Why Peptide Drug Names End in -tide: INN Stems Decoded
Nomenclature
Peptide drug names almost all end in the same four letters, and that is not a coincidence or a fashion. Semaglutide, tirzepatide, exenatide, cetrorelix, desmopressin and tetracosactide are all built to a formal specification, run by the World Health Organization, in which the ending of a generic name is a machine-readable claim about what the molecule is. Learn the endings and a spec sheet becomes considerably less opaque — provided you also know what the endings deliberately do not tell you.
Where peptide drug names come from
Every substance that reaches the point of being a drug candidate gets an International Nonproprietary Name, or INN. WHO assigns them, they are public property, and there are roughly 7,000 of them, growing by 120 to 150 a year. The process has three steps: a manufacturer or inventor applies, WHO's expert group selects and publishes a proposed INN, and after a four-month objection window it is republished as a recommended INN.
Some countries run their own naming bodies — the United States Adopted Names Council is the one you will meet most often — and applications from those countries usually go through them. In practice USAN, the British Approved Name and the Japanese Adopted Name are now identical to the INN with rare exceptions, which we will come to.
The key structural idea is the stem. WHO's own instruction is that an INN should, wherever possible, include a common stem expressing the pharmacologically related group the substance belongs to, and that names likely to convey an anatomical, physiological, pathological or therapeutic suggestion are avoided. So the front of the name is deliberately meaningless and the back of the name carries the payload.
There is a real letter rule, and it is narrower than the version you often see repeated. WHO's general principles say that to help translation and pronunciation, “f” should replace “ph”, “t” should replace “th”, “e” should replace “ae” or “oe” and “i” should replace “y”, and that the letters h and k should be avoided. Only h and k. The principles also ban isolated letters and numbers, and discourage hyphens.
The peptide stems, with their official definitions
The parent stem is -tide, defined as “peptides and glycopeptides”, with a cross-reference to the special peptide families that have their own stems. Those families are where the useful information lives.
| Stem | WHO definition | Examples |
|---|---|---|
| -tide | Peptides and glycopeptides | the parent stem |
| -glutide | Glucagon-like peptide (GLP) analogues | semaglutide, liraglutide, dulaglutide, teduglutide |
| -enatide | GLP-1 receptor agonists based on exenatide (exendin-4) | exenatide |
| -dutide | Oxyntomodulin analogues and other dual GLP-1 / glucagon receptor agonists | survodutide, mazdutide, cotadutide |
| -patide | GIP receptor agonists, with or without GLP-1 activity | tirzepatide |
| -lintide | Amylin receptor agonists, including dual amylin / calcitonin receptor agonists | pramlintide, cagrilintide |
| -relin | Pituitary hormone-release stimulating peptides | goserelin, triptorelin, sermorelin, gonadorelin |
| -relix | Gonadotropin-releasing hormone (GnRH) inhibitors, peptides | cetrorelix, ganirelix, degarelix |
| -pressin | Vasopressin analogues | desmopressin, terlipressin |
| -tocin | Oxytocin derivatives | carbetocin |
| -actide | Synthetic polypeptides with a corticotropin-like action | tetracosactide |
| -paratide | Parathyroid hormone analogues | teriparatide, abaloparatide |
The incretin stems are where people go wrong
Popular writing about this field tends to treat every long-acting injectable in the metabolic space as one thing. The naming system does not, and the distinctions it draws are real.
Two traps are worth naming explicitly.
There is no “-lutide” stem. The stem is -glutide, and the g is doing the work — it stands for GLP. Drop it and you have nothing. There is also no “-atide” stem, despite the shared ending of tirzepatide, teriparatide and exenatide; those three sit under three unrelated stems that happen to end the same way.
-glutide means GLP, not GLP-1. This is the cleanest illustration of why a stem is a class marker rather than a mechanism. Teduglutide carries the -glutide stem and is correctly named, but its FDA label describes it as a glucagon-like peptide-2 analogue for short bowel syndrome, and contains no GLP-1 language anywhere. The stem is not wrong; the common assumption about what it means is. Our article on what GLP-1 is is the place to start if that distinction is unfamiliar.
The agonist / antagonist flip that only looks like a rule
The GnRH pairs are the most quotable example of stem logic: -relin for the agonists (goserelin, triptorelin, leuprorelin) and -relix for the antagonists (cetrorelix, ganirelix, degarelix). One letter, opposite pharmacology, and the labels bear it out — the -relin products are described on their FDA labels as gonadotropin-releasing hormone agonists and the -relix products as GnRH antagonists.
But it is not a general rule about the letter x. -relin is defined broadly as pituitary hormone-release stimulating peptides, which is why it also covers growth-hormone-releasing analogues and thyrotropin-releasing analogues. -relix is defined narrowly as GnRH inhibitors only. The mirror works for the GnRH pairs because of how the two definitions happen to overlap, not because someone designed an agonist-antagonist convention.
