# What is a peptide?

> A peptide is a short chain of amino acids, the building blocks of proteins, and the body makes many. By a 2024 count the FDA had approved about 100 as medicines, but the word alone does not show whether a product is approved, tested in people or even what it contains.

The journal is published by Rovere, a telehealth service that sells some of the treatments discussed here. Articles are general information, not medical advice. Only a licensed clinician can say whether a treatment is right for you.

- Topic: Basics
- Web page: https://roverehealth.com/journal/what-is-a-peptide

## Key points

- Peptides are short chains of amino acids, the building blocks of proteins. No agreed length separates them from proteins, but since March 2020 the FDA has regulated chains of more than 40 amino acids with a defined sequence as proteins.
- The body makes many peptides that act as chemical signals. Glucagon makes the liver release sugar into the blood, for example, and oxytocin makes the uterus contract.
- Most peptide medicines are injected, because digestive enzymes break peptides apart and the gut lets little of what is left into the blood. A few approved peptides are swallowed as tablets or capsules, or sprayed into the nose.
- Official names of peptide medicines often end in -tide, as in octreotide and semaglutide. BPC-157 is a common name, not an official drug name, and the FDA has found different substances sold under it.
- The word “peptide” covers FDA-approved medicines and also products the FDA has not approved. Examples are dietary supplements, products labeled “for research purposes” and compounded peptides, which pharmacies prepare for individual patients.

## What a peptide is

A peptide is a short chain of amino acids, the small molecules that proteins are also built from. A chemical bond called a peptide bond joins each amino acid to the next. Proteins are chains of the same kind, and the difference is mainly size. Peptides are the shorter, simpler chains. [1]

No single length marks the point where a peptide becomes a protein. Dictionaries and textbooks quoted by the FDA in 2018 put the upper limit for a peptide anywhere between 20 and 100 amino acids. One textbook it cited says a chain seems to need at least 40 amino acids to hold a stable folded shape in water. [2, 1]

Since March 23, 2020, an FDA rule has treated any chain of more than 40 amino acids with a defined sequence as a protein. For the FDA, then, a peptide has 40 or fewer amino acids and is generally regulated as a drug. A protein medicine is regulated as a biological product, the category that also includes vaccines. Insulin, with 51 amino acids in two linked chains, became a licensed biological product that day, though scientists often call it a peptide hormone. [3, 1, 4, 5, 6, 7, 8]

Small-molecule drugs are compact chemicals that can usually be swallowed and absorbed. Therapeutic peptides are bigger. Most weigh 500 to 5,000 daltons, a unit of molecular mass, and semaglutide weighs about 4,114 daltons. Peptides tend to attach more precisely to their targets, the molecules they act on in the body, than small molecules do. But they are less stable, and the body clears them quickly. [9, 10]

## Peptides your body makes

Many peptides act as chemical signals in the body, including these four. [5]

- Insulin, 51 amino acids in two chains, is made by beta cells in the pancreas. It signals muscle and fat cells to take up glucose, the main sugar in the blood.
- Glucagon, 29 amino acids, is made mainly by alpha cells in the pancreas. It raises blood sugar by making the liver break down glycogen, its stored form of glucose, and release the glucose into the blood.
- GLP-1 (glucagon-like peptide-1), 30 or 31 amino acids long depending on its form, is released by cells in the lining of the gut as food passes. It prompts the pancreas to release insulin when blood sugar is high, and it slows the emptying of the stomach.
- Oxytocin, 9 amino acids, is released from the pituitary gland, at the base of the brain. It makes the uterus contract and triggers the release of breast milk.

