Types of peptides

How are peptides divided by function?

The functions of peptides in the body and as drugs are very diverse. The review by Wang and colleagues describes how peptide drug research began with natural hormones such as insulin, oxytocin, vasopressin, and GnRH, and then expanded with hormone mimetics, peptides obtained from nature (for example from animal venoms), and peptides designed in the laboratory. ^[1] The groups below are used to organize this site’s guides; one substance can fall into more than one group.

Hormone and incretin peptides

Insulin and GLP-1 are the best-known examples of this group. GLP-1 is one of the “incretin” hormones released from the gut that increase insulin secretion after a meal. According to Wang and colleagues, the half-life of GLP-1 in the body is very short, and longer-lasting drugs (dulaglutide, liraglutide, semaglutide) were developed by modifying its sequence. ^[1] The same review lists octreotide as a somatostatin mimetic and desmopressin as a vasopressin mimetic peptide drug. ^[1] Tirzepatide stimulates the GIP and GLP-1 receptors, and retatrutide, which is at the research stage, additionally stimulates the glucagon receptor; details are in the What is GLP-1? and GLP-1 agonists guides.

Growth hormone axis: secretagogues

These peptides are not growth hormone itself; they stimulate the release of growth hormone from the pituitary. WADA’s 2026 list, under the heading S2.2.4 “growth hormone-releasing factors,” names CJC-1295 among growth hormone-releasing hormone (GHRH) analogs and ipamorelin among growth hormone secretagogues and mimetics; section S2 is prohibited at all times. ^[4] According to the FDA’s assessment, ipamorelin acetate may carry a risk of immune response by some routes of administration because of aggregation and impurities; the FDA also writes that serious adverse events, including death, were reported in a published study in which it was given intravenously. ^[5] The abstract of the randomized study that the FDA links to on this line, however, does not mention death and reports any adverse event more often in the placebo group (94.8% versus 87.5%). ^[10] All of the evidence is in the CJC-1295 and Ipamorelin guides.

Peptides with tissue-repair claims

BPC-157 and TB-500 are sold online with claims of wound, tendon, and muscle healing. WADA’s 2026 list names BPC-157 in S0 (substances not approved for therapeutic use in humans by any governmental health authority) and “thymosin-β4 and its derivatives, e.g., TB-500” in section S2.3. ^[4] For both substances, the findings come mostly from animal and cell studies; details are in the BPC-157 and TB-500 guides.

Cosmetic and signal peptides

Peptides used in skin-care products belong to this group. CosIng, the EU’s cosmetic ingredient database, registers Copper Tripeptide-1 (GHK-Cu) as a copper complex of a tripeptide with the function “skin conditioning.” ^[8] Palmitoyl Pentapeptide-4 is registered in the same database as the reaction product of palmitic acid with a pentapeptide, with the function “skin conditioning — miscellaneous.” ^[9] This registration is not an approval of efficacy; it shows the function with which the ingredient is used in cosmetics. The evidence is evaluated in the GHK-Cu and GHK-Cu serums and creams guides.

Peptides acting on the nervous system (neuropeptides)

Selank and semax, sold online as “nootropics,” are seven-amino-acid synthetic peptides developed in Russia; semax is an analog of a fragment of the hormone ACTH, while selank is classified as an anxiolytic. The evidence is limited to small, mostly placebo-free studies published in Russian; details are in the Selank / Semax guide.

Antimicrobial peptides

According to the review by Mookherjee and colleagues, host defence peptides (antimicrobial peptides) are naturally occurring peptides that fight infection by directly killing microbes and/or influencing the immune response; work to develop treatments for infection, chronic inflammation, and wound healing is ongoing. ^[2] From this group, the cathelicidin LL-37 is one of the peptides nominated to the FDA for compounding drugs in pharmacies in the US; on the FDA’s list, LL-37 is among the substances that were previously in the significant safety risk category, whose nomination was withdrawn, and whose safety assessment remains on the page. ^[5]

Peptides of mitochondrial origin

Lee and colleagues reported in 2015 that they found a short open reading frame within the 12S rRNA gene in mitochondrial DNA and that it encodes the 16-amino-acid peptide MOTS-c; in mice, MOTS-c prevented age-dependent and high-fat-diet-induced insulin resistance and diet-induced weight gain. ^[3] These findings are mouse data. WADA’s 2026 list names MOTS-c in section S4.4.1 among AMPK activators. ^[4] Details are in the MOTS-c guide. Epitalon, a four-amino-acid peptide sold with anti-aging claims, was synthesized based on bovine pineal extract; telomere claims rest on cell and mouse data.

How are peptides divided by legal status?

This distinction best describes how much is known about a peptide. In a licensed drug, efficacy and safety have been evaluated in clinical trials, manufacturing quality is inspected, and side effects are written in the product information. In an unlicensed product, none of these steps is assured.

The substances in the licensed row are on TİTCK’s (Turkish Medicines and Medical Devices Agency) Licensed Human Medicinal Products List dated October 16, 2026; the same list contains no product with BPC-157, TB-500, CJC-1295, ipamorelin, epitalon, MOTS-c, selank, semax, or retatrutide as an active substance. ^[6] The legal consequences are in the Are peptides legal? guide, and the meaning of labels is in the What is a research peptide? guide.

By which routes are peptides given?

The route of administration relates to how the peptide is protected from digestion and rapid breakdown. According to Wang and colleagues, because peptides are easily broken down by digestive enzymes in the stomach and gut, most peptide drugs are given by injection; for the oral route, routes such as absorption enhancers, inhalation, transdermal delivery, and implantable pumps are being investigated. ^[1] The information below describes the forms of licensed products; it is not usage instructions.

• Subcutaneous injection: GLP-1 receptor agonists, tirzepatide, insulins, and teriparatide are licensed in pen or vial form on the TİTCK list. ^[6] According to Wang and colleagues, structural modifications that extend half-life in drugs such as dulaglutide have allowed once-weekly injection. ^[1] The meaning of half-life is in the What does half-life mean? guide.
• Intramuscular / intravenous: Oxytocin appears on the TİTCK list as ampoules used intramuscularly and intravenously. ^[6]
• Oral route: The semaglutide tablet is formulated with an absorption-enhancing excipient (salcaprozate sodium); according to the EMA, absorption occurs mainly in the stomach, bioavailability is about 1–2%, and absorption is highly variable from person to person. ^[7]
• Nasal route: Desmopressin is a peptide drug licensed on the TİTCK list in nasal spray form. ^[6]
• Subcutaneous implant: Leuprorelin (leuprolide), a peptide derived from GnRH ^[1], is licensed on the TİTCK list in implant and subcutaneous injection forms. ^[6]
• Applied to the skin: Cosmetic peptides are used in creams and serums; CosIng entries describe the skin-care function. ^[8]

The routes used for unlicensed research peptides (injection, nasal spray, capsule) have not undergone assessment by any authority; absorption, stability, and sterility information for these products is not verified. The sensitivity of peptides to heat and light is covered in the How are peptides stored? guide.

Which class are the peptides on the site in?

The WADA column shows only whether it is named on the list. ^[4] The S0 section of the list covers every substance not listed in other sections and not approved for therapeutic use in humans by any governmental health authority; a substance not named is therefore not automatically permitted. ^[4]

Where to go after this guide?

The chemistry and history of peptides are in What are peptides?, the risks in Peptide side effects, and the label language of unlicensed products in What is a research peptide?. This guide does not recommend personal products, sources, or doses.