# What Are Peptides? What They Do in the Body, and Which Are Actual Drugs

By Ruth Calder, Enforcement Editor (https://glpwatchdog.org/authors/ruth-calder) | Published: 2026-11-04

Canonical page: https://glpwatchdog.org/research/what-are-peptides

> Peptides are short chains of amino acids, typically 2 to 50, that the body uses as hormones and signals. More than 80 had reached the market as drugs by 2021, including semaglutide. Others sold online are in no approved drug, and the word alone says nothing about safety.

## Key points

- Peptides are short chains of amino acids, typically 2 to 50, joined by peptide bonds.
- In the body they act as hormones, growth factors and neurotransmitters, usually by binding receptors on cells.
- More than 80 peptide drugs had reached the market by 2021; semaglutide and tirzepatide are built on peptides.
- Most peptide drugs are injected because peptides break down quickly; only 0.4% to 1% of a Rybelsus dose reaches the blood.
- Peptides such as BPC-157 and TB-500 are not components of any FDA-approved drug, and HHS's October 2026 policy is not an approval.

Peptides are short chains of amino acids, typically 2 to 50, joined by chemical links called peptide bonds.[1] Your body makes them as hormones and signals; insulin and oxytocin are the classic examples.[5] More than 80 had reached the market as drugs by 2021,[6] and semaglutide, the drug inside Ozempic and Wegovy, is one of the best known.[9] **The word covers very different things, though.** Many peptides sold online have no FDA approval for any use, and being a peptide says nothing about whether a product works or is safe.[17][18]

> **About this article.** This page explains the molecule and the categories it falls into. For the clinic treatment, see [what is peptide therapy](https://glpwatchdog.org/research/what-is-peptide-therapy). For individual products, use our [peptide directory](https://glpwatchdog.org/peptides). Nothing here is a dose, a protocol or a recommendation to use any peptide.

## What are peptides, in simple terms?

Think of amino acids as beads. There are 20 standard kinds, and the body can make some of them while others must come from food.[2] String a few beads together and you have a peptide. String hundreds or thousands together and fold the result, and you have a protein.[3] The order of the beads decides what the chain does, which is why two peptides of similar length can have nothing in common.

*Amino acid, peptide or protein: the difference is mostly size*

|   | Size | Example |
| --- | --- | --- |
| Amino acid | One unit; 20 standard kinds[2] | Tryptophan, leucine |
| Peptide | Typically 2 to 50 amino acids[1] | Glutathione (3),[15] oxytocin (9)[7] |
| Protein | Hundreds or thousands of amino acids in most cases[3] | Most of the working molecules in a cell[3] |

The boundary is a convention. The National Human Genome Research Institute puts it at about 50 amino acids.[1] US drug regulation uses 40: any defined chain longer than that counts as a protein.[4] So insulin, with 51 amino acids, is often called a peptide by scientists[5] and sits on the protein side of FDA’s line. Tesamorelin, at 44,[11] was moved to a biologics license for the same reason.[20] The chemistry of the GLP-1 drugs is laid out in [are GLP-1 drugs peptides?](https://glpwatchdog.org/research/are-glp1-drugs-peptides)

## What do peptides do in the body?

Mostly, they carry messages. Natural peptides act as hormones, growth factors and neurotransmitters, and some defend against infection.[5] A peptide usually works by fitting a receptor on the outside of a cell and switching it on or off, since peptides generally cannot cross the cell membrane.[5] A few familiar examples:

- **Oxytocin**, nine amino acids, is released from the pituitary and is given by injection in hospitals during labor.[7]
- **Insulin** regulates blood glucose.[5]
- **GLP-1** is a gut hormone that affects blood sugar and body weight. The natural version lasts only minutes in the blood.[8]
- **Growth hormone-releasing hormone** is made in the hypothalamus and tells the pituitary to release growth hormone.[11]
- **Glutathione**, three amino acids, is a central antioxidant in cells.[15]

Peptides also come from food. Proteins contain shorter active sequences that can be released during digestion or processing.[14] Researchers have identified many in the lab, but a review of the field points to poor survival in the gut, variable absorption and a lack of well-designed clinical trials as the obstacles to health claims.[14]

## What are the main types of peptides?

Scientists sort peptides by origin and function. For anyone reading a label or a clinic menu, the more useful split is by what kind of product it is, because that decides who checked it and what evidence exists.