Sources for the list above: [4, 11, 12]

## Peptide medicines

Insulin was the first peptide hormone to be isolated and sold as a medicine. It was isolated in 1921 and sold from 1923, and for decades it was purified from the pancreases of cows and pigs. [4, 9]

A February 2024 review counted around 100 peptides authorized by the FDA since insulin. Many are modeled on a hormone the body makes. Semaglutide, first approved in 2017 for type 2 diabetes, is built on GLP-1. Octreotide mimics the hormone somatostatin. The FDA has approved it to lower growth hormone in acromegaly, a condition in which the body makes too much of it. It is also approved to control severe diarrhea and flushing caused by certain hormone-releasing tumors. [4, 9, 10, 13]

Drug makers often alter a peptide the body makes so that it lasts longer. The body’s own GLP-1 has a half-life, the time it takes for half of it to clear, of about 1 to 2 minutes. An enzyme called DPP-4 cuts it, and the kidneys remove it. One change to semaglutide’s chain protects it from DPP-4, and an added fatty side chain lets it bind to albumin, a protein in the blood. Semaglutide’s half-life is about a week. [4, 11, 10]

The FDA describes three ways to make a peptide: extract it from animal tissue, build it chemically, or have genetically engineered cells produce it. Most synthetic peptides are assembled one amino acid at a time on a solid support, a method called solid-phase synthesis. The peptide chain in approved semaglutide is produced by yeast. Ziconotide, approved in 2004 for severe chronic pain, is a synthetic copy of a peptide from the venom of a cone snail. [5, 6, 14, 10, 9, 15]

## Why most peptide medicines are injected

Swallowed peptides face two barriers. Protein-digesting enzymes in the stomach and intestine break them apart, and the lining of the gut lets little of what survives into the blood. Size is one reason the lining lets so little through. Drug designers treat a weight above 500 daltons as one warning sign that a swallowed drug will be poorly absorbed, and most therapeutic peptides weigh more than that. The 2024 review counted only 11 FDA-approved peptides that can be taken by mouth. [16, 17, 18, 19, 4]

Semaglutide tablets, first approved in 2019, get around this with an added ingredient, salcaprozate sodium (SNAC). Studies by semaglutide’s maker found that, in people and dogs, the drug is absorbed in the stomach, right next to the dissolving tablet. According to those studies, SNAC makes the fluid around the tablet less acidic, which protects semaglutide from pepsin, a stomach enzyme. It also helps semaglutide pass through the cells of the stomach lining. [17, 16, 20]

Even with SNAC, the FDA-approved labels estimate that no more than about 2 in 100 semaglutide molecules in a tablet reach the blood. From an injection under the skin, about 9 in 10 do. Eating soon after the tablet and drinking more water with it both lower absorption, so the labels set strict conditions for taking it. [20, 21, 10]

Orforglipron, a newer GLP-1 drug, is not a peptide. It switches on the GLP-1 receptor, the docking site on cells that GLP-1 and semaglutide act through, and its label allows it to be taken with or without food. The FDA approved it in April 2026 for long-term weight management in adults with obesity, or with overweight and at least one weight-related health problem. [22, 23, 10]

Six peptides that have an FDA-approved form that is not injected. [20, 21, 16, 17, 24, 25, 26, 27, 4, 12, 28, 29]

| Ingredient | How it is taken | FDA-approved for | Why it can be taken this way |
| --- | --- | --- | --- |
| Semaglutide | Tablet | Type 2 diabetes or weight management, depending on the product, and lowering the risk of heart attack, stroke and heart-related death in certain adults | An added ingredient, SNAC, helps a small share cross the stomach lining |
| Octreotide | Delayed-release capsule | Long-term treatment of acromegaly in people who have responded to and tolerated octreotide or lanreotide | A coating keeps the capsule intact through the stomach, and an added ingredient, sodium caprylate, helps it cross the intestinal wall |
| Linaclotide | Capsule | Irritable bowel syndrome with constipation, and chronic constipation with no known cause, in adults and some children | It acts on the inner surface of the intestine and is barely absorbed |
| Cyclosporine | Capsule | Preventing rejection of a transplanted kidney, liver or heart, or treating chronic rejection; one form also for severe rheumatoid arthritis and psoriasis | Its chain forms a ring and includes unusual amino acids, which help it survive stomach and intestinal fluids |
| Glucagon | Powder sprayed into the nose | Severe low blood sugar in people with diabetes aged 1 and older | It is absorbed in the nose, so it never has to pass through the gut |
| Desmopressin | Tablet or nasal spray | Central diabetes insipidus, replacing vasopressin, a hormone that helps the kidneys save water; the tablet also for bedwetting, and for temporary excessive urination and thirst after surgery in the pituitary region or a head injury | The spray is absorbed in the nose. Swallowed, its ring-shaped chain holds up in digestive fluids, but the tablet label estimates that fewer than 2 in 1,000 molecules reach the blood |

