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In short: a peptide is a short chain of amino acids joined by peptide bonds — typically fewer than 50, which is what separates a peptide from a protein. In the body they act as signalling molecules, binding receptors on the cell surface to trigger a specific response. Research peptides are synthetic copies or modified analogues of these sequences, supplied as lyophilised powder for laboratory use.
- A peptide is amino acids linked by peptide bonds — the same chemistry as a protein, at a shorter length.
- Most act at cell-surface receptors, triggering signalling cascades rather than entering the cell to alter transcription directly.
- Their defining practical trait is fragility: they are degraded by enzymes, are not meaningfully orally bioavailable, and need reconstitution and cold storage.
- The class is broad. Growth hormone secretagogues, tissue repair peptides, mitochondrial peptides and immune modulators share a chemistry but very little else.
- Unlike SARMs, the peptide class includes approved medicines — insulin and GLP-1 agonists among them — though the specific compounds sold as research materials are not approved.
- Several products shelved alongside peptides — NAD+, methylene blue, 5-Amino-1MQ — are not peptides at all.
What is a peptide?
Amino acids are the building blocks. Each has an amino group at one end and a carboxyl group at the other, and when the carboxyl group of one reacts with the amino group of the next, the two join and a molecule of water is released. That bond is a peptide bond, and a chain of them is a peptide.
The sequence of amino acids is the entire identity of the molecule. Change one residue and you have a different compound with potentially different receptor affinity — which is why sequence verification, not just purity, matters when you receive material.
Where peptides end and proteins begin
The boundary is conventional rather than chemical. Chains of roughly 50 amino acids or fewer are called peptides; longer chains are proteins. Insulin, at 51 residues, sits right on the line and is described either way depending on the paper you are reading — our guide to peptides vs proteins works through the boundary in detail. Shorter chains have their own names: two residues make a dipeptide, three a tripeptide, and up to around twenty an oligopeptide.
Scale is easier to grasp with examples from a single catalogue. KPV is three amino acids. BPC-157 is fifteen. MOTS-c is sixteen. Thymosin alpha-1 is twenty-eight. All are peptides; the shortest is roughly a tenth the size of the longest.
How peptides work
Most peptides are too large and too polar to cross the cell membrane. Rather than entering the cell, they bind a receptor embedded in its surface — very often a G protein-coupled receptor — and the message is relayed inward by second messengers such as cyclic AMP. One peptide binding one receptor can trigger a cascade that amplifies through the cell.
This has three consequences that shape how the class behaves in research.
- High specificity. Receptor binding depends on the three-dimensional shape the sequence folds into, so a peptide typically engages a narrow set of receptors. This is the appeal of the class: precision.
- Short duration. Peptidases in blood and tissue break peptide bonds continuously. Many native peptides have half-lives measured in minutes, which is precisely why so much synthetic work has gone into extending them.
- Poor oral bioavailability. Digestive proteases treat a peptide like any other dietary protein, and the fragments that survive struggle to cross the intestinal wall. This is a genuine chemical constraint, not a formulation preference.
How analogues get around the fragility
Much of modern peptide chemistry is about making a sequence last longer without losing what it does. Common strategies include substituting D-amino acids that peptidases do not recognise, cyclising the chain so there is no exposed terminus to attack, attaching polyethylene glycol to slow clearance, and adding a group that binds circulating albumin so the peptide travels attached to a much larger carrier.
That last approach is what the "DAC" in CJC-1295 (DAC) refers to — a drug affinity complex that binds albumin and extends the half-life of a GHRH analogue from minutes to considerably longer. The unmodified version of the same sequence clears far more quickly. Same core peptide, entirely different pharmacokinetic profile.
Almost all are made by solid-phase peptide synthesis, the method Bruce Merrifield won a Nobel Prize for in 1984. The chain is built one residue at a time on a solid resin, then cleaved, purified by reverse-phase HPLC and freeze-dried. What arrives in the vial is a white lyophilised powder, usually as an acetate salt. Purity in this context means how much of the material is the intended sequence rather than truncated or deletion sequences from incomplete coupling steps.
The main categories of research peptide
"Peptide" describes a chemistry, not a function. Grouping by what the sequence actually targets is far more useful, and the categories below cover most of what appears in the literature.
