How Peptides Are Named: INNs, Research Codes and Synonyms

In plain English

A single peptide can appear in the literature under half a dozen names. One may be a laboratory code from the group that first made it, one may be an official generic name, and the rest may be database entries or old synonyms.

The official generic names are International Nonproprietary Names, or INNs. The World Health Organization (WHO) selects them so that each substance has one unique, globally recognised name that anyone can use freely, because INNs are placed in the public domain ^[1].

INNs are not random. Related substances share a common ending, called a stem, so that anyone reading the name can see which group it belongs to ^{[1, 2]}. Peptides usually end in “-tide” ^[2].

Laboratory codes are different. They are internal labels, often the initials of a company or project plus a number, and they carry no official meaning ^[8].

Because names multiply, the safest identifiers are the ones tied to the structure itself: the amino acid sequence, the molecular formula and the CAS registry number.

The short version

• INNs are public-domain generic names selected by WHO ^[1].
• A stem shows the group a substance belongs to ^{[1, 2]}.
• Codes and nicknames carry no official standing.
• Match material by sequence, formula and CAS number, not by name.

The WHO INN programme

The INN system was initiated in 1950 by World Health Assembly resolution WHA3.11 and began operating in 1953, when the first list of International Nonproprietary Names for pharmaceutical substances was published. The cumulative list now stands at some 7,000 names, growing by about 120–150 new INNs each year ^[1].

Key features of the system ^{[1, 3]}:

Selection follows a formal procedure. A request is submitted to WHO or through a national nomenclature authority, experts agree a name, and it is published as a proposed INN. Anyone may comment or object during a four-month period. If no objection is raised, the name is published as a recommended INN ^[2]. In 1993 the World Health Assembly endorsed resolution WHA46.19, stating that trade marks should not be derived from INNs and that INN stems should not be used in trade marks ^[2].

WHO’s criteria also shape how names sound and what they may imply: INNs should be distinctive in sound and spelling, not inconveniently long, and names likely to convey an anatomical, physiological, pathological or therapeutic suggestion should be avoided. To make pronunciation possible across languages, the letters “h” and “k” are avoided, “e” is used instead of “ae” and “oe”, “i” instead of “y”, “t” instead of “th” and “f” instead of “ph” ^[2].

Naming biological substances is harder than naming small molecules, and WHO has had to develop separate schemes, including one-word and two-word approaches for different categories such as fusion proteins and monoclonal antibodies ^[5].

Stems: how a name shows a group

A stem is a syllable that marks the pharmacologically related group to which a name belongs. WHO publishes the full list, with definitions, in Use of stems in the selection of International Nonproprietary Names (INN) for pharmaceutical substances ^[2]. Where possible, a new INN includes the stem for its group ^[2].

Peptide-relevant stems, with WHO’s own definitions ^[2]:

Two practical cautions. First, the WHO list itself records cases where a preferred stem was used but not in accordance with its definition, and cases where a substance belongs to a group yet carries no stem at all ^[2]. A stem is therefore a strong hint, not a guarantee. Second, a stem says nothing about quality, legality or whether a substance is approved anywhere.

Systematic naming: structure instead of a label

Alongside generic names sit systematic names, which describe the molecule rather than labelling it.

• Sequence notation. The IUPAC–IUB Joint Commission on Biochemical Nomenclature set out the standard symbols for amino acids and peptides, including the three-letter and one-letter codes ^[6]. Bradykinin is written Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg, or RPPGFSPFR ^[9]. For how to read these strings, including modifications, see Reading a Peptide Sequence.
• Full systematic peptide names spell out each residue: bradykinin is also listed as L-arginyl-L-prolyl-L-prolylglycyl-L-phenylalanyl-L-seryl-L-prolyl-L-phenylalanyl-L-arginine ^[9].
• IUPAC-style chemical names describe the connectivity atom by atom, which for a nine-residue peptide runs to several lines ^[9]. They are unambiguous and almost unusable in conversation, which is exactly why generic names exist.

Laboratory and company codes

Before a substance has an INN it has a code. The usual pattern is a few letters, often the originating company, institute or project, followed by a number, sometimes with a batch or series number as well.

A clean, verifiable example: the somatostatin analogue described in 1982 under the code SMS 201-995 ^[7] later received the INN octreotide ^[2]. PubChem’s entry for octreotide lists both the INN and the code, along with CAS number 83150-76-9 and the molecular formula C₄₉H₆₆N₁₀O₁₀S₂, among 94 synonyms in total ^[8].