## How peptides get their names

In the US, a drug ingredient’s official name is chosen by the United States Adopted Names (USAN) Council. The council, the developer and the World Health Organization’s naming experts must all agree, so that one name is used worldwide. [30]

Names in the same drug family share a common part, called a stem. The stem -tide, at the end of a name, marks a peptide, as in octreotide. Longer forms of it mark narrower families. The ending -glutide marks drugs modeled on glucagon-like peptides, such as liraglutide and semaglutide. The ending -patide, as in tirzepatide, marks drugs that activate the receptor for GIP, another hormone the gut releases with meals. Other peptide families have their own stems, such as -relin for peptides that trigger the release of a hormone and -pressin for relatives of vasopressin, such as desmopressin. [31, 4]

Before it has an official name, a compound goes by a code. Developers can apply for a name during clinical trials, and many wait until phase 2, the middle of the three main stages of testing in people. A phase 2 trial of tirzepatide that began in 2017 is still registered under an official title that calls it only LY3298176. [30, 32]

BPC-157 has no official US name. In a 2026 briefing for its pharmacy compounding advisers, the FDA called it a common name. It also goes by Bepecin and PL-14736. The letters BPC stand for body protection compound, a name University of Zagreb researchers in Croatia gave to a substance they reported finding in stomach juice. In 1993 they described BPC-157 as a 15-amino-acid fragment of it. [14, 33]

The FDA says BPC-157 is not an ingredient of any FDA-approved drug. It has also found several salts and other variants, including different active molecules, sold under that one name. A salt pairs the peptide with a second chemical of opposite charge, such as acetate. The agency calls such inconsistent naming a safety risk, because a patient may be given a different substance from the one the doctor ordered. [14, 30]

The name CJC-1295 has spread to more than one substance. A 2005 paper by researchers at a Montreal company first described CJC-1295, an altered version of the first 29 amino acids of growth hormone-releasing hormone. That hormone tells the pituitary gland to release growth hormone. In a 2024 briefing for its compounding advisers, the FDA counted at least five distinct substances related to CJC-1295, known over time by at least nine names. None is an ingredient of an FDA-approved drug. [34, 35]

## What the word doesn’t tell you

Peptides are also sold as compounded drugs, which are made by mixing or altering ingredients to suit an individual patient. The FDA does not approve compounded drugs or review their safety, effectiveness or quality before they are marketed. The agency has also warned companies that illegally sold unapproved drugs containing semaglutide, tirzepatide or other GLP-1 drug ingredients directly to consumers. The products were falsely labeled “for research purposes” or “not for human consumption”, and the FDA says they are of unknown quality and may be harmful. [36, 37]

The word “peptide” also appears on dietary supplements and cosmetics. Neither needs FDA approval before sale, apart from color additives in cosmetics. The FDA noted in 2026 that BPC-157 is sold in the United States in supplement capsules and tablets. [38, 39, 14]

The FDA warns that building a peptide one amino acid at a time can leave impurities that closely resemble the intended peptide and are hard to detect without specialized tests. Peptides and these impurities can also trigger an immune response, more so when injected under the skin or sprayed into the nose than when swallowed. The response can range from antibodies that cause no symptoms to life-threatening reactions. [14]

Approved peptides can be synthetic too, as ziconotide is. Draft FDA guidance from 2023 asks companies seeking approval for a peptide drug to assess its risk of an immune response, including risk from impurities and clumps of peptide (aggregates). Compounded peptides and products labeled for research get no such FDA review. [15, 6, 37]

