Key facts
- Full name
- CAS Registry Number (CAS RN)
- Assigned by
- Chemical Abstracts Service (CAS), a division of the American Chemical Society
- Format
- Up to 10 digits in three hyphenated parts
- Last digit
- Check digit for error detection
- BPC-157
- 137525-51-0
- Water
- 7732-18-5
What is a CAS number?
A CAS number is a registry identifier. Each time CAS adds a substance to its registry, it hands out the next available number. Nothing is calculated from the structure, so two very similar molecules can have unrelated CAS numbers, and you can't read anything about a substance from its digits.
What makes the number useful is that it's unambiguous. Chemical names shift between suppliers, languages and naming conventions; a CAS number points to a single registered substance. CAS also runs CAS Common Chemistry, an open resource that grew in 2021 from about 8,000 to about 500,000 substances, each with basic properties and a machine-readable structure [1]. On PubChem, CAS numbers appear among the synonyms on each compound record [2].
How is a CAS number structured?
There are three parts, separated by hyphens: a first block of two to seven digits, a middle block of two digits, and a single check digit at the end. Water is 7732-18-5. BPC-157 is 137525-51-0.
How the check digit works
That last digit is there to catch typing errors. Take every digit except the final one and number them from the right, starting at 1. Multiply each digit by its position, add up the products, and keep the last digit of the total. Here's BPC-157:
| Digit (read right to left) | Position | Product |
|---|---|---|
| 1 | 1 | 1 |
| 5 | 2 | 10 |
| 5 | 3 | 15 |
| 2 | 4 | 8 |
| 5 | 5 | 25 |
| 7 | 6 | 42 |
| 3 | 7 | 21 |
| 1 | 8 | 8 |
| Sum | 130 |
The total is 130. Its last digit is 0, which matches the check digit. Every CAS number in the Vinnix compound tables passes this test.
A correct check digit proves only that the number is well formed. It doesn't prove the number belongs to the substance printed next to it, so confirm the pairing against a registry record.
What does a CAS number identify?
A CAS number identifies a substance exactly as it was registered. Closely related forms can therefore carry different numbers, and that is where most of the practical confusion comes from.
- Isomers. Leucine and isoleucine have the same formula, C6H13NO2, but they are registered separately as 61-90-5 and 73-32-5.
- Salts and complexes. A free peptide, its acetate salt and a metal complex can each be a separate registry entry. The number 89030-95-5 belongs to the copper complex GHK-Cu, which is a different substance record from the GHK peptide on its own.
- Alternate numbers. Some substances pick up more than one number over the years. PubChem shows 61-90-5 for L-leucine next to other numbers in its synonym list [2], so confirm the primary number instead of grabbing the first search result.
- Trade names. A name like TB-500 gets used for more than one sequence. If someone quotes a CAS number for a trade name, check it against the sequence actually supplied.
CAS numbers vs. other chemical identifiers
CAS numbers are one identifier among several, and each answers a slightly different question. Read them together and you get a much more reliable picture of what a record describes.
| Identifier | Issued by | How it is assigned | Example (BPC-157) |
|---|---|---|---|
| CAS Registry Number | Chemical Abstracts Service | Registry number for a substance | 137525-51-0 |
| PubChem CID | NCBI (PubChem) | Database record for a structure | 9941957 |
| UNII | FDA Global Substance Registration System | Substance definition to ISO 11238 | Varies by substance |
| InChI / InChIKey | IUPAC standard | Calculated from the structure | Derived string |
| Molecular formula | Not issued | Atom counts; not unique | C62H98N16O22 |
The FDA and NCATS Global Substance Registration System hands out Unique Ingredient Identifiers (UNIIs) under the ISO 11238 substance standard, which was built for complex substances like proteins, peptides and mixtures [3]. The IUPAC InChI works differently: it is computed from the structure, so anyone can generate it on their own [4]. Least specific of all is the molecular formula, which isomers share.
