act on a specific receptor rather than producing a broad, diffuse effect. It also explains their main practical limitation. Because the body is built to digest amino-acid chains, most peptides are broken down quickly by enzymes in the gut and bloodstream, so they are usually studied by injection and often need chemical modification to last long enough to be useful. The common misunderstanding worth correcting is that being a peptide says anything at all about safety or effectiveness. Botulinum toxin and insulin are both peptide-based, and so are many compounds with no meaningful human evidence behind them. The word describes the chemistry of the molecule, not its risk profile, its legal status, or the strength of the research supporting any particular use.