What are peptides? Meaning, examples and medicines
Not yet medically reviewed. Fact-checked against the sources listed below on October 7, 2026.How we write and review
Last updated October 7, 2026
A peptide is a short chain of amino acids joined by peptide bonds. The NIH genome institute says peptides typically have 2 to 50 amino acids, while the US FDA treats 40 or fewer as a peptide and more than 40 as a protein. Your body makes peptides such as GLP-1, and more than 80 peptide medicines have been approved.
Key takeaways
- The NIH National Human Genome Research Institute defines a peptide as a short chain of amino acids, typically 2 to 50. For regulation, the US FDA considers 40 or fewer amino acids a peptide and more than 40 a protein.
- Your body makes peptides. Natural GLP-1 is a 37-amino-acid peptide, and glutathione is a tripeptide made of three amino acids.
- Reviews from 2021 and 2022 count more than 80 approved peptide medicines, including the GLP-1 medicines exenatide, liraglutide, dulaglutide and semaglutide.
- Most peptide medicines are injected because digestive enzymes break peptides down. Oral semaglutide is an exception: it is made with an absorption enhancer called SNAC.
- The US FDA says it has warned companies that sold unapproved GLP-1 drugs falsely labelled "for research purposes". In September 2026, FDA Philippines warned against a tirzepatide product labelled "For research only" as an unregistered drug product.
What is a peptide?
A peptide is a short chain of amino acids, the building blocks of proteins, held together by chemical links called peptide bonds. How short "short" is depends on who is defining it.
| Source | How it defines a peptide | Size cutoff |
|---|---|---|
| NIH National Human Genome Research Institute (glossary) | "A short chain of amino acids (typically 2 to 50) linked by chemical bonds (called peptide bonds)." A chain of 51 or more is a polypeptide | About 50, as a general description |
| US National Cancer Institute (dictionary) | "A molecule that contains two or more amino acids." Peptides with many amino acids are called polypeptides or proteins | No upper number given |
| US FDA (21 CFR 600.3 and CDER MAPP 5016.3) | "Any amino acid polymer composed of 40 or fewer amino acids" is a peptide, not a protein. A protein is a chain of more than 40 | 40, as a regulatory definition |
The NIH figure is a general description. The FDA figure is a legal line the US regulator uses to decide how a product is reviewed. FDA quality reviewers split peptide and protein products at this size whether the substance is made chemically, purified from a natural source or made with biotechnology.
What is the difference between a peptide and a protein?
The main difference is size. The NIH genome institute describes a protein as one or more long, folded chains of amino acids, with a sequence set by the DNA of the gene that encodes it.
Where the line falls is partly a matter of definition. In its 2020 final rule on biological products, the US FDA wrote that "there may not be clear scientific consensus" on one number of amino acids that separates the two terms.
Insulin shows how this plays out:
- It has two chains of 21 and 30 amino acids, 51 in total.
- Under its definition, the US FDA counts insulin as a protein, not a peptide.
- Scientific reviews still call insulin the first therapeutic peptide. A 2022 review says insulin was first isolated in 1921 and became the first commercial peptide drug in 1923.
So the same molecule can be called a peptide in a textbook sense and a protein in a US regulatory sense.
What peptides does your body make?
Your body makes many peptides, and several medicines are based on them.
- GLP-1. Natural GLP-1 is a 37-amino-acid peptide that regulates insulin production and release. A 2022 review notes it has a very short half-life in the body.
- Hormones. The same review says therapeutic peptide research began with natural human hormones, including insulin, oxytocin, vasopressin and gonadotropin-releasing hormone (GnRH).
- Glutathione. Glutathione is a tripeptide, made of three amino acids: cysteine, glycine and glutamate. It is made by the body and works as a major antioxidant, according to a 2014 published trial report.
The US Zepbound label describes GLP-1 and GIP as the body's own hormones, and says GLP-1 is a physiological regulator of appetite and calorie intake.
Which peptide medicines are approved?