*Kinds of peptide you will come across, November 2026*

| Kind | Examples | Who oversees it | Human evidence |
| --- | --- | --- | --- |
| Made by your body | Insulin, oxytocin, GLP-1 | Not applicable | Basic physiology |
| Approved drugs | Semaglutide, tirzepatide, setmelanotide, bremelanotide, tesamorelin | FDA reviews trials before approval | Trials for the labeled use |
| Dietary | Collagen peptides, peptides in food | Sold as food or supplements; FDA does not approve supplements before sale[16] | Varies; often small trials |
| Cosmetic | Skin-cream peptides such as copper tripeptide | Sold as cosmetics | Small trials |
| Compounded | Sermorelin; six peptides under the 2026 HHS policy | State-licensed pharmacy; not FDA-approved[17] | Often thin |
| Research-use-only | Vials sold as not for human use | No regulator checks the batch before sale | None for the product itself |

## Which peptides are actual drugs?

Plenty. By a 2021 count, more than 80 peptide drugs had reached the market for diabetes, cancer, osteoporosis, multiple sclerosis, HIV infection and chronic pain.[6] Early ones copied human hormones. Newer ones change the sequence so the drug lasts longer or binds better.

*Examples of FDA-approved peptide drugs, from their current labels*

| Drug | What it is | Approved for (in brief) |
| --- | --- | --- |
| Pitocin (oxytocin) | A nonapeptide, nine amino acids[7] | Obstetric uses in hospital |
| Vyleesi (bremelanotide) | A cyclic heptapeptide, seven amino acids[13] | One form of low sexual desire in premenopausal women |
| Imcivree (setmelanotide) | A cyclic peptide of eight amino acids[12] | Rare genetic and acquired forms of obesity |
| Ozempic, Wegovy, Rybelsus (semaglutide) | A modified GLP-1 peptide[9] | Type 2 diabetes; weight management (Wegovy) |
| Zepbound, Mounjaro (tirzepatide) | A peptide based on the GIP hormone sequence[10] | Weight management (Zepbound); type 2 diabetes (Mounjaro) |
| Egrifta WR (tesamorelin) | 44 amino acids plus a small chemical group[11] | Excess abdominal fat in adults with HIV and lipodystrophy |

An approval covers the use that was tested, nothing more. Tesamorelin is a good example: its label limits it to one kind of abdominal fat in adults with HIV.[11] The fuller list, with each label, is in [FDA-approved peptides](https://glpwatchdog.org/research/fda-approved-peptides).

## Why are most peptide drugs injected?

Two weaknesses explain it. Peptides are unstable in the body and cross membranes poorly,[5] and a swallowed peptide faces the same digestion as any other protein in a meal.[14] Natural GLP-1 shows how short-lived these molecules can be: its half-life is about 1.5 minutes after an IV dose.[8] Drug makers changed the chain and added a fatty side group so that semaglutide lasts about a week.[9]

Getting one through the gut takes real engineering. Semaglutide tablets contain an absorption enhancer called SNAC and have to be swallowed fasting with a little water, and even then only about 0.4% to 1% of a Rybelsus dose reaches the blood.[9] This is why a claim that a peptide works as a capsule or a spray needs its own evidence.

