What Are Peptides? Research Peptides UK

Last updated 15 October 2026 · SARMs Store editorial team. Products on this site are supplied strictly for laboratory research and are not for human consumption. This guide explains peptide chemistry and the research peptide market in general terms; it is not medical advice and contains no instructions for use. 18+ only.

Peptides are short chains of amino acids, the same building blocks that make up proteins. Some are natural hormones, some are licensed medicines, and many more are sold in the UK as research materials for laboratory work. This guide explains what peptides are chemically, how research peptides differ from medicines, why they come as freeze-dried powder, how their identity and purity are tested, and where they stand in UK law.

What are peptides?

A peptide is a chain of amino acids joined by peptide bonds. Chains of roughly 2 to 50 amino acids are usually called peptides; longer chains that fold into complex shapes are usually called proteins.

Peptides are everywhere in biology. Many hormones are peptides, including oxytocin (9 amino acids), ghrelin (28), glucagon (29) and growth hormone releasing hormone (44). Insulin, at 51 amino acids across two chains, sits on the border between peptide and protein. Peptides also act as signalling molecules in the immune and nervous systems, and they are produced by many plants, animals and microbes.

Peptide chemistry in plain terms

Each amino acid has an amino group at one end and a carboxyl group at the other. A peptide bond forms when the carboxyl group of one amino acid joins the amino group of the next, releasing a molecule of water, and repeating that link builds a chain.

Sequence and structure

The order of amino acids, read from the amino end (the N-terminus) to the carboxyl end (the C-terminus), is called the sequence, and it defines the peptide. Twenty standard amino acids are coded by genes, so even a short chain can exist in an enormous number of forms. Changing a single amino acid can change how a peptide binds its receptor, how quickly enzymes break it down, or both.

Modified amino acids

Many research peptides contain building blocks that do not occur in natural proteins. Examples include D-amino acids (mirror image forms that enzymes struggle to cut), aminoisobutyric acid (Aib), and an amidated C-terminus. Ipamorelin, for instance, has the sequence Aib-His-D-2Nal-D-Phe-Lys-NH2, which includes three non-standard units. These changes are usually made to slow breakdown or to make the peptide more selective for one receptor.

Peptides versus proteins

There is no single scientific cut-off between a long peptide and a small protein. Regulators draw their own lines: since 2020 the US Food and Drug Administration has interpreted the term protein to mean an amino acid polymer of more than 40 amino acids with a defined sequence, so shorter chains are regulated as peptides there. Size matters in practice because longer chains fold into stable three dimensional structures, while most short peptides are flexible in solution.

A short history of peptide science

Peptide science began with natural hormones and moved to fully synthetic chains in the second half of the twentieth century. Four Nobel Prizes mark the main steps.

Insulin, 1920s: Banting and Macleod shared the 1923 Nobel Prize in Physiology or Medicine for the discovery of insulin, the first peptide hormone used as a medicine.
The first synthetic peptide hormone, 1950s: Vincent du Vigneaud received the 1955 Nobel Prize in Chemistry for the first synthesis of a polypeptide hormone, oxytocin.
Reading a sequence, 1950s: Frederick Sanger received the 1958 Nobel Prize in Chemistry for his work on the structure of proteins, especially insulin, the first protein whose full sequence was determined.
Solid-phase synthesis, 1960s: Bruce Merrifield described solid-phase peptide synthesis in 1963 and received the 1984 Nobel Prize in Chemistry for it. Building the chain on a resin bead, one amino acid at a time, is still how most peptides are made today.

A 2021 review in Nature Reviews Drug Discovery by Muttenthaler and colleagues counted more than 80 peptide drugs on the market for conditions including diabetes, cancer, osteoporosis, multiple sclerosis and HIV infection.

How research peptides differ from medicines

A licensed peptide medicine and a research peptide can share the same sequence, but they are different products. A medicine has been made, tested and authorised for use in people; a research peptide is a chemical supplied for laboratory work and has not been assessed for human use.

The differences are practical as well as legal:

Authorisation: a medicine holds a marketing authorisation from a regulator such as the MHRA, granted on clinical trial evidence of quality, safety and efficacy for a defined use. A research peptide has no such authorisation.
Manufacture: medicines are made under Good Manufacturing Practice, with validated processes and release testing of every production lot. Research materials are made to a chemical specification for laboratory use.
Information: a medicine comes with prescribing information and a patient leaflet. A research peptide comes with chemical data, such as identity and purity, and no instructions for human use.
Monitoring: licensed medicines are subject to ongoing safety monitoring. Research materials are not.

Some compounds have been both. Tesamorelin is licensed in the United States under the brand Egrifta, and sermorelin was once licensed there as Geref, yet neither holds a UK licence. Research vials of either are not the licensed product. The growth hormone peptides comparison explains those histories.