More than 80 peptide medicines have been approved, according to two reviews. Both counts are as of the review dates, not a current total.
| Review | What it says |
|---|---|
| Muttenthaler et al., Nature Reviews Drug Discovery, 2021 | Since insulin was introduced almost a century earlier, more than 80 peptide drugs have reached the market, for diseases including diabetes, cancer, osteoporosis, multiple sclerosis, HIV infection and chronic pain |
| Wang et al., Signal Transduction and Targeted Therapy, 2022 | More than 80 peptide drugs have been approved worldwide |
Many approved peptide drugs copy natural hormones. Wang et al. give these examples:
| Medicine | Based on | Use named in the review |
|---|---|---|
| Octreotide | Somatostatin (mimic) | Growth hormone producing tumours and pituitary tumours |
| Desmopressin | Vasopressin (mimic) | Diabetes insipidus and nocturia |
| Carbetocin | Oxytocin (homologue) | Not recorded here |
The same review lists GLP-1 receptor agonist peptide drugs approved since 2000 for type 2 diabetes, with their first approval years:
| Medicine | First approval year (Wang et al., 2022) |
|---|---|
| Exenatide | 2005 |
| Liraglutide | 2009 |
| Lixisenatide | 2013 |
| Albiglutide | 2014 |
| Dulaglutide | 2014 |
| Semaglutide | 2017 |
The review does not say which regulator these years refer to. Tirzepatide is not in either review. In the EU, Mounjaro (tirzepatide) was first authorised on 15 September 2022, according to the European Medicines Agency.
The US Ozempic label describes semaglutide as a GLP-1 analogue with 94% sequence homology to human GLP-1. Read more in our guide to GLP-1 medicines.
Why are most peptide medicines injected?
Because the gut breaks peptides down. Wang et al. (2022) say peptides "are easily hydrolyzed by digestive enzymes in the stomach and intestine, and most peptide drugs are thus administrated by injection." They add that peptides tend to be unstable, with a short half-life and fast elimination in the body.
Oral semaglutide is the main exception in the sources for this page:
- Wang et al. cite semaglutide co-formulated with an absorption enhancer called SNAC as approved for oral use in type 2 diabetes. They say SNAC protects semaglutide from being destroyed in the stomach.
- The US label for semaglutide tablets (Rybelsus and Ozempic tablets) says SNAC helps absorption after oral use, and that absorption happens mainly in the stomach.
Even with SNAC, only a small share of each tablet reaches the bloodstream. The US label estimates absolute bioavailability at:
| Product (US label) | Estimated absolute bioavailability |
|---|---|
| Rybelsus | About 0.4% to 1% |
| Ozempic tablets | About 1% to 2% |
How are approved medicines different from "research peptides" sold online?
An approved medicine has been reviewed by a regulator. "Research peptides" are products sold online with labels such as "for research use only" or "not for human consumption", and regulators in the US and the Philippines have acted against them.
What the US FDA says:
- It has warned companies that illegally sold unapproved drugs containing semaglutide, tirzepatide, retatrutide, survodutide or mazdutide that are "falsely labeled 'for research purposes' or 'not for human consumption.'" These were sold directly to consumers for human use with dosing instructions.
- It urges consumers not to purchase these products, "which are of unknown quality and may be harmful to their health."
- Unapproved versions of GLP-1 drugs "do not undergo FDA's review for safety, effectiveness and quality before they are marketed."
- In a 2026 warning letter to an online peptide seller, the FDA said a "for research use only" label did not stop it from treating the products as drugs for human use, because the seller's website showed that intended use. It added that injectable drug products "can pose risks of serious harm to users."
What FDA Philippines says:
- Advisory No. 2026-1309 (dated 17 September 2026) warns against a tirzepatide product labelled "For research only". FDA Philippines treated it as an unregistered drug product with no Certificate of Product Registration.
- Advisory No. 2026-1306 (dated 17 September 2026) warns against an unregistered tirzepatide product sold with a reconstitution solution labelled "Research Use Only".
- Without a Certificate of Product Registration, FDA Philippines says "the public has no assurance as to its quality, safety and efficacy", and use may expose consumers to health risks, including injury or harm.
- No FDA Philippines issuance that defines "research use only" labels was found.
Under RA 9711, the FDA Act of 2009, selling or distributing a health product that requires registration but is not registered with FDA Philippines is prohibited. Our guide on whether peptides are legal in the Philippines covers the law in more detail.
Which peptides does this site cover?