Approval does not make a peptide free of risk. Semaglutide’s label opens with a warning printed in a box (a boxed warning), because semaglutide caused a type of thyroid tumor (C-cell tumors) in rodents. Whether it causes them in people is unknown. It must not be used by anyone with a personal or family history of medullary thyroid cancer, or with multiple endocrine neoplasia type 2 (MEN 2), an inherited tumor syndrome. [10, 20]

## Sources

1. U.S. Food and Drug Administration. Definition of the Term “Biological Product”: final rule, 85 FR 10057. 2020. Regulator. Checked 2026-11-13. https://www.federalregister.gov/documents/2020/02/21/2020-03505/definition-of-the-term-biological-product
2. U.S. Food and Drug Administration. Definition of the Term “Biological Product”: proposed rule, 83 FR 63817. 2018. Regulator. Checked 2026-11-13. https://www.federalregister.gov/documents/2018/12/12/2018-26840/definition-of-the-term-biological-product
3. U.S. Food and Drug Administration. 21 CFR 600.3, Definitions, paragraph (h)(6): protein. Electronic Code of Federal Regulations, current to November 10, 2026. Regulator. Checked 2026-11-13. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-F/part-600/subpart-A/section-600.3
4. Al Musaimi O. Exploring FDA-Approved Frontiers: Insights into Natural and Engineered Peptide Analogues in the GLP-1, GIP, GHRH, CCK, ACTH, and α-MSH Realms. Biomolecules. 2024. Reference. Checked 2026-11-13. https://pubmed.ncbi.nlm.nih.gov/38540684/
5. U.S. Food and Drug Administration. Evaluating the Clinical Pharmacology of Peptides; Establishment of a Public Docket; Request for Information and Comments, 86 FR 26525. 2021. Regulator. Checked 2026-11-13. https://www.federalregister.gov/documents/2021/05/14/2021-10179/evaluating-the-clinical-pharmacology-of-peptides-establishment-of-a-public-docket-request-for
6. U.S. Food and Drug Administration. Clinical Pharmacology Considerations for Peptide Drug Products: draft guidance for industry. 2023. Regulator. Checked 2026-11-13. https://www.fda.gov/media/171901/download
7. U.S. Food and Drug Administration. List of Approved NDAs for Biological Products That Were Deemed to be BLAs on March 23, 2020. 2020. Regulator. Checked 2026-11-13. https://www.fda.gov/media/119229/download
8. U.S. Food and Drug Administration. Notice to Compounders: Changes that affect compounding as of March 23, 2020. 2020. Regulator. Checked 2026-11-13. https://www.fda.gov/drugs/human-drug-compounding/notice-compounders-changes-affect-compounding-march-23-2020
9. Wang L et al. Therapeutic peptides: current applications and future directions. Signal Transduct Target Ther. 2022. Reference. Checked 2026-11-13. https://pubmed.ncbi.nlm.nih.gov/35165272/
10. National Library of Medicine, DailyMed. Semaglutide injection, NDA 209637: FDA-approved prescribing information. 2026. Regulator. Checked 2026-11-13. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=adec4fd2-6858-4c99-91d4-531f5f2a2d79
11. Müller TD et al. Glucagon-like peptide 1 (GLP-1). Mol Metab. 2019. Reference. Checked 2026-11-13. https://pubmed.ncbi.nlm.nih.gov/31767182/
12. National Library of Medicine, DailyMed. Glucagon nasal powder, NDA 210134: FDA-approved prescribing information. 2025. Regulator. Checked 2026-11-13. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f1f5df9b-872f-44e5-a18f-f0b68e7e9254
13. National Library of Medicine, DailyMed. Octreotide acetate injection, NDA 019667: FDA-approved prescribing information. 2026. Regulator. Checked 2026-11-13. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4e2c9856-1836-49f0-9472-4dbeeb408f39
14. U.S. Food and Drug Administration. Pharmacy Compounding Advisory Committee, July 23-24, 2026: FDA briefing document for BPC-157-related bulk drug substances. 2026. Regulator. Checked 2026-11-13. https://www.fda.gov/media/193343/download
15. National Library of Medicine, DailyMed. Ziconotide intrathecal infusion, NDA 021060: FDA-approved prescribing information. 2026. Regulator. Checked 2026-11-13. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=57376a5b-4530-9018-e063-6394a90a9afe
16. Buckley ST et al. Transcellular stomach absorption of a derivatized glucagon-like peptide-1 receptor agonist. Sci Transl Med. 2018. Trial in people. Checked 2026-11-13. https://pubmed.ncbi.nlm.nih.gov/30429357/
17. Kim JC et al. Gastrointestinal Permeation Enhancers for the Development of Oral Peptide Pharmaceuticals. Pharmaceuticals (Basel). 2022. Reference. Checked 2026-11-13. https://pubmed.ncbi.nlm.nih.gov/36559036/
18. Drucker DJ. Advances in oral peptide therapeutics. Nat Rev Drug Discov. 2020. Reference. Checked 2026-11-13. https://pubmed.ncbi.nlm.nih.gov/31848464/
19. Lipinski CA et al. Experimental and computational approaches to estimate solubility and permeability in drug discovery and development settings. Adv Drug Deliv Rev. 2001. Reference. Checked 2026-11-13. https://pubmed.ncbi.nlm.nih.gov/11259830/
