Why study naturally occurring peptides

Researchers study naturally occurring peptides because the body has already tested them. A native peptide has a receptor it binds, a tissue that makes it and a job it does, so a researcher starts with a known signal and a known target. Insulin, the first peptide therapeutic, entered medical practice in the 1920s, and a 2018 review from the Ferring Research Institute describes peptide drug discovery as built on "endogenous human peptides" before it widened to other natural sources and designed sequences. ^[2]

The numbers show how far that approach has run. Muttenthaler and colleagues counted more than 80 peptide drugs on the market in 2021, and traced the field from early work on human hormones through rational design and "peptide drugs derived from nature". ^[1] A 2022 review in Signal Transduction and Targeted Therapy says new chemistry and delivery methods "have helped to overcome the inherent drawbacks of peptides", and that "a wide variety of natural and modified peptides" have been obtained and studied. ^[10]

Nature supplies the sequence. Chemistry decides whether that sequence survives long enough to study.

Natural peptides are chains of amino acids that the body, or another organism, makes for itself. Some are hormones, some are fragments cut from larger proteins, and some come from unexpected places such as mitochondrial DNA. The table sets out examples we checked against PubChem and PubMed on 29 September 2026, including four compounds in our catalogue.

GHK is the clearest case of a natural peptide becoming a research compound. Pickart's group isolated the plasma tripeptide and found it co-isolated with roughly equimolar copper; in 1980 they reported that it readily forms complexes with copper(II) and increased copper uptake into cultured hepatoma cells. ^[14] GHK-Cu is that copper complex, and our GHK-Cu research overview covers the structure and the cell and animal literature in detail.

Thymosin alpha-1 is subtler. Goldstein's team sequenced a 28-residue peptide from calf thymus in 1977. ^[16] Seven years later, Haritos and colleagues found that rat thymus holds a roughly 112-residue protein, prothymosin alpha, with the thymosin alpha-1 sequence at its start, and proposed that thymosin alpha-1 is generated from it during isolation. ^[19] The thymosin alpha-1 research overview sets out the full history.

Natural peptides come from three main routes: the body's own genes, larger precursor proteins that are cut into pieces, and food proteins broken down during digestion.

1. Cut from a precursor. GLP-1 is produced in intestinal L-cells "by differential processing of proglucagon". ^[4] Thymosin alpha-1 sits at the start of prothymosin alpha. ^[19]
2. Made by cell enzymes. Glutathione is described as the most abundant low molecular weight thiol compound synthesised in cells. ^[13]
3. Encoded in mitochondria. MOTS-c comes from a short open reading frame within the mitochondrial 12S rRNA gene, reported in Cell Metabolism in 2015. ^[18]
4. Released from food. A 2025 systematic review lists milk, fish and plants as sources of dietary peptides, and found eight randomised trials from 2019 to 2024 that met its criteria. ^[20]

Food peptides are mixtures. A hydrolysed milk or collagen protein holds many sequences at once, in amounts that vary by batch and process. A research compound is one defined sequence, so the two answer different laboratory questions.

Many peptide medicines are modified because native peptides tend to be broken down fast. GLP-1 shows the problem. Holst's 2007 review states that GLP-1 "is extremely rapidly metabolized and inactivated by the enzyme dipeptidyl peptidase IV even before the hormone has left the gut". ^[4] In a 1995 study of intravenously infused GLP-1 in healthy adults and adults with type 2 diabetes, intact GLP-1 made up only 19.9% to 25.0% of the measured increase; the rest was a truncated metabolite. ^[21]

Novo Nordisk's answer was semaglutide. Its discovery paper describes two amino acid substitutions against human GLP-1 (Aib at position 8 and Arg at position 34) and a fatty acid attached at lysine 26 to raise albumin binding. The plasma half-life was 46.1 hours in mini-pigs. ^[5] The sequence is still recognisably GLP-1. The chemistry keeps it in circulation.

The TGA's own list of approved peptide-based medicines shows the same pattern. It names insulin and insulin analogues, GLP-1 receptor agonists such as semaglutide, oxytocin, vasopressin analogues such as desmopressin, and somatostatin analogues such as octreotide. ^[12] Two entries are native hormones. The rest are analogues of a native hormone.

Retatrutide sits further along that line. Eli Lilly scientists describe LY3437943 as a single peptide with agonist activity at the glucagon, GIP and GLP-1 receptors, and every author declared employment with Lilly. ^[22] PubChem's structure for retatrutide shows 2-methylpropanoyl (Aib) residues and a C20 fatty diacid chain. ^[6] It is a designed molecule inspired by gut hormones. Calling it a natural peptide misdescribes it.

