A peptide is a chain of amino acids joined by amide (peptide) bonds. Convention puts the cutoff around fifty residues: below that, peptide; above it, protein. The distinction is practical, not mystical. Shorter chains can be synthesized on resin, purified by HPLC, and lyophilized into a stable cake. Longer chains usually need a cell.
Each residue has a one-letter code. Read a sequence N-terminus to C-terminus, left to right. GEPPPGKPADDAGLV is BPC-157. AEDG is Epithalon. The letters are the compound. Everything else — vial size, brand name, forum lore — is packaging.
Why they are fragile
Peptide bonds hydrolyze. Methionine and tryptophan oxidize. Asparagine deamidates. Disulfides scramble. This is why research peptides ship as lyophilized powders, why they live in a freezer, and why reconstituted solutions have a clock on them.
Small-molecule drugs can sit on a shelf in a blister pack. Peptides are closer to food: they are sequences of biology, and biology decays.
How to read a monograph
When Vought lists a peptide, the useful fields are sequence, molecular weight, CAS, and half-life. ‘Typical research reconstitution’ is arithmetic, not a recommendation. Mechanism copy is a map of published pathways, not a promise that those pathways fire in any particular organism.
If a page does not cite a receptor, a mass, or a sequence, it is marketing.