20. National Library of Medicine, DailyMed. Semaglutide tablets, NDA 213051: FDA-approved prescribing information. 2026. Regulator. Checked 2026-11-13. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=27f15fac-7d98-4114-a2ec-92494a91da98
21. National Library of Medicine, DailyMed. Semaglutide injection and tablets for weight management, NDA 215256 and NDA 218316: FDA-approved prescribing information. 2026. Regulator. Checked 2026-11-13. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ee06186f-2aa3-4990-a760-757579d8f77b
22. U.S. Food and Drug Administration. Drugs@FDA. Orforglipron tablets, NDA 220934: FDA-approved prescribing information. 2026. Regulator. Checked 2026-11-13. https://www.accessdata.fda.gov/drugsatfda_docs/label/2026/220934s003lbl.pdf
23. Shirley M. Orforglipron: First Approval. Drugs. 2026. Reference. Checked 2026-11-13. https://pubmed.ncbi.nlm.nih.gov/42479349/
24. National Library of Medicine, DailyMed. Octreotide delayed-release capsules, NDA 208232: FDA-approved prescribing information. 2025. Regulator. Checked 2026-11-13. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=58d80bc6-bdfb-4908-93e7-aace447c8d1a
25. National Library of Medicine, DailyMed. Linaclotide capsules, NDA 202811: FDA-approved prescribing information. 2026. Regulator. Checked 2026-11-13. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=09beda19-56d6-4a56-afdc-9a77b70b2ef3
26. National Library of Medicine, DailyMed. Cyclosporine capsules and injection, NDA 050625 and NDA 050573: FDA-approved prescribing information. 2026. Regulator. Checked 2026-11-13. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=5e5926a7-1de0-4b54-a5c0-286b6200ff82
27. National Library of Medicine, DailyMed. Cyclosporine capsules and oral solution (modified), NDA 050715 and NDA 050716: FDA-approved prescribing information. 2026. Regulator. Checked 2026-11-13. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=94461af3-11f1-4670-95d4-2965b9538ae3
28. National Library of Medicine, DailyMed. Desmopressin acetate tablets, NDA 019955: FDA-approved prescribing information. 2025. Regulator. Checked 2026-11-13. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6d55baa9-2b62-469c-93ae-3909ab249332
29. National Library of Medicine, DailyMed. Desmopressin acetate nasal spray, ANDA 076703: FDA-approved prescribing information. 2026. Regulator. Checked 2026-11-13. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1ac423b8-27a6-4cef-4a82-c50bf81b4f49
30. American Medical Association, USAN Council. Procedure for USAN name selection. 2025. Reference. Checked 2026-11-13. https://www.ama-assn.org/about/united-states-adopted-names-usan/procedure-usan-name-selection
31. American Medical Association, USAN Council. United States Adopted Names approved stems. 2026. Reference. Checked 2026-11-13. https://www.ama-assn.org/about/united-states-adopted-names-usan/united-states-adopted-names-approved-stems
32. ClinicalTrials.gov. NCT03131687: A Phase 2 Study of Once-Weekly LY3298176 Compared With Placebo and Dulaglutide in Patients With Type 2 Diabetes Mellitus. 2017. Trial in people. Checked 2026-11-13. https://clinicaltrials.gov/study/NCT03131687
33. Sikirić P et al. A new gastric juice peptide, BPC. An overview of the stomach-stress-organoprotection hypothesis and beneficial effects of BPC. J Physiol Paris. 1993. Reference. Checked 2026-11-13. https://pubmed.ncbi.nlm.nih.gov/8298609/
34. Jetté L et al. Human growth hormone-releasing factor (hGRF)1-29-albumin bioconjugates activate the GRF receptor on the anterior pituitary in rats: identification of CJC-1295 as a long-lasting GRF analog. Endocrinology. 2005. Animal study. Checked 2026-11-13. https://pubmed.ncbi.nlm.nih.gov/15817669/
35. U.S. Food and Drug Administration. Pharmacy Compounding Advisory Committee, December 4, 2024: FDA briefing document for CJC-1295-related bulk drug substances. 2024. Regulator. Checked 2026-11-13. https://www.fda.gov/media/183819/download
36. U.S. Food and Drug Administration. Human Drug Compounding. 2026. Regulator. Checked 2026-11-13. https://www.fda.gov/drugs/guidance-compliance-regulatory-information/human-drug-compounding
37. U.S. Food and Drug Administration. FDA’s Concerns with Unapproved GLP-1 Drugs Used for Weight Loss. 2026. Regulator. Checked 2026-11-13. https://www.fda.gov/drugs/drug-alerts-and-statements/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss
38. U.S. Food and Drug Administration. Questions and Answers on Dietary Supplements. 2026. Regulator. Checked 2026-11-13. https://www.fda.gov/food/information-consumers-using-dietary-supplements/questions-and-answers-dietary-supplements
39. U.S. Food and Drug Administration. FDA Authority Over Cosmetics: How Cosmetics Are Not FDA-Approved, but Are FDA-Regulated. 2025. Regulator. Checked 2026-11-13. https://www.fda.gov/cosmetics/cosmetics-laws-regulations/fda-authority-over-cosmetics-how-cosmetics-are-not-fda-approved-are-fda-regulated