Codes create three recurring problems:

1. They look official but are not. A code is an internal label. It does not indicate review by any authority.
2. They drift. The same code is written with and without hyphens or spaces, so one compound appears as several entries. PubChem’s octreotide record alone carries “SMS-201-995”, “SMS 201995”, “SMS 201 995” and “Compound 201-995” ^[8].
3. Some codes embed a claim. Letters in a code sometimes stand for words asserting what the compound is supposed to do in a body. Those expansions are marketing, not nomenclature, and this guide does not expand them.

Registry identifiers: CAS numbers and database synonyms

Registry identifiers are assigned to a structure, not to a name.

CAS Registry Numbers. A CAS Registry Number is a unique and unambiguous identifier for a specific substance. The format is digits separated by hyphens into three parts, and the right-most digit is a check digit used to verify the validity of the whole number. CAS Registry Numbers have been used to identify chemical substances since 1965, and government agencies rely on them in regulatory applications ^[12]. More detail in CAS Numbers and Chemical Identifiers.

PubChem. PubChem is a large integrated public chemical database holding, as of its 2025 update, more than 1,000 data sources, 119 million compounds, 322 million substances and 295 million bioactivities ^[10]. Each compound record (CID) collects synonyms from all of those sources, which is why synonym lists are long: 94 entries for octreotide ^[8], 71 for bradykinin ^[9].

Synonyms are not reliable keys. A study of eight widely used chemical databases quantified how often a non-systematic identifier (a brand name, generic name or other source-assigned label) matches more than one structure. Ambiguity within a single database ranged from 0.1% to 15.2% (median 2.5%), but ambiguity for identifiers shared between databases ranged from 17.7% to 60.2% (median 40.3%). Standardising chemical structures reduced the problem only to a limited extent ^[11].

Match by sequence, CAS number and formula

For anyone checking what a vial is supposed to contain, names are the weakest field on the label and the certificate. The identifiers that can be cross-checked against a database and against analytical data are these:

Worked check, using neutral reference peptides:

• Bradykinin: CAS 58-82-2, formula C₅₀H₇₃N₁₅O₁₁, molar mass 1060.2 g/mol, sequence RPPGFSPFR, PubChem CID 439201 ^[9].
• Angiotensin II: CAS 4474-91-3, formula C₅₀H₇₁N₁₃O₁₂, molar mass 1046.2 g/mol, sequence DRVYIHPF, PubChem CID 172198 ^[13].

If a document gives a name and nothing else, there is nothing to check. If the sequence, formula, mass and CAS number agree with each other and with the analytical data, the identity claim is testable. See How to Read a Peptide COA.

Nicknames and blend names are a red flag

Beyond INNs and codes sits a third layer of naming with no standing at all: invented nicknames, acronyms built from several compound names, and marketing names for mixtures. These names are a problem for three reasons.

• They are not resolvable. A nickname has no CAS number, no formula and no database record, so no one can verify what is in the container.
• They hide composition. A name for a mixture does not state which substances are present, at what proportion, or how each was tested. Identity, purity and content are determined per substance.
• They often encode a claim. Nicknames tend to advertise an intended effect, which is the opposite of what WHO’s naming criteria require of an INN: names likely to convey an anatomical, physiological, pathological or therapeutic suggestion are to be avoided ^[2].

Related reading: Spotting Misleading Peptide Claims and Searching PubMed, which covers searching by every synonym a compound has.

What this means in Australia

• Approved ingredient names are mandatory. All active and excipient ingredients used in therapeutic goods need an Australian Approved Name (AAN). An approved ingredient name is intended to ensure that the name clearly identifies the ingredient, that only one name is used for it, and that names stay consistent with international conventions such as INNs ^[14].
• INN is the preferred reference. For chemical substances, the TGA states that the INN is the preferred reference; where no INN exists, a new name may be proposed using IUPAC naming conventions ^[15].
• The Poisons Standard defines “approved name”. For a poison for human therapeutic use, the approved name is the name in the Australian Approved Names List within the meaning of the Therapeutic Goods Regulations 1990. For other poisons, the instrument sets out a hierarchy that includes names from Standards Australia, ISO and the British Standards Institution, and the international non-proprietary name recommended by WHO ^[16].
• A substance can be scheduled under a name nobody uses. The Poisons Standard itself advises that, if a poison is not found under its approved name, it may appear under a group term: the parent acid of salts (“oxalic acid” to find sodium oxalate), the radical of a salt (“chromates” to find potassium chromate), the element, a chemical group, or a pharmacological group ^[16]. Searching one trade name or nickname is not a scheduling check.
• Labels do not change status. The TGA has stated that a “research use only” disclaimer does not make supply lawful, change a product’s regulatory status, permit importation, or remove advertising or supply obligations ^[17].