## Are all peptides sold today approved or tested?

No, and this is where the word causes the most confusion. Popular names such as BPC-157, TB-500, MOTS-c and Epitalon are not components of any FDA-approved drug,[17] and most have little human data. Our count of [which peptides on the menu have human trials](https://glpwatchdog.org/research/the-peptide-menu-what-has-human-trials) shows how uneven the record is. A 2026 sports-medicine review describes a gray market operating largely outside regulatory oversight, where rigorous human safety data are scarce.[19] On BPC-157, FDA says the agency lacks the information to know whether it would cause harm in people.[18]

On October 28, 2026, HHS said it does not intend to take enforcement action against 503A pharmacies that compound six peptides (BPC-157, TB-500, Epitalon, Semax, KPV and MOTS-c) when strict conditions are met.[17] That is an interim enforcement position, and the Federal Register notice of October 30 calls it a draft, with two weeks for written comments.[21] The policy itself says compounded drugs are not FDA-approved, and it gives research-use-only products as the risk it wants to discourage.[17] For specifics, see [are peptides safe?](https://glpwatchdog.org/research/are-peptides-safe) and [are peptides legal?](https://glpwatchdog.org/research/are-peptides-legal), or look up any name in the [peptide status checker](https://glpwatchdog.org/tools/peptide-status-checker).

One more mix-up comes from gyms: peptides are not steroids. They differ in chemistry and in US law. And NAD+, often sold beside them, is not a peptide at all, because it is built from nucleotides.

## Frequently asked questions

### What are peptides?

Peptides are short chains of amino acids, typically 2 to 50, joined by peptide bonds. The body uses them as hormones and signaling molecules. Some are also made into approved drugs, and others are sold in supplements, skin creams and unapproved injections.

### What do peptides do?

Most peptides carry messages between cells. They act as hormones, growth factors and neurotransmitters by binding to receptors. Insulin, oxytocin and GLP-1 are well-known examples. What a given peptide does depends on its amino acid sequence.

### What is the difference between peptides and proteins?

Size. Both are chains of amino acids, but a peptide is short and a protein is long and folded. Scientists often put the line near 50 amino acids, and US drug rules define a protein as a chain of more than 40.

### Are peptides natural?

Your body makes many peptides, and food contains them. Many sold as drugs or supplements are synthetic or altered versions. A natural origin does not show that a product is safe or that it works.

### Are peptides steroids?

No. Peptides are chains of amino acids, and anabolic steroids are smaller molecules related to testosterone. They are regulated differently in the US as well.

### Are peptides safe?

It depends on the product. FDA-approved peptide drugs have known, labeled risks. Compounded peptides are not FDA-approved, and research-use-only vials have no oversight. For many peptides sold online, human safety data are scarce.

