What peptide names actually mean

Three naming systems, not one

Peptide names come from three unrelated places. Some are official generic names issued through a World Health Organization programme. Some are chemical shorthand spelling out the amino acids in the molecule. Some are laboratory or catalogue codes with no standards body behind them at all. Nothing on the label says which kind you are holding.

Put semaglutide, GHK-Cu, BPC-157 and TB-500 side by side and they look like four members of the same family. They are not. They are names produced by three different processes, and the differences between those processes matter more than anything the names have in common.

The first process is the International Nonproprietary Name, or INN, a generic name assigned to a pharmaceutical substance so that every substance is identified by one unique, globally recognised name that is public property rather than anyone's trade mark [1][13]. The programme is run by the World Health Organization and was initiated in 1950 by a World Health Assembly resolution, beginning operation in 1953 when the first list of names was published [1]. Semaglutide is an INN. So are liraglutide, octreotide, ipamorelin and tesamorelin.

The second process is not really a naming system at all. It is chemical shorthand, where the letters in the name are the amino acids in the molecule, written out in the order they appear. GHK-Cu is the clearest example, and the section below unpacks it. Nobody issues these names; they are simply the molecule's own description, which is why two independent labs can arrive at the same one.

The third process is a laboratory or catalogue code: a prefix somebody chose, a hyphen, and a number. BPC-157, TB-500, CJC-1295, GHRP-6 and AOD9604 are all of this kind. A code like that is coined by whoever made or catalogued the compound, so it passes through no naming committee and lands in no register. That is not a small footnote. It is the reason the same compound can appear under two spellings, two numberings and two residue counts depending on who is selling it.

What the ending of an official name tells you

Official generic names are built from a meaningless invented prefix plus a shared ending called a stem, and the stem is the informative part. It marks the family a substance belongs to. Once you know a handful of peptide stems, the last four or five letters of a drug name tell you roughly what it is.

An INN is assembled from two pieces: a fantasy prefix, meaning a deliberately meaningless syllable that distinguishes one substance from its neighbours, and a stem, a string of letters shared by every member of a pharmacological group [2]. Stems can sit at the front, the middle or the end of a name, but most of them are suffixes [2]. This is why drug names rhyme: the rhyme is the classification.

For peptides the master stem is -tide, defined as peptides and glycopeptides [2][1]. Underneath it sit narrower stems for particular families, and these are the ones worth memorising. -glutide marks glucagon-like peptide analogues, the group that includes semaglutide, liraglutide and dulaglutide [1]. -reotide marks somatostatin receptor agonists and antagonists, which is where octreotide and lanreotide come from [1]. -ritide marks natriuretic peptides [1]. Outside the -tide family, -tocin marks oxytocin derivatives and -pressin marks vasopressin derivatives [1].

The growth hormone corner is the one most people in this space actually meet, and it is a nested pair. -relin is defined as pituitary hormone-release stimulating peptides, and inside it -morelin is the narrower stem for growth hormone release-stimulating peptides [1]. That distinction does real work. Sermorelin, tesamorelin, macimorelin and ipamorelin all end in -morelin and all act on growth hormone release; deslorelin, goserelin, nafarelin and triptorelin end in -relin without the -mo- and belong to the luteinising hormone releasing hormone group instead [1]. Those four were added to the 2018 anti-doping prohibited list together, as examples of one category [9]. Ipamorelin was described as a pentapeptide developed as a growth hormone secretagogue, which is exactly what its stem advertises [11].

Stems classify broadly, not precisely, and it is worth knowing where that looseness shows. Semaglutide carries the -glutide stem and is a glucagon-like peptide-1 analogue carrying two amino acid substitutions relative to human GLP-1 and a modification at one lysine [12]. Tirzepatide, which reads as though it belongs to the same group, is listed in the stem book under the general -tide heading rather than under -glutide [1]. The ending gets you into the right neighbourhood. It does not get you to the door.

The United States has its own naming council that works alongside the WHO programme, and it publishes its own approved stem list on the same principle: a shared family name gives immediate recognition, and the council resists inventing new stems because too many stems make the system useless [3].

When the letters are a recipe

GHK-Cu is not a brand or a code. The three letters are the three amino acids in the molecule and the Cu is the copper attached to them. Names of this kind are the most honest ones on the market, because they describe the contents rather than pointing at a catalogue entry somebody else controls.

Amino acids have one-letter and three-letter abbreviations, and a short peptide can simply be spelled with them. GHK is glycyl-L-histidyl-L-lysine, a small naturally occurring tripeptide (a peptide three amino acids long) present in human plasma that can also be released from tissue after an injury, and it was first described in 1973 [4]. The Cu is copper: GHK-Cu is the copper-binding form of that same tripeptide [4]. G, H and K are glycine, histidine and lysine. Read that way, the name is a complete ingredient list.

Longer peptides get written the same way, just with three-letter codes instead of one. BPC-157's sequence is Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val, a pentadecapeptide (fifteen amino acids) with a molecular weight of 1419.55 daltons [5]. Ipamorelin's is Aib-His-D-2-Nal-D-Phe-Lys-NH2, a five-amino-acid chain [11]. Sequences run from the N-terminus, the amino end, to the C-terminus, the acid end, which is why a fragment described as running from residue 177 to residue 191 is a piece taken from the tail of the parent protein.

These sequence names are the ones to trust most, because a sequence is checkable. If two vendors disagree about what GHK-Cu is, one of them is wrong about a matter of fact. If two vendors disagree about what TB-500 is, there is no authority to appeal to.

