Short answer
A peptide is a short chain of amino acids. It is the same chemistry as a protein, and the difference is one of scale: peptide up to a few dozen amino acids, protein once the chain grows long and folds into a stable three-dimensional structure. The boundary is a convention rather than a fixed threshold, but the order of magnitude is real.
Why the length changes everything
A short chain can be made in a laboratory by standardised synthesis, stored as a lyophilised powder and characterised with ordinary methods: liquid chromatography for purity, mass spectrometry for identity. A long protein needs biological production systems and far more complex control. That is precisely why the compounds discussed across this section are peptides and not proteins.
BPC-157 is fifteen amino acids long. Semaglutide has thirty-one, plus modifications that greatly extend how long it stays in circulation, which is why it is given weekly rather than daily. These are not trivia: length and modification determine stability, half-life and how a vial must be stored.
Why names like BPC-157 or retatrutide appear so quickly
Because peptides are not a single group. They separate by mechanism, and knowing the family is usually enough to place a new name without further reading. Tissue repair covers BPC-157 and TB-500, which are named together not because they are similar but because they describe different stages of the same process: one is associated with new blood vessel formation, the other with actin binding and cell migration. The metabolic family separates by how many receptors are involved: semaglutide one, tirzepatide two, retatrutide three. Skin and connective tissue covers GHK-Cu, a defined complex of a tripeptide and a copper ion.
The distinction that matters more than the chemistry
Some peptides are authorised medicines and reach a patient only through a pharmacy on prescription. Others have no authorisation in any country and are supplied as laboratory reagents. The difference is not in the molecule but in regulatory status and in how the product is presented: a product presented as having curative properties becomes a medicine by that presentation alone, whatever the label says. That is also why no human dosing appears on these pages. The framework is set out on legal information, and the Irish specifics on are peptides legal in Ireland.
Legal information
Medicine versus laboratory reagent, what the HPRA oversees, and what a queried parcel is asked for.
Lab reports
The right place to go if you want to compare basic explanations with documents and batch-level testing.
Research summaries
Background page on research themes, terminology, and the wider site context.