What a peptide actually is

A peptide is a chain of amino acids joined end to end, conventionally between two and fifty of them. Chains longer than that, which fold into a stable three-dimensional shape, get called proteins instead. The line is a convention rather than a law: insulin sits on it at 51 links and gets called the smallest protein or the largest peptide depending on who is writing.

That sounds like trivia, and it is the reason your options look the way they do. Your body already runs on these molecules. The receptor a peptide drug binds was built by evolution for a peptide your own cells make, so a developer is not inventing a new key — they are filing down a copy of one you already carry. That is why these drugs tend to hit one target rather than several, and why a well-made one usually has a narrower side-effect profile than a pill acting on the same system.

It is also why the same word appears on a prescription and on a capsule sold as a supplement. “Peptide” describes the shape of a molecule, not a level of evidence. Nothing about the word tells you which of the two you are looking at — that is what the rest of this page is for.

This is the distinction that decides everything practical, and it does not follow the five families neatly. Semaglutide and tirzepatide are approved drugs with brand names you have heard, and so are liraglutide and PT-141. Tesamorelin is approved too, for one narrow indication. Everything else on the list above is either compounded — mixed to order by a licensed pharmacy against a prescription — or sold in a gray market with no prescription behind it at all.

What that changes for you

An approved drug has a manufacturer, a label, a dose that was tested, and a chance, however small, that insurance touches it. A compounded peptide has a pharmacy and a prescriber standing behind that particular batch, and the published evidence usually stops well short of the marketing. A peptide sold without either has nobody standing behind it, which is a different kind of purchase than the word “peptide” suggests.

The practical consequence for shopping: the compounds with approved products are the ones providers publish prices for, and the ones where the provider you pick is a question of cost and service rather than of whether anyone will write the prescription at all.

One more moving part. The FDA has restricted pharmacy compounding of several of these compounds on safety grounds, and that list is not static — what a pharmacy could mix last year is not automatically what it can mix now. It is worth asking a provider directly rather than assuming, and our state checker covers the layer above it: what your own state adds on top.