How research peptides are made

Most research peptides are built by solid-phase peptide synthesis, purified by chromatography and then freeze-dried into a powder. The finished material is usually a salt, such as an acetate or trifluoroacetate, rather than the bare peptide.

In solid-phase synthesis the first amino acid is anchored to a resin, and each further amino acid is added in turn, with protecting groups (commonly Fmoc) stopping unwanted reactions. When the chain is complete it is cut from the resin, the protecting groups are removed, and the crude peptide is purified, typically by preparative reversed-phase HPLC. Each step can leave traces of incomplete or altered chains, which is why testing matters.

Lyophilised vials and reconstitution

Research peptides are usually supplied lyophilised, meaning freeze-dried into a dry powder or cake in a sealed vial. Removing the water makes most peptides far more stable in storage and transit than they would be in solution.

What lyophilisation is

Lyophilisation, or freeze-drying, freezes a peptide solution and then removes the ice under vacuum by sublimation, so water passes straight from solid to vapour. A secondary drying stage removes most of the remaining bound water. The process is used throughout the pharmaceutical industry for products that are unstable in water, and the US FDA publishes an inspection guide to it.

Reconstitution as a laboratory step

Before most laboratory work, a lyophilised peptide is reconstituted: a suitable diluent, such as sterile water or bacteriostatic water, is added to the vial so the powder dissolves back into solution. The right diluent and concentration depend on the peptide's solubility and on the experiment, and they should come from the research method being followed, not from a product listing. Once in solution most peptides degrade far faster than in powder form. Our bacteriostatic water research guide covers the diluent itself.

Storage

Sealed lyophilised vials are generally kept refrigerated or frozen, dry and away from light. Repeated freezing and thawing of a solution is avoided because it can break peptides down.

How peptides are tested

Two tests answer the two most important questions about a research peptide. HPLC shows how pure the material is, and mass spectrometry shows whether it is the right molecule.

HPLC: purity

High performance liquid chromatography pushes a dissolved sample through a packed column, and different molecules leave the column at different times. A detector records each one as a peak. Purity is usually reported as the main peak's share of the total peak area, so a figure of 98% means about 2% of the detected material is something else, typically closely related peptide impurities.

Mass spectrometry: identity

Mass spectrometry ionises the sample and measures the mass of the molecules present. If the measured mass matches the expected molecular weight of the peptide's sequence, that supports its identity. A peptide can be pure but wrong, or right but impure, which is why the two tests are read together.

What the tests can and cannot show

A 2014 review by D'Hondt and colleagues in the Journal of Pharmaceutical and Biomedical Analysis set out the impurities commonly found in peptide products: chains missing an amino acid (deletions) or carrying an extra one (insertions), amino acids flipped into the wrong mirror image form, oxidised side chains, joined pairs of chains, leftover trifluoroacetate, and in some cases unrelated peptides from poor manufacturing practice. Some of these have almost the same mass as the target, so a full picture can need more than one method. Other tests, such as net peptide content, water content and endotoxin, answer further questions. Our guide to reading a certificate of analysis explains how to read these reports.

Common research peptide families

Research peptides are usually grouped by the system they are studied in. The main families in the UK research market are growth hormone secretagogues, tissue repair peptides, copper peptides and mitochondrial peptides.

Growth hormone secretagogues: GHRH analogues such as sermorelin, CJC-1295 and tesamorelin, and ghrelin mimetics such as ipamorelin. See the growth hormone peptides comparison.
Tissue repair peptides: BPC-157, a 15 amino acid sequence derived from a gastric protein, and TB-500, a synthetic peptide based on part of thymosin beta-4. See the BPC-157 research guide and TB-500 research guide.
Copper peptides: GHK-Cu, the tripeptide glycyl-histidyl-lysine bound to copper. See the GHK-Cu research guide.
Mitochondrial peptides: MOTS-c, which is encoded in mitochondrial DNA, and the synthetic tetrapeptide SS-31. See the MOTS-c research guide and SS-31 research guide.
Melanocortin peptides: PT-141 (bremelanotide), which is licensed in the United States under the brand Vyleesi. See the PT-141 research guide.

NAD+ is often sold alongside peptides but is not one: it is a coenzyme built from nucleotides, not amino acids. The full range is on our research peptides collection.

Peptides compared with SARMs and small molecules

Peptides are larger and more fragile than typical small molecule research compounds such as SARMs. Most are broken down in the gut and by enzymes in the blood, which is why so much peptide chemistry is about stability.

A typical SARM has a molecular weight of a few hundred and is stable as a dry solid or in solution. A peptide such as tesamorelin weighs about 5,000. That size lets peptides bind receptors with high selectivity, but it also makes them sensitive to heat, moisture, light and enzymes. The SARMs vs peptides guide compares the two classes in more detail.

UK legal position for research peptides

Most research peptides are not controlled drugs in the UK, so they are legal to buy and possess for research. They are, however, unlicensed, so they cannot lawfully be sold, supplied or advertised for human use.