This site has pages on five compounds. Their status differs a lot.
| Compound | What it is | Approval status | Philippine status |
|---|---|---|---|
| Semaglutide | GLP-1 receptor agonist | Approved medicine, as Ozempic, Wegovy and Rybelsus | Ozempic and Wegovy (solution for injection) and Rybelsus (tablets) are listed as registered prescription drugs in the FDA Philippines Verification Portal (checked October 7, 2026) |
| Tirzepatide | Dual GIP and GLP-1 receptor agonist | Approved medicine, as Mounjaro and Zepbound | Mounjaro KwikPen (0.6 mL) and Mounjaro (0.5 mL), solution for injection, are listed as registered prescription drugs in the FDA Philippines Verification Portal (checked October 7, 2026). No record was found for Zepbound. FDA Philippines has warned against several unregistered tirzepatide products in 2026 |
| Retatrutide | A single peptide that acts on the GIP, GLP-1 and glucagon receptors | Investigational, in phase 3 trials. Eli Lilly calls it "an investigational molecule that cannot be legally sold or marketed for human use" | Unverified: no record found in an FDA Philippines Verification Portal search on October 7, 2026. FDA Philippines Advisories No. 2026-1265 and 2026-1392 warn against two unregistered retatrutide products |
| BPC-157 | A synthetic peptide of 15 amino acids, described as derived from gastric proteins | Investigational. Most research is in animals and the lab, with three small human pilot studies | Unverified: no record found in an FDA Philippines Verification Portal search on October 7, 2026. A search of fda.gov.ph for "bpc-157" the same day returned no results |
| Glutathione | A tripeptide antioxidant made by the body | Varies by form | FDA Philippines says injectable glutathione is approved as an adjunct treatment in cisplatin chemotherapy, and that it "has not approved any injectable products for skin lightening" (Advisory No. 2019-182) |
A portal search that finds no record is not an official FDA Philippines statement on a compound, so retatrutide and BPC-157 stay unverified.
How do you check a peptide product in the Philippines?
Use the FDA Philippines Verification Portal. FDA Philippines advisories tell the public to check whether a product is registered at verification.fda.gov.ph, or on its list of verified unregistered health products.
What FDA Philippines says about the portal:
- It was launched on 29 September 2020 and lists FDA-licensed establishments and registered health products, including drugs (Advisory No. 2023-2238).
- A new version with one search box across all FDA databases was announced in Advisory No. 2026-0106, which advises the public to rely solely on it when confirming a product's status.
- It can check both products and FDA-licensed establishments.
- Its information is for verification only and is not regulatory advice.
If you find a product that looks unregistered or counterfeit, FDA Philippines asks the public to report it to ereport@fda.gov.ph or through e-Sumbong on www.fda.gov.ph.
Frequently asked questions
What are peptides?
Peptides are short chains of amino acids linked by peptide bonds. The NIH National Human Genome Research Institute says a peptide typically has 2 to 50 amino acids, and calls a longer chain of 51 or more a polypeptide. The US National Cancer Institute defines a peptide as a molecule with two or more amino acids.
What is the difference between a peptide and a protein?
Size. The NIH genome institute describes a protein as one or more long, folded chains of amino acids. For regulation, the US FDA treats a chain of 40 or fewer amino acids as a peptide and more than 40 as a protein. The FDA has also said there may be no clear scientific agreement on one exact number.
How many amino acids are in a peptide?
It depends on the definition. The NIH genome institute says typically 2 to 50. The US FDA uses 40 or fewer for regulatory purposes, and the US National Cancer Institute says two or more, with longer chains called polypeptides or proteins.
Is insulin a peptide or a protein?
It depends on who is counting. Insulin has two chains of 21 and 30 amino acids, 51 in total, so the US FDA counts it as a protein under its definition. Scientific reviews call insulin the first therapeutic peptide drug.
What are examples of peptides in the body?
Natural GLP-1 is a 37-amino-acid peptide that helps regulate insulin production and release. A 2022 review names insulin, oxytocin, vasopressin and gonadotropin-releasing hormone (GnRH) as natural human hormones that therapeutic peptide research started from. Glutathione, made by the body, is a tripeptide.
How many peptide medicines are approved?
A 2021 review in Nature Reviews Drug Discovery says more than 80 peptide drugs have reached the market, and a 2022 review says more than 80 have been approved worldwide. These counts are as of those review dates, not a current total.
Is semaglutide a peptide?
Yes. A 2022 review lists semaglutide among the GLP-1 receptor agonist peptide drugs, with a first approval year of 2017. The US Ozempic label describes it as a GLP-1 analogue with 94% sequence homology to human GLP-1.
Why are most peptide medicines injected?