## Related articles

- [Which peptides can a pharmacy compound?](https://roverehealth.com/journal/which-peptides-can-be-compounded.md): A pharmacy may compound with a raw peptide only if it meets an official quality standard, is in an FDA-approved drug, or is on an FDA list that names no peptide. Peptides that pass none of these, such as BPC-157, can rely at most on nonbinding FDA or HHS policies of not taking action, which are not approvals.
- [What are GLP-1 medications like semaglutide and tirzepatide?](https://roverehealth.com/journal/glp-1-medications.md): GLP-1 medications mimic a gut hormone that helps control blood sugar and appetite; after large trials, the FDA approved semaglutide and tirzepatide products for type 2 diabetes, weight management and other uses. Digestive side effects are common and weight tends to return after stopping; compounded versions are not FDA-approved and were not tested in those trials.
- [What are BPC-157 and TB-500?](https://roverehealth.com/journal/bpc-157-and-tb-500.md): BPC-157 and TB-500 are lab-made peptides promoted for healing injuries: BPC-157 copies part of a protein reported in stomach juice, and TB-500 copies a fragment of thymosin beta-4, which the body makes. Neither is FDA-approved, and research on healing is almost all in animals, with no completed controlled trial for an injury in people.
- [What does “research use only” mean on a peptide?](https://roverehealth.com/journal/research-use-only-peptides.md): The label is a seller’s statement that a product is for laboratory research, not people: such a product has had no FDA review and is sold without a prescription. The FDA treats research-labeled peptides as unapproved drugs when they are sold for human use, and small lab studies of peptides bought online found wrong amounts and impurities.