Growth hormone secretagogues and GHRH analogues
The largest group by volume. These do not supply growth hormone; they act on the pituitary to influence its own release. Two distinct receptor families are involved, which is a distinction often lost in general write-ups.
- Ghrelin receptor agonists — Ipamorelin, GHRP-2 and GHRP-6 act at GHS-R1a. Ipamorelin is the most receptor-selective of the three in published comparisons; GHRP-6 is notable in the literature for a pronounced appetite effect.
- GHRH analogues — CJC-1295 and Tesamorelin mimic growth hormone-releasing hormone at its own receptor. Tesamorelin is one of the few compounds in this catalogue with an approved medicine counterpart, licensed for HIV-associated lipodystrophy.
Tissue repair and regeneration
BPC-157 is a fifteen-residue sequence derived from a protein found in gastric juice, studied extensively in rodent models of tendon, ligament, muscle and gut injury. TB-500 relates to thymosin beta-4, a protein central to actin regulation and cell migration. GHK-Cu is a copper-binding tripeptide studied in wound healing and skin remodelling, and is also available in capsule format.
Mitochondrial and metabolic peptides
MOTS-c is unusual: it is encoded in mitochondrial rather than nuclear DNA, one of a small set of mitochondrial-derived peptides identified since 2015 and studied in metabolic regulation. SS-31 takes a different approach, associating with cardiolipin in the inner mitochondrial membrane and studied for effects on mitochondrial efficiency. Our guide to mitochondrial health covers both in the context of how mitochondrial function is measured.
Immune and inflammatory modulators
Thymosin alpha-1 is a 28-residue peptide originally isolated from thymus tissue and studied in immune modulation; it is an approved medicine in a number of countries. KPV is the tripeptide tail of alpha-MSH and retains anti-inflammatory activity in models despite its very small size — a useful demonstration that potency does not track with length.
Neuroendocrine and signalling peptides
PT-141 is a melanocortin receptor agonist and, as bremelanotide, an approved medicine in the United States. Kisspeptin-10 acts upstream of the reproductive axis, stimulating GnRH release, and has been used as a research tool for probing that axis. Epitalon is a synthetic tetrapeptide from Russian pineal research; the literature around it is considerably thinner than for the others here, and worth reading critically.
Compounds shelved with peptides that are not peptides
Retail categories are organised by how customers shop, not by chemistry. Several popular research compounds sit in peptide catalogues without being peptides at all.
| Compound | What it actually is | Why the distinction matters |
|---|---|---|
| NAD+ | A dinucleotide coenzyme, not an amino acid chain | Different stability profile and a completely different role — it is a metabolic cofactor, not a signalling molecule |
| Methylene Blue | A small-molecule phenothiazine dye | Stable, orally active, and studied as a redox agent — none of the peptide handling constraints apply |
| 5-Amino-1MQ | A small-molecule enzyme inhibitor (NNMT) | Acts inside the cell on an enzyme, not at a surface receptor |
| MK-677 (Ibutamoren) | A non-peptide small molecule | Hits the same ghrelin receptor as the GHRPs while being chemically unrelated to them — a genuinely useful comparator |
MK-677 is the instructive case. It targets the identical receptor as Ipamorelin and the GHRPs, but because it is a small molecule rather than a peptide it is orally active and long-lasting — see our review of the MK-677 research. Same target, different chemistry, different experimental logistics entirely.
Peptides compared with SARMs and small molecules
If you work across both categories, the differences below matter more than the similarities. Our companion guide on selective androgen receptor modulators covers that class in the same depth.
| Property | Peptides | SARMs and small molecules |
|---|---|---|
| Structure | Amino acid chains, roughly 3–50 residues | Single synthetic molecules, typically under 500 Da |
| Receptor location | Usually cell-surface receptors | Intracellular — the ligand crosses the membrane |
| Mode of action | Signalling cascades via second messengers | Direct modulation of gene transcription |
| Oral activity | Generally poor; degraded by digestive proteases | Generally good; designed for oral bioavailability |
| Format supplied | Lyophilised powder requiring reconstitution | Ready-made solution or capsule |
| Stability | Sensitive to heat, light, agitation and freeze-thaw cycles | Robust under normal storage |
| Approved medicines in the class | Many — insulin, GLP-1 agonists, oxytocin, octreotide | None for SARMs specifically |
That last row is worth dwelling on. Peptide therapeutics are a well-established and growing category of approved medicine, which is a different starting position from SARMs — where no compound has been approved anywhere. It does not follow that any particular research peptide is safe or effective; it means the chemistry itself is well trodden.