CAS numbers for Vinnix compounds
Each CAS number below comes from a verified PubChem record for a compound in the Vinnix compound library, and every one passes the check-digit test.
| Compound | CAS number | Molecular formula |
|---|---|---|
| BPC-157 | 137525-51-0 | C62H98N16O22 |
| GHK-Cu | 89030-95-5 | C14H23CuN6O4+ |
| KPV | 67727-97-3 | C16H30N4O4 |
| Ipamorelin | 170851-70-4 | C38H49N9O5 |
| SS-31 | 736992-21-5 | C32H49N9O5 |
| MOTS-c | 1627580-64-6 | C101H152N28O22S2 |
| Sermorelin | 86168-78-7 | C149H246N44O42S |
How should you use a CAS number when reading documents?
Treat the CAS number as a cross-reference that ties a name to a registered substance. Then check that the other identifiers agree.
- Match the CAS number against the compound name and molecular formula on the same document.
- Confirm the form: free peptide, salt or complex.
- Look the number up in PubChem or CAS Common Chemistry and compare the structure or sequence you find there.
- Keep in mind what the number can't do. A CAS number on a label tells you what a material is supposed to be. What's actually in a sample only shows up through analysis, and that's the job of the certificate of analysis and the methods described under peptide testing.
To work through the rest of a report step by step, see how to read a COA.
FAQFrequently asked questions
What does CAS stand for?
Chemical Abstracts Service, a division of the American Chemical Society that has been indexing chemical literature for more than a century. The formal name is CAS Registry Number, often shortened to CAS RN. CAS assigns one when it registers a substance, and the numbers are used worldwide in databases, regulatory documents and product records.
Is a CAS number unique?
In one direction, yes: each CAS number points to one registered substance. The reverse doesn't always hold. Some substances have collected alternate or older numbers, and closely related forms such as salts, hydrates or stereoisomers usually get numbers of their own. When accuracy matters, confirm the primary number and the form in a registry record.
What is the CAS number for BPC-157?
It is 137525-51-0, which appears among the identifiers on the PubChem record (CID 9941957) and passes the CAS check-digit test. The number refers to the peptide with sequence GEPPPGKPADDAGLV and formula C62H98N16O22. Salt forms may be registered differently, so confirm which form a product record actually describes.
Can a substance have more than one CAS number?
Yes. Alternate numbers build up over time, and different forms of a compound, such as a free acid, a salt or a specific stereoisomer, are often registered separately. PubChem, for instance, lists more than one CAS-format number among the synonyms for L-leucine. It's worth checking the primary number against a trusted registry.
Does a CAS number prove what is in a sample?
No. A CAS number tells you which substance a document or label is talking about; it isn't a measurement. Whether a sample really matches that substance is a question for analytical testing, typically mass spectrometry for identity and HPLC for purity, reported on a certificate of analysis tied to a specific batch.
What is the difference between a CAS number and a PubChem CID?
A CAS number is a registry identifier from the Chemical Abstracts Service. A PubChem CID is the record number for a chemical structure in PubChem, the free database run by the US National Center for Biotechnology Information. Most substances have both; for BPC-157 they are 137525-51-0 and 9941957. PubChem lists CAS numbers among each record's synonyms.
REFScientific references
-
Jacobs A, Williams D, Hickey K, et al. CAS Common Chemistry in 2021: expanding access to trusted chemical information for the scientific community. J Chem Inf Model. 2022;62(11):2737-2743. PubMed 35559614
database (CAS registry resource) -
Kim S, Chen J, Cheng T, et al. PubChem 2025 update. Nucleic Acids Res. 2025;53(D1):D1516-D1525. PubMed 39558165
database (PubChem description) -
Peryea T, Southall N, Miller M, et al. Global Substance Registration System: consistent scientific descriptions for substances related to health. Nucleic Acids Res. 2021;49(D1):D1179-D1185. PubMed 33137173
database (FDA/NCATS substance registry) -
Heller SR, McNaught A, Pletnev I, et al. InChI, the IUPAC International Chemical Identifier. J Cheminform. 2015;7:23. PubMed 26136848
standards paper (chemical identifiers)
Documentation
Compound Library
Peptides