A synthetic peptide is the same molecule as the natural one when its sequence and its modifications match exactly. The chemistry that makes this possible is solid-phase peptide synthesis, which Bruce Merrifield developed at Rockefeller University; he wrote that it made large numbers of analogues practical for structure-function studies on hormones and growth factors. ^[23]

Synthesis also creates the risk. A 2014 review from Ghent University, which states that most peptides today are made by solid-phase synthesis, lists the impurities it produces: deleted or inserted amino acids, racemised residues, leftover protecting groups, oxidised side chains, trifluoroacetate counter-ions and even unrelated peptides from poor manufacturing practice. ^[3] The authors warn that these impurities can mislead early functionality studies and lead to "erroneous conclusions". ^[3]

So "natural" describes the sequence on paper. What sits in the vial is a separate question, and only a test answers it. Every batch we sell is tested by an independent lab before it goes on sale: purity by HPLC and identity by mass spectrometry. The certificate is published under the batch number printed on the vial, and you can search it in our certificate of analysis library. Our guide on how to read a peptide certificate of analysis shows how to match the measured mass against the published value, for example 340.38 g/mol for GHK or 402.92 g/mol for the copper complex. ^[15][24]

The claims that circulate about natural peptides mix accurate trial figures with statements no study supports. We checked the ones most often repeated against primary sources on 29 September 2026.

KPV, a fragment of the natural hormone alpha-MSH, has the thinnest human record of the four blend compounds. We found no clinical trial of KPV. Our KPV 10mg vial is sold for laboratory research, with its batch certificate in the library.

The TGA has published the adverse events it has received for unapproved peptide products, and they include serious reactions. Its list names severe allergic reactions needing adrenaline and hospital care, systemic inflammatory response syndrome, generalised hypersensitivity symptoms, insomnia, blurred vision, extreme tiredness, joint pain, musculoskeletal injuries such as Achilles tendinitis, and poor product quality. ^[31] The same page names BPC-157, GHK-Cu, TB-500, retatrutide and CJC-1295 as examples of unapproved peptide products. ^[31]

Controlled trials give a narrower picture for specific compounds in specific populations:

• Retatrutide, phase 2 obesity trial: the most common adverse events were gastrointestinal, mostly mild to moderate and more frequent in the higher-strength groups; heart rate rose and peaked at 24 weeks. ^[25]
• Thymosin alpha-1, TESTS trial: in 1,106 adults with sepsis across 22 Chinese centres, 28-day mortality was 23.4% against 24.1% with placebo, and no secondary or safety outcome differed significantly. ^[32]
• BPC-157: the 2025 systematic review found no clinical safety data. ^[28]

A natural sequence carries no guarantee about the product in a vial. Contamination, wrong content and sterility sit with manufacturing, which the TGA lists among the unknowns for unapproved products. ^[31]

A peptide's legal status in Australia depends on its own entry in the Poisons Standard, and origin plays no part. The June 2026 instrument, which commenced on 1 June 2026, lists oxytocin, insulins and glutathione for parenteral use in Schedule 4 (prescription only), and all three are natural molecules. ^[9] BPC-157, TB-500 and thymosin beta 4 are in Schedule 4 and in Appendix D clause 5, which makes possession without authority an offence. ^[9]

Other natural sequences have no individual entry. We searched the June 2026 text for thymosin alpha-1, KPV, MOTS-c and retatrutide and found none. GHK-Cu is not named, though "COPPER COMPOUNDS for human use" appear in Schedule 4 with exceptions, and we could not confirm from the text whether that entry captures GHK-Cu. ^[9] The TGA adds that a "research use only" label does not change whether a product is regulated as a therapeutic good. ^[12] Our guide to Australian peptide law and the Poisons Standard explains each schedule.

For sport, the WADA 2026 Prohibited List, effective 1 January 2026, names MOTS-c under S4.4.1 as an AMPK activator and BPC-157 as an example in S0. ^[33] Thymosin beta 4 and TB-500 appear in its index under S2. ^[33] GHK-Cu, KPV and thymosin alpha-1 are not named. S0 prohibits at all times any pharmacological substance not addressed elsewhere on the List and without current governmental approval for human therapeutic use. ^[33]

Peptides Collective sells several natural-sequence compounds for laboratory research use only, with a certificate for every batch. GHK-Cu comes in 50mg vials from A$58, thymosin alpha-1 in 10mg vials from A$118 and KPV in 10mg vials from A$58, dispatched from Western Australia with tracking. The GHK-Cu 50mg product page links the certificate for its current batch.

For laboratory reconstitution we stock BAC Water in 3ml vials for A$8. Our guide on how to reconstitute peptides covers solvents and concentrations in mg per mL.

Researchers study naturally occurring peptides because each one is a working signal with a known sequence and target, and that makes it the best starting template for new molecules. Many approved peptide medicines are modified versions of those templates, built to survive enzymes the native sequence cannot. For a research vial, natural origin settles nothing about purity, identity or legal status: the Poisons Standard entry settles the law, and the batch certificate settles what is in the vial.