This is general information, not legal advice. Laws change; check the current Poisons Standard and TGA guidance.

Frequently asked questions

What is an International Nonproprietary Name?

It is a unique, globally recognised generic name for a pharmaceutical substance or active ingredient, selected by WHO and placed in the public domain so that anyone can use it without restriction ^[1].

What does the ending “-tide” mean in a substance name?

In the WHO stem system, “-tide” marks peptides and glycopeptides, with separate stems for particular groups such as “-pressin”, “-tocin”, “-relin”, “-reotide” and “-actide” ^[2].

Why does one peptide have so many names?

Because different systems name it independently: a laboratory or company code, an INN, national generic names, systematic chemical names and database synonyms. PubChem lists 94 synonyms for octreotide and 71 for bradykinin ^{[8, 9]}.

Is a code name such as “SMS 201-995” official?

No. It is an internal laboratory or company label. The official generic name is the INN, in that case octreotide ^{[2, 7, 8]}.

How should a peptide’s identity be checked?

By comparing the stated sequence, molecular formula, molar mass and CAS Registry Number against a database record and against the analytical data on the certificate of analysis, rather than relying on the name ^{[9, 12]}.

Does a recognised INN mean a substance is approved?

No. An INN is a name. Approval is a separate regulatory decision, and in Australia it means an entry on the Australian Register of Therapeutic Goods ^[17].

References

1. World Health Organization. Guidance on INN: International Nonproprietary Names. who.int. Accessed 25 October 2026.
2. World Health Organization. Use of stems in the selection of International Nonproprietary Names (INN) for pharmaceutical substances, 2024. who.int. Accessed 25 October 2026.
3. World Health Organization. International Nonproprietary Names (INN) programme. who.int. Accessed 25 October 2026.
4. Kopp-Kubel S. International Nonproprietary Names (INN) for pharmaceutical substances. Bull World Health Organ. 1995;73(3):275–279. PMID: 7614659
5. Robertson JS, Chui WK, Genazzani AA, et al. The INN global nomenclature of biological medicines: a continuous challenge. Biologicals. 2019;60:15–23. doi:10.1016/j.biologicals.2019.05.006. PMID: 31130314
6. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN). Nomenclature and symbolism for amino acids and peptides: recommendations 1983. Eur J Biochem. 1984;138(1):9–37. doi:10.1111/j.1432-1033.1984.tb07877.x. PMID: 6692818
7. Bauer W, Briner U, Doepfner W, et al. SMS 201-995: a very potent and selective octapeptide analogue of somatostatin with prolonged action. Life Sci. 1982;31(11):1133–1140. doi:10.1016/0024-3205(82)90087-x. PMID: 6128648
8. National Center for Biotechnology Information. PubChem compound summary for CID 448601, octreotide. pubchem.ncbi.nlm.nih.gov. Accessed 25 October 2026.
9. National Center for Biotechnology Information. PubChem compound summary for CID 439201, bradykinin. pubchem.ncbi.nlm.nih.gov. Accessed 25 October 2026.
10. Kim S, Chen J, Cheng T, et al. PubChem 2025 update. Nucleic Acids Res. 2025;53(D1):D1516–D1525. doi:10.1093/nar/gkae1059. PMID: 39558165
11. Akhondi SA, Muresan S, Williams AJ, Kors JA. Ambiguity of non-systematic chemical identifiers within and between small-molecule databases. J Cheminform. 2015;7:54. doi:10.1186/s13321-015-0102-6. PMID: 26579214
12. CAS, a division of the American Chemical Society. CAS REGISTRY: what is a CAS Registry Number? cas.org. Accessed 25 October 2026.
13. National Center for Biotechnology Information. PubChem compound summary for CID 172198, angiotensin II. pubchem.ncbi.nlm.nih.gov. Accessed 25 October 2026.
14. Therapeutic Goods Administration. Naming ingredients. tga.gov.au. Accessed 25 October 2026.
15. Therapeutic Goods Administration. Naming convention for chemical substances. tga.gov.au. Accessed 25 October 2026.
16. Therapeutic Goods (Poisons Standard—October 2026) Instrument 2026 (F2026L01327). Federal Register of Legislation. legislation.gov.au. Accessed 25 October 2026.
17. Therapeutic Goods Administration. Understanding your responsibilities when importing, compounding and supplying unapproved peptide products. Safety advisory, 13 April 2026. tga.gov.au. Accessed 25 October 2026.