Peptide Drugs Explained: Definition, Approved Examples and How They Are Designed

Peptide drugs are medicines whose active ingredient is a short, defined chain of amino acids: bigger than a typical small-molecule drug, smaller than a protein. More than 80 have reached the market since insulin was first given to a patient in Toronto in 1922, from hormone copies to antibiotics, cancer radioligands and the GLP-1 medicines. For anyone working with research peptides, they are also the reference point for what a peptide must go through before it can be called a medicine.

This guide covers what counts as a peptide drug, how many are approved, the history, the main classes of peptide therapeutics, the chemistry that makes them last, how they are made and how they differ from research peptides.

What is a peptide drug?

A peptide drug is a medicine whose active ingredient is a peptide: a chain of amino acids joined by peptide bonds, with a defined sequence. Our guide to what peptides are covers the chemistry. Small molecules typically weigh under 500 g/mol and biologics over 5,000 g/mol; most peptide drugs fall in between. There is no universal cut-off. One nomenclature body uses 2 to 50 residues, and the European Medicines Agency, according to the PepTherDia authors, classifies peptides partly by how they are made.

The US Food and Drug Administration (FDA) line matters most in practice. Under 21 CFR 600.3(h)(6), a protein is an alpha amino acid polymer with a specific, defined sequence of more than 40 amino acids, and chains that associate in nature are counted together. On March 23, 2020, approved drug applications for biological products, including insulin, insulin analogues and human growth hormone, were deemed to be biologics licences; peptides of 40 or fewer amino acids were not affected. Insulin is therefore a protein in US regulatory terms, while octreotide and semaglutide are still approved as drugs. Fusion to a large carrier changes the category too: dulaglutide, a GLP-1 analogue joined to an antibody Fc portion, is licensed as a biologic.

How many peptide drugs are approved?

More than 80, on the most cited estimate. A 2021 review in Nature Reviews Drug Discovery counted more than 80 on the market, in areas including diabetes, cancer, osteoporosis, multiple sclerosis, HIV infection and chronic pain. A 2022 review agreed, adding that 33 non-insulin peptide drugs had been approved since 2000 and more than 170 peptides were in clinical development. The PepTherDia database counted 89 peptide drugs and 16 diagnostics approved in North America, Europe and Japan by November 2020; 47% contain at least one ring and 13% carry a lipophilic carbon chain. A 2026 review counted 34 FDA peptide approvals from 2016 to 2024, plus one among the 46 novel drugs of 2025. Counts differ with the size cut-off, with whether insulins, diagnostics and conjugates are included, and with which regulators are counted.

A century of peptide medicines, from Toronto to GLP-1

The first peptide drug is a Canadian story. Frederick Banting first visited J.J.R. Macleod, chair of physiology at the University of Toronto, in November 1920. By August 1921 Banting and Charles Best had a pancreatic extract that lowered blood sugar in diabetic dogs, and that December the biochemist James Collip joined to purify it for human testing. On January 23, 1922, at Toronto General Hospital, 14-year-old Leonard Thompson became the first person to receive the purified extract. John FitzGerald, director of the university’s Connaught Antitoxin Laboratories, had put Collip and Best in charge of production, and by the autumn of 1922 Connaught insulin was in clinical use in Toronto. The university held the patent rights and Connaught set its prices by cost. Banting and Macleod shared the 1923 Nobel Prize “for the discovery of insulin”, the year insulin became the first commercial peptide drug. Our history of Canada’s century of peptide discovery follows the thread further.

In 1953 Vincent du Vigneaud’s group synthesized oxytocin, honoured in 1955 as the first synthesis of a polypeptide hormone. In 1963 R. Bruce Merrifield introduced solid-phase peptide synthesis, and in 1982 recombinant human insulin became the first medical product of any kind made with recombinant DNA. Designed peptides followed: leuprolide (1985), octreotide (1988), the HIV fusion inhibitor enfuvirtide (2003) and exenatide (2005), the first GLP-1 receptor agonist, developed from Gila monster venom, where exendin-4 was found in 1992.

Toronto returned through the glucagon-like peptides. In 1996 Daniel Drucker, Patricia Brubaker and colleagues at Mount Sinai Hospital and the University of Toronto showed that GLP-2, a 33-amino-acid peptide with no known function at the time, drove intestinal growth in mice; the GLP-2 analogue teduglutide was approved in the US in 2012. Drucker shared the 2021 Canada Gairdner International Award with Joel Habener and Jens Holst for research on glucagon-like peptides.

The main classes of peptide drugs, and what they are used for

Peptide drugs are used across diabetes, cancer, osteoporosis, multiple sclerosis, HIV infection and chronic pain, and some serve as diagnostic agents. By structure, they fall into a few classes:

• Hormone analogues copy and improve natural hormones: insulin, GnRH, somatostatin, GLP-1 and GLP-2. Our guide to peptide hormones explains the originals.
• Natural-product cyclic peptides come from microbes. Nearly half of marketed peptides contain a ring; ciclosporin, an 11-residue cyclic peptide from the fungus Beauveria nivea, was approved in 1983, including as an oral solution.
• Antimicrobial lipopeptides and glycopeptides include daptomycin (2003), a cyclic lipopeptide that depolarizes bacterial membranes, and vancomycin, a glycopeptide that blocks cell-wall synthesis. Host-defence peptides such as LL-37 are a separate family; see our antimicrobial peptides guide.
• Radioligands and peptide–drug conjugates use the peptide as a homing device. Lutetium-177 dotatate binds somatostatin receptor subtype 2, is taken into the cell and damages it with beta radiation. A 2025 review counted about 300 conjugates entering trials against three FDA approvals as medicines, one withdrawn seven months after its US launch.
• Stapled peptides lock a helix with a hydrocarbon brace. The 2004 proof of concept was protease-resistant and cell-permeable, and inhibited human leukemia xenografts in an animal model.