Misuse of Drugs Act 1971

The common research peptides, including BPC-157, TB-500, GHK-Cu, CJC-1295 and ipamorelin, are not listed under the Misuse of Drugs Act 1971. A few related hormones are: somatropin (growth hormone) and chorionic gonadotrophin are listed in Part III of Schedule 2 to the Act. Always check a specific compound rather than assuming every peptide is treated the same.

Medicines regulation

Under the Human Medicines Regulations 2012, a product is a medicine if it is presented as treating or preventing disease, or if it is used in or given to people to restore, correct or modify physiological functions. The MHRA's guidance on borderline products explains how it decides. A research peptide sold with claims about health, or with instructions for human use, would be treated as an unlicensed medicine. That is why legitimate UK suppliers sell research peptides strictly for laboratory use, with no instructions for human use.

Sport

Many peptides are prohibited in sport. Section S2 of the World Anti-Doping Agency Prohibited List covers peptide hormones, growth factors and related substances, including the growth hormone secretagogues, and the list is updated every year.

What to check before buying research peptides

A good research peptide listing tells you exactly what is in the vial and how it was tested. Look for the points below before you buy.

The exact compound and form, for example CJC-1295 with or without DAC.
The milligram content per vial.
HPLC purity and mass spectrometry identity for the material supplied.
Lyophilised powder in a sealed vial, with storage guidance.
A UK supplier that sells for research use only and gives no instructions for human use.

Frequently asked questions

What is a peptide in simple terms?

A short chain of amino acids linked by peptide bonds. Chains of roughly 2 to 50 amino acids are usually called peptides, and longer chains are usually called proteins.

What is the difference between a peptide and a protein?

Mainly size and structure. Proteins are longer and fold into stable three dimensional shapes. There is no single scientific cut-off, though US regulators treat chains of more than 40 amino acids as proteins.

Are research peptides the same as peptide medicines?

No. A medicine has been manufactured, tested and authorised for use in people. A research peptide is a chemical supplied for laboratory work and has not been assessed or authorised for human use, even when its sequence matches a licensed drug.

Why are peptides sold as a powder?

They are lyophilised (freeze-dried) because most peptides are far more stable as a dry powder than in solution. The powder is reconstituted with a suitable diluent as a laboratory step before use in research.

How is peptide purity measured?

Usually by HPLC, which separates the peptide from impurities and reports the main peak as a percentage of the total. Mass spectrometry is used alongside it to confirm the molecule's identity.

Are peptides legal in the UK?

Most research peptides are not controlled drugs, so they are legal to buy and possess for research. They are unlicensed, so they cannot be sold or advertised for human use. Growth hormone itself is a listed substance under the Misuse of Drugs Act.

Is NAD+ a peptide?

No. NAD+ is a coenzyme made from nucleotides, not amino acids, although it is often sold in the same ranges as research peptides.

Sources

Muttenthaler M, King GF, Adams DJ, Alewood PF. Trends in peptide drug discovery. Nature Reviews Drug Discovery. 2021;20(4):309-325.
Lau JL, Dunn MK. Therapeutic peptides: historical perspectives, current development trends, and future directions. Bioorganic and Medicinal Chemistry. 2018;26(10):2700-2707.
D'Hondt M, Bracke N, Taevernier L, et al. Related impurities in peptide medicines. Journal of Pharmaceutical and Biomedical Analysis. 2014;101:2-30.
Kojima M, Hosoda H, Date Y, et al. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999;402(6762):656-660.
Guillemin R, Brazeau P, Böhlen P, et al. Growth hormone-releasing factor from a human pancreatic tumor that caused acromegaly. Science. 1982;218(4572):585-587.
Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. European Journal of Endocrinology. 1998;139(5):552-561.
US Food and Drug Administration. Definition of the term "biological product". Federal Register, 21 February 2020.
US Food and Drug Administration. Lyophilization of parenteral (7/93). Inspection guide.
The Nobel Prize. The Nobel Prize in Physiology or Medicine 1923 (insulin).
The Nobel Prize. The Nobel Prize in Chemistry 1955 (du Vigneaud, oxytocin).
The Nobel Prize. The Nobel Prize in Chemistry 1958 (Sanger, insulin structure).
The Nobel Prize. The Nobel Prize in Chemistry 1984 (Merrifield, solid-phase synthesis).
Misuse of Drugs Act 1971, Schedule 2. legislation.gov.uk.
The Human Medicines Regulations 2012. legislation.gov.uk.
Medicines and Healthcare products Regulatory Agency. Borderline products: how to tell if your product is a medicine. GOV.UK.
World Anti-Doping Agency. Prohibited List, section S2.

This guide summarises published research and is for laboratory reference only. Products are not for human consumption.

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What Are Peptides? Research Peptides Explained, UK 2026