## References

1. National Human Genome Research Institute Peptide, Talking Glossary of Genomic and Genetic Terms. NIH. 2026. https://www.genome.gov/genetics-glossary/Peptide
2. National Human Genome Research Institute Amino Acids, Talking Glossary of Genomic and Genetic Terms. NIH. 2026. https://www.genome.gov/genetics-glossary/Amino-Acids
3. MedlinePlus Genetics, National Library of Medicine What are proteins and what do they do?. MedlinePlus. 2026. https://medlineplus.gov/genetics/understanding/howgeneswork/protein/
4. Code of Federal Regulations 21 CFR 600.3, Definitions (paragraph (h)(6), protein). Legal Information Institute. 2026. https://www.law.cornell.edu/cfr/text/21/600.3
5. Wang L, Wang N, Zhang W, Cheng X, et al. Therapeutic peptides: current applications and future directions. Signal Transduction and Targeted Therapy. 2022. PMID: 35165272. DOI: 10.1038/s41392-022-00904-4. https://pubmed.ncbi.nlm.nih.gov/35165272/
6. Muttenthaler M, King GF, Adams DJ, Alewood PF. Trends in peptide drug discovery. Nature Reviews Drug Discovery. 2021. PMID: 33536635. DOI: 10.1038/s41573-020-00135-8. https://pubmed.ncbi.nlm.nih.gov/33536635/
7. Par Health USA PITOCIN (oxytocin) injection, prescribing information. DailyMed. 2026. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6e5a66fc-e507-497c-b5ce-44a8c95898ad
8. Knudsen LB, Lau J. The Discovery and Development of Liraglutide and Semaglutide. Frontiers in Endocrinology. 2019. PMID: 31031702. DOI: 10.3389/fendo.2019.00155. https://pubmed.ncbi.nlm.nih.gov/31031702/
9. Novo Nordisk RYBELSUS and OZEMPIC (semaglutide) tablets, prescribing information. DailyMed. 2026. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=27f15fac-7d98-4114-a2ec-92494a91da98
10. Eli Lilly and Company ZEPBOUND (tirzepatide) injection, prescribing information. DailyMed. 2026. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=487cd7e7-434c-4925-99fa-aa80b1cc776b
11. Theratechnologies Inc. EGRIFTA WR (tesamorelin) for injection, prescribing information. DailyMed. 2026. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=839334d3-8c1d-4c26-9036-2ab524a6ea75
12. Rhythm Pharmaceuticals IMCIVREE (setmelanotide) injection, prescribing information. DailyMed. 2026. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=70c3ccf7-4df0-4c75-ba07-fede9970c8d9
13. Cosette Pharmaceuticals VYLEESI (bremelanotide injection), prescribing information. DailyMed. 2025. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f1d0c1b5-2f39-4bad-a6a4-0066e3ad5dcf
14. Chakrabarti S, Guha S, Majumder K. Food-Derived Bioactive Peptides in Human Health: Challenges and Opportunities. Nutrients. 2018. PMID: 30424533. DOI: 10.3390/nu10111738. https://pubmed.ncbi.nlm.nih.gov/30424533/
15. Lapenna D. Glutathione and glutathione-dependent enzymes: From biochemistry to gerontology and successful aging. Ageing Research Reviews. 2023. PMID: 37683986. DOI: 10.1016/j.arr.2023.102066. https://pubmed.ncbi.nlm.nih.gov/37683986/
16. U.S. Food and Drug Administration Questions and Answers on Dietary Supplements. FDA. 2026. https://www.fda.gov/food/information-consumers-using-dietary-supplements/questions-and-answers-dietary-supplements
17. U.S. Department of Health and Human Services HHS Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances (with Appendix A and Appendix B). HHS. 2026. https://www.hhs.gov/sites/default/files/hhs-503a-peptide-enforcement-discretion-policy-appendix-b.pdf
18. U.S. Food and Drug Administration Certain bulk drug substances for use in compounding that may present significant safety risks. FDA. 2026. https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
19. Mendias CL, Awan TM. Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance. Sports Medicine. 2026. PMID: 41966639. DOI: 10.1007/s40279-026-02437-0. https://pubmed.ncbi.nlm.nih.gov/41966639/
20. U.S. Food and Drug Administration List of Approved NDAs for Biological Products That Were Deemed to be BLAs on March 23, 2020. FDA. 2020. https://www.fda.gov/media/119229/download
21. U.S. Department of Health and Human Services Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances (notice of availability, 91 FR 68526, document 2026-22192). Federal Register. 2026. https://www.federalregister.gov/documents/2026/10/30/2026-22192/enforcement-discretion-policy-regarding-503a-compounding-using-certain-peptide-bulk-drug-substances

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Cite as: GLP Watchdog, Ruth Calder, "What Are Peptides? What They Do in the Body, and Which Are Actual Drugs", published 2026-11-04. https://glpwatchdog.org/research/what-are-peptides

Canonical HTML page: https://glpwatchdog.org/research/what-are-peptides

Medical disclaimer: Nothing here is medical advice. We report on this subject; we do not treat anyone. Whether to begin a medication, supplement, or treatment, whether to adjust it, and whether to stop are questions for a clinician licensed to answer them, who knows your history.