Why natural peptides make poor drugs, and the fixes

Natural peptides are cleared fast. A 2015 review of peptide absorption, distribution, metabolism and excretion names proteolysis, renal clearance and low permeability as the core problems. The enzyme DPP-4 breaks down GLP-1 and GLP-2, and the gut is a formidable barrier: as Drucker’s 2020 review notes, protein and peptide drugs have generally needed parenteral administration, by routes that bypass the digestive tract. The fixes:

• Protect the backbone. D-amino acids (octreotide, leuprolide), rings (octreotide, ciclosporin), N-methylation (ciclosporin) and capped ends (enfuvirtide). Teduglutide’s single glycine-for-alanine swap blocks DPP-4 and stretches GLP-2’s half-life from about 7 minutes to about 2 hours. See D-amino acids explained.
• Ride on albumin. Liraglutide’s 16-carbon palmitic acid, attached through a glutamic-acid spacer, supports plasma protein binding; semaglutide binds albumin more strongly and had a 46.1-hour plasma half-life in minipigs.
• Get bigger. Peginesatide (2012) carried a 40 kDa PEG chain and was withdrawn a year later; dulaglutide’s Fc fusion makes a molecule of about 63 kDa. Our guide to half-life engineering goes deeper.
• Cross the gut. Semaglutide tablets contain the enhancer SNAC. In the 2018 mechanism study, absorption took place in the stomach next to the tablet; SNAC buffered against enzymatic breakdown and raised absorption briefly, through cells rather than between them, and the effect was compound-specific.

How peptide drugs are made

Chemical synthesis builds the chain on a solid support, Merrifield’s 1963 method. Fmoc chemistry is often preferred for its milder deprotection, and chains under about 50 residues are relatively routine; enfuvirtide, at 36 residues, is fully synthetic. Recombinant expression uses engineered cells: E. coli for teduglutide, Chinese hamster ovary cells for dulaglutide. Hybrid routes combine the two: liraglutide’s precursor is expressed in yeast and its fatty acid attached afterwards. See how peptides are synthesized.

Marketed peptides are made under good manufacturing practice (GMP), set out for active ingredients in the ICH Q7 guideline, which the FDA issues as guidance. The impurities that matter most are closely related peptides. For synthetic versions of five peptides first made by recombinant DNA, including liraglutide and teduglutide, FDA guidance expects each peptide-related impurity at 0.10% or more to be identified, no new impurity above 0.5%, and any new one in between to be justified for safety, effectiveness and immunogenicity. That is why our HPLC testing guide presents a purity figure as the start of the analysis, not the end.

Where peptide drug development is heading

More than 170 peptides were in clinical development at the time of the 2022 review, and the 2021 review highlights venomics and peptide display libraries as discovery engines. Threads to watch include multi-receptor agonists (tirzepatide activates both the GIP and GLP-1 receptors), oral delivery beyond semaglutide, peptide–drug conjugates designed with artificial-intelligence tools, and stapled or macrocyclic peptides aimed at protein–protein interactions inside cells.

Approved peptide drugs vs research peptides

An approved peptide drug is a specific product: made by a defined process under GMP, tested in phased clinical trials and reviewed by regulators for a stated use. The approval belongs to that product, not to an amino-acid sequence; our explainer on clinical trial phases covers the testing.

A research peptide sold as a laboratory reagent has not been through clinical development as a product and is not for human or veterinary use, even when its sequence matches a peptide in clinical papers. Its documentation answers laboratory questions, such as identity, batch purity and peptide content, and says nothing about safety or efficacy in people. Our guide to what peptide grade labels mean explains the terminology.

What’s established and what isn’t

Sourcing research peptides in Canada

If you buy peptides for laboratory work, judge a reagent by its documentation, not its label. Before ordering research peptides in Canada:

• Ask for a batch-matched certificate with HPLC purity and a mass-spectrometry identity check, and match its batch number to the vial; our COA guide lists what else to look for.
• Look past the headline purity figure to the main impurity peaks.
• Store freeze-dried material cold, dry and dark; see the peptide storage guide.
• Compare suppliers on documentation using our guides to research peptides in Canada and choosing a Canadian peptide supplier.

The reagents below relate to the classes above. They are research materials for laboratory study, not medicines.

LL-37The only human cathelicidin, a natural antimicrobial peptide studied in the laboratoryView product GHRP-6A synthetic hexapeptide with two D-amino acids, first described in 1984View product GHRP-2From the same growth hormone-releasing peptide series as GHRP-6View product

Frequently asked questions