What the numbers do and do not mean

Sometimes the digits in a peptide name are meaningful and sometimes they are a serial number. There is no way to tell from the outside. The same four-digit shape can encode a residue range, a compound counter in a laboratory notebook, or nothing anybody has ever written down.

Occasionally the number is genuinely descriptive. AOD9604 is the C-terminal fragment of human growth hormone running from amino acid 177 to amino acid 191, with an extra tyrosine added at the N-terminus [10]. There the digits in the associated shorthand really are coordinates: they say which slice of the parent protein you have. Note, though, how quickly that precision erodes in circulation. When anti-doping authorities added growth hormone fragments to the prohibited list, they named AOD-9604 and hGH 176-191 as two separate examples [9], one numbering starting at 176 and the other, in the peer-reviewed characterisation, at 177 [10].

More often the number is a serial. CJC-1295 is a long-acting analogue of growth hormone-releasing hormone; in a pair of placebo-controlled trials in healthy adults aged 21 to 61, a single subcutaneous injection raised mean plasma growth hormone two- to ten-fold for six days or more, and its estimated half-life was 5.8 to 8.1 days [6]. Nothing in that description is encoded in "1295". The same laboratory prefix also appears as CJC-1293, which anti-doping authorities list separately as an example of a growth hormone-releasing hormone [9]. Two compounds, one prefix, four digits apart, and the digits explain none of it.

BPC-157 sits in the same category. The letters stand for Body Protection Compound, and the compound is a fifteen-amino-acid sequence isolated as part of a peptide found in human gastric juice, first introduced and described in 1993 [5]. The literature review that catalogues the peptide gives its sequence, its molecular weight and its origin, and attaches no meaning to the number [5]. Treat the 157 as a label, not as information.

TB-500 is the case that matters most, because there the name actively misleads. It is named after thymosin beta-4, a small protein 43 amino acids long whose activity has been traced to several distinct active sites [8]. One of those sites, the central actin-binding domain at residues 17 to 23 plus one additional amino acid, is the seven-amino-acid sequence LKKTETQ, and a synthetic peptide of just that fragment promoted dermal wound repair in aged mice comparably to the whole parent molecule [7][8]. Anti-doping authorities accordingly list thymosin-beta-4 and its derivatives, "e.g. TB-500", as prohibited growth factors, and the list in force for 2026 still carries that entry: TB-500 is treated as a derivative of the protein, not as the protein [9][14]. So the name tells you which molecule the vial is descended from, and not which piece of it is inside.

The name tells you nothing about approval

An official generic name is assigned during development through a naming procedure, not awarded at approval. Plenty of substances carry a proper stem and have never been approved anywhere, and plenty of banned compounds have perfectly ordinary names. A name is an identifier. It is not a verdict.

This is the misreading with the most money riding on it, so it is worth being blunt. Getting an INN is an application, not an achievement. A company asks the WHO programme for a name, an agreed name is published as a proposed INN, anyone may object during a four-month window, and if nobody does it is republished as a recommended INN [1]. That entire procedure is about identification. No regulator's opinion of whether the substance works or is safe enters into it at any point.

The scale makes the point on its own. By the 2018 edition of the WHO stem book, some 9,824 names had been designated as INN, growing by roughly 200 to 240 new names every year [1]. That is a naming register, not an approvals register, and the two are not the same document.

The reverse holds as well. The compounds on the World Anti-Doping Agency's prohibited list carry names indistinguishable in style from approved medicines: tabimorelin, CJC-1293, AOD-9604, TB-500 and the numbered growth hormone releasing peptides GHRP-1, GHRP-3, GHRP-4 and GHRP-5 were all added to it as examples of prohibited substances [9], and every one of them is still named on the list in force for 2026 [14]. Several of them have textbook-correct stems. That did not help them and it should not reassure you.

One more piece of the system is worth knowing because it explains a daily confusion. In 1993 the World Health Assembly resolved that trade marks should not be derived from INN, and that INN stems should not be used in trade marks, on the reasoning that doing so would compromise patient safety by muddling drug nomenclature [1]. That is why the brand name on the pen and the generic name on the insert deliberately look nothing alike. The mismatch is a safety feature, not a marketing trick.

Reading a peptide name in ten seconds

Look at the shape of the name before you look at anything else. A lowercase word ending in a recognisable stem usually came from a formal naming committee. Capital letters, a hyphen and digits usually came from a laboratory or a catalogue. Neither shape tells you whether the compound works.

The fastest tell is typography. An official generic name is typically a single lowercase word, without a hyphen or digits, and it is built to be pronounceable in many languages: the WHO guidance asks that the letters "h" and "k" be avoided, that "e" be used instead of "ae" and "oe", "i" instead of "y", "t" instead of "th" and "f" instead of "ph" [1]. That is why semaglutide, octreotide and ipamorelin all sound like they were designed by the same committee. They were.

Anything with capitals, a hyphen and a number came from somewhere else. That does not make it fake or dangerous by itself, and some of the best-studied compounds in the field are named that way. It does mean nobody vetted the name, so it will not tell you a family, a mechanism or a molecule size, and you should expect the same compound to appear under inconsistent spellings.

So a practical three-question read. First, what shape is the name: committee word, sequence shorthand, or catalogue code? Second, if it is a committee word, what is the last stem, and does the seller's description match the family that stem denotes? Third, if it is a catalogue code, what molecule does it claim to be, and can the seller give you a sequence? A vendor who cannot tell you what is in the vial in amino acids is a vendor telling you the name and hoping it sounds like enough.