The basics
What is a peptide?
A peptide is a short chain of amino acids. Those are the same building blocks that make up proteins, just far fewer of them. That is the whole idea. Everything else is detail.
The one-sentence version
If amino acids are letters, a peptide is a short word and a protein is a long paragraph. Your body already makes thousands of peptides to carry messages between cells. They tell you when you are full, help wounds heal, and nudge hormones up or down.
A bit more precisely
A peptide is two or more amino acids joined by peptide bonds. The rough convention is simple. Up to about 50 amino acids and we call it a peptide. Beyond that it folds into a complex shape and we call it a protein. Insulin sits right on that boundary at 51 amino acids. It is a good reminder that the word covers some of the most important medicines ever made.
The fuller picture
Peptides are signalling molecules. Because they are small and specific, they bind to receptors with great precision. That is why drug developers like them. It is also why an unregulated market has grown up around the ones that have not been through that process. Synthetic peptides can copy a natural hormone, like the GLP-1 weight-loss drugs. They can also copy a fragment of a larger protein, like BPC-157. What they do depends on which receptors they hit and how long they survive in the body.
The part that matters most
Two worlds, one word
Licensed medicines
A few peptides have been through large human trials and are approved, prescribed and regulated. The GLP-1 weight-loss and diabetes drugs are the obvious example, along with insulin. We know a great deal about these.
Research chemicals
Most peptides discussed online have been studied mainly in animals. They are not approved for human use and they sell in a legal grey area, labelled “for research only”. The science can be interesting. It is also nowhere near settled.
Every entry on this site tells you which world a peptide lives in, and grades it from A to F by how much we actually know in humans.
See how the grading works →This page is educational and not medical advice. Most peptides on this site are not licensed medicines in the UK.