What are peptides?

A peptide is a molecule made of two or more amino acids linked by amide (peptide) bonds. By convention, chains of roughly 2–50 residues are called peptides; longer, folded chains are called proteins. The sequence of amino acids — written from the N-terminus to the C-terminus — determines the peptide's three-dimensional shape and therefore its biological activity.

The distinction is one of size and structure rather than chemistry. Proteins are large, fold into stable tertiary structures and often combine multiple chains; peptides are short, frequently lack a fixed fold, and act largely through binding a specific receptor or surface. That smaller size is what makes synthetic peptides tractable to manufacture by solid-phase synthesis and to characterise precisely.

Research peptides are most usefully grouped by mechanism. The principal classes studied include:

• Growth-hormone secretagogues — GHRH analogues and GHRP/ghrelin-receptor agonists such as Ipamorelin, CJC-1295, Tesamorelin and GHRP-2.
• Incretin and metabolic peptides — GLP-1, dual and triple agonists and amylin analogues such as semaglutide, tirzepatide, retatrutide and cagrilintide.
• Tissue-repair and cytoprotective peptides — BPC-157 and TB-500.
• Copper-binding and matrikine peptides — GHK-Cu and AHK-Cu.
• Neuroactive peptides — Semax, Selank and DSIP.
• Mitochondrial and longevity peptides — MOTS-c, SS-31 and Epitalon.

The full set of compound-level references is catalogued on the research reference index.

Most research peptides are produced by solid-phase peptide synthesis, then purified and freeze-dried (lyophilised) to a stable powder. Identity and purity are the two properties that matter for reproducible work: NMChem characterises every batch by reversed-phase HPLC for purity and by mass spectrometry for identity confirmation, with a per-batch Certificate of Analysis available from the COA database.

All peptides referenced here are supplied as laboratory reference materials, not for human or veterinary use. See Are peptides legal in the UK? for the regulatory background, and each research page for compound-specific identifier data and literature.