The GnRH pairs also contain the best example of an INN and a USAN diverging. The INN is leuprorelin; the US adopted name is leuprolide. The INN carries the stem and is decodable; the US name is not. The same thing happens with the ACTH analogue: the INN tetracosactide tells you it is a synthetic 24-residue corticotropin-like polypeptide from the name alone, while the US name cosyntropin carries no stem at all.
What a stem does not tell you
This is the part that matters most for anyone reading vendor material, because a proper-looking name is easy to mistake for a credential.
- Not approval status. WHO assigns an INN on application, which happens years before a drug is approved and for the very large number of compounds that are never approved at all. Retatrutide and cagrilintide both carry properly assigned INNs and neither has an FDA label.
- Not potency, dose or route. No stem definition anywhere references any of these. The definitions quoted above are purely about structure and receptor class.
- Not quality or legitimacy. The naming process evaluates chemistry and proposed mechanism as submitted by the applicant. It does not assess safety, efficacy, purity or manufacturing. Those are regulator functions, and they are entirely separate.
- Not stable over time. The naming bodies say so themselves — USAN's own note is that definitions of older stems may need modification as new information becomes available.
That last point is easy to underrate. Tirzepatide had an INN for years with no substem at all, sitting ungrouped under plain -tide; the -patide stem was only formalised in February 2026, alongside -lintide. Retatrutide is still in that position today — -trutide exists only as a pre-stem, WHO's explicitly provisional category used to collect issues before a stem is adopted. And the biggest revision of all was the retirement of -mab for monoclonal antibodies in October 2021, split into four new stems that distinguish unmodified, engineered, fragment and multi-specific immunoglobulins.
Brand names carry nothing, on purpose
Ozempic, Wegovy, Rybelsus, Victoza, Saxenda, Mounjaro and Zepbound between them cover exactly three molecules: semaglutide, liraglutide and tirzepatide. That is not sloppiness — it is the system working. WHO states plainly that trade marks cannot be derived from INNs and in particular must not include their common stems, precisely so that the two naming systems stay distinguishable. A brand name encodes a marketed indication and a marketing strategy; it deliberately encodes no chemistry.
The practical consequence for reading any product description: the generic name is the only part of the wording that is subject to an external specification. Everything else — the brand, the descriptor, the claimed class — is written by whoever is selling it.
Frequently asked questions
Does -tide always mean the compound is a peptide?
In an assigned INN, yes — the stem is defined as peptides and glycopeptides. What it does not tell you is size, structure, whether it is cyclised, whether it contains non-natural amino acids, or whether it is a peptide by the strict chemical definition or a small protein. For that distinction, see what counts as a peptide.
Why do semaglutide and tirzepatide have different endings if they do similar things?
Because they do not do the same thing at receptor level. Semaglutide is a GLP-1 receptor agonist and carries -glutide; tirzepatide is a GIP and GLP-1 receptor agonist and carries -patide, a stem specifically defined around GIP receptor activity. The endings encode the receptor profile, which is exactly the information the marketing does not.
Can I tell from the name whether something is approved?
No, and this is the most common misreading. An INN is assigned on application, long before any regulator has seen efficacy data. Plenty of compounds circulating with correct-looking -tide names have never been approved anywhere and in some cases have no human data at all.
What is a pre-stem?
WHO's holding category: a suffix in use but not yet adopted as a formal stem, published so that problems can surface before it is locked in. -trutide for triple GLP-1 / GIP / glucagon agonists is currently a pre-stem, as is -melnotide for melanocortin receptor agonists — the latter shortened from -melanotide during 2026 to reduce name-confusion scoring.
Related reading
- Peptide reconstitution calculator — work out concentration and volume for a given vial.
- Peptide library — reference pages for individual compounds.
References
- World Health Organization. The use of stems in the selection of International Nonproprietary Names (INN) for pharmaceutical substances, 2024. who.int
- World Health Organization. INN stem book addendum, INN Working Document 26.638, 5 February 2026 — the adoption of -patide and -lintide. who.int
- World Health Organization. General principles for guidance in devising International Nonproprietary Names for pharmaceutical substances — the letter rules and the no-therapeutic-suggestion rule. who.int
- World Health Organization. New INN nomenclature scheme for monoclonal antibodies, INN Working Document 22.542, May 2022 — the retirement of -mab. who.int
- American Medical Association. United States Adopted Names approved stems. ama-assn.org
- US FDA / DailyMed. Gattex (teduglutide) prescribing information — a -glutide product that is a GLP-2 analogue. dailymed.nlm.nih.gov
- US FDA / DailyMed. Mounjaro (tirzepatide) prescribing information — GIP and GLP-1 receptor agonist. dailymed.nlm.nih.gov
- US FDA / DailyMed. Cetrotide (cetrorelix acetate) prescribing information — a decapeptide with GnRH antagonistic activity. dailymed.nlm.nih.gov
Informational only — not medical advice. VialHelp does not sell peptides and does not recommend any product, treatment or dose. A drug name tells you nothing about whether a product is safe, legal or fit for any purpose. Discuss any medical question with a qualified healthcare professional. Intended for readers 21+.