A 2022 review says peptides are easily broken down by digestive enzymes in the stomach and intestine, so most peptide drugs are given by injection. The same review says peptides tend to have a short half-life and are cleared from the body quickly.
Can peptides be taken as tablets?
Some can. Oral semaglutide is made with an absorption enhancer called SNAC, which the US label says helps absorption, mainly in the stomach. The label estimates that only about 0.4% to 2% of an oral dose reaches the bloodstream, depending on the tablet product.
What are research peptides?
These are products sold online with labels such as "for research use only" or "not for human consumption". The US FDA says it has warned companies that sold unapproved semaglutide, tirzepatide, retatrutide, survodutide or mazdutide falsely labelled this way, directly to consumers with dosing instructions, and urges consumers not to purchase them.
What are the risks of peptides sold online?
FDA Philippines says that without a Certificate of Product Registration the public has "no assurance as to its quality, safety and efficacy", and that use may expose consumers to health risks, including injury or harm. The US FDA says unapproved GLP-1 products "do not undergo FDA's review for safety, effectiveness and quality before they are marketed."
How do I check if a peptide product is registered in the Philippines?
FDA Philippines tells the public to search its Verification Portal at verification.fda.gov.ph, or its list of verified unregistered health products. FDA Philippines says the portal can also check whether an establishment is FDA-licensed. Suspected unregistered or counterfeit products can be reported to ereport@fda.gov.ph or through e-Sumbong.
Sources
- Peptide, Talking Glossary of Genomic and Genetic Terms, NIH National Human Genome Research Institute
- Protein, Talking Glossary of Genomic and Genetic Terms, NIH National Human Genome Research Institute
- Peptide, NCI Dictionary of Cancer Terms, US National Cancer Institute
- 21 CFR 600.3, Definitions (protein), US Code of Federal Regulations
- CDER MAPP 5016.3 Rev. 1, US FDA
- Definition of the Term "Biological Product", final rule, US FDA, Federal Register, 2020
- Muttenthaler et al., Trends in peptide drug discovery, Nature Reviews Drug Discovery, 2021 (PMID 33536635)
- Wang et al., Therapeutic peptides, Signal Transduction and Targeted Therapy, 2022 (PMC8844085)
- Ozempic (semaglutide) injection, US prescribing information, DailyMed
- Rybelsus and Ozempic (semaglutide) tablets, US prescribing information, DailyMed
- Zepbound (tirzepatide), US prescribing information, DailyMed
- Mounjaro, European public assessment report, European Medicines Agency
- Watanabe et al., topical glutathione trial, Clin Cosmet Investig Dermatol, 2014 (PMID 25378941)
- FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss, US FDA
- US FDA warning letter to an online peptide seller, August 2026
- FDA Advisory No. 2026-1309, FDA Philippines
- FDA Advisory No. 2026-1306, FDA Philippines
- FDA Advisory No. 2026-1265, FDA Philippines
- FDA Advisory No. 2026-1392, FDA Philippines
- FDA Advisory No. 2019-182, glutathione as a skin lightening agent, FDA Philippines
- FDA highlights the FDA Verification Portal, FDA Philippines, 2026
- FDA Advisory No. 2023-2238, Utilization of the FDA Verification Portal, FDA Philippines
- FDA Advisory No. 2026-0106, Launch of the new FDA Verification Portal, FDA Philippines
- Republic Act No. 9711, Food and Drug Administration Act of 2009, Lawphil
- FDA Philippines Verification Portal, search for semaglutide, October 7, 2026
- FDA Philippines Verification Portal, search for tirzepatide, October 7, 2026
- FDA Philippines Verification Portal, search for Zepbound, October 7, 2026
- FDA Philippines Verification Portal, search for retatrutide, October 7, 2026
- FDA Philippines Verification Portal, search for BPC-157, October 7, 2026
- Lilly retatrutide phase 3 results, Eli Lilly press release, September 29, 2026
- Rosenstock et al., phase 2 retatrutide type 2 diabetes trial, Lancet, 2023 (PMID 37385280)
- McGuire et al., narrative review of BPC-157 for musculoskeletal healing, 2025 (PMID 40789979)
- Yuan et al., review of BPC-157 in tissue repair and pain, 2026 (PMID 41898733)
- Search of fda.gov.ph for "bpc-157", FDA Philippines, October 7, 2026
Related reading
This content is for education only and is not medical advice. Talk to a licensed doctor before starting any treatment.