What peptides are studied for
Research interest maps closely to the categories above. None of the following are approved uses for the compounds discussed here, and much of the work is preclinical.
Tissue repair and recovery models
The largest body of work around BPC-157 concerns healing in rodent models — tendon-to-bone, muscle crush, and gastrointestinal injury among them. The findings are consistent across a substantial number of studies from a relatively concentrated group of research teams, and human data is essentially absent. Both halves of that sentence matter when citing it. The BPC-157 research guide goes through that record in detail, including the proposed mechanisms and what separates the injectable and oral forms.
Growth hormone axis research
Secretagogues are used as tools for probing pituitary function, since they stimulate endogenous release rather than supplying exogenous hormone. Tesamorelin's approved indication came out of this line of work, and the various GHRPs remain useful for distinguishing ghrelin receptor signalling from GHRH receptor signalling.
Metabolic and mitochondrial function
MOTS-c has been studied in insulin sensitivity and metabolic homeostasis models since its identification, and SS-31 in mitochondrial dysfunction, including cardiac and renal models. This is among the more active areas of current peptide research.
Immune modulation
Thymosin alpha-1 has been examined in immune response and infection contexts across several decades, with an approved-medicine footprint in some jurisdictions. KPV appears in inflammatory bowel and skin inflammation models.
Skin, wound healing and cosmetic science
GHK-Cu is one of the better-studied peptides in dermatological research, examined for effects on collagen synthesis and wound remodelling, and it appears widely in cosmetic formulation literature.
What the research does not show
The same caveats apply here as to any emerging compound class, with one or two specific to peptides.
- Species gaps. Several of the most-cited peptides rest overwhelmingly on rodent data. Rodent healing models translate to humans inconsistently, and a strong rodent result is a hypothesis rather than a conclusion.
- Small, short studies. Where human data exists it usually comes from small cohorts over short periods, often with surrogate endpoints rather than clinical outcomes.
- Publication concentration. For some compounds a large share of the literature originates from a small number of groups. Independent replication is thinner than the raw citation count suggests.
- Purity and identity are not givens. Synthesis by-products — truncated sequences, deletion sequences, residual solvents — are invisible without analysis. Analyses of research chemicals sold online have repeatedly found content that does not match the label.
- Degradation is silent. A peptide that has been through repeated freeze-thaw cycles or stored warm may look identical in the vial while having lost much of its intended sequence integrity.
That final point is the one most likely to cost you an experiment. It is also the reason we publish full third-party analysis for every batch rather than a summary.
Reconstitution, storage and handling
Peptides demand more care than any other category on the shelf. The following is general laboratory practice for handling lyophilised material.
Before reconstitution
Lyophilised peptide is at its most stable as a dry powder. Keep vials sealed, cold and out of the light, and let a vial come to room temperature before opening — introducing a cold vial to humid air draws condensation onto the powder, and moisture is what starts degradation.
Reconstitution
Add the diluent slowly, running it down the inside wall of the vial rather than directing a stream onto the powder. Swirl gently to dissolve; do not shake. Foaming is a sign of mechanical stress on the peptide, and vigorous agitation can denature it. Bacteriostatic water — water containing 0.9% benzyl alcohol — is the usual choice where a solution needs to remain usable across multiple sessions, since the preservative suppresses microbial growth.
After reconstitution
Solutions are far less stable than powder. Refrigerate, keep away from light, and avoid repeated freeze-thaw cycles — each one damages a fraction of the material. Where a solution will be used across many sessions, aliquot into single-use portions at the start so that the bulk is disturbed once rather than repeatedly.
Verification and documentation
Ask for a certificate of analysis tied to the lot you received. HPLC establishes purity, mass spectrometry confirms the molecular weight and therefore the sequence identity. Record lot numbers against every experiment; when a result looks anomalous, lot-level traceability is what lets you investigate rather than guess. Our FAQ covers reconstitution and storage in more operational detail.
All compounds discussed in this guide are supplied strictly for laboratory and in-vitro research. They are not medicines, are not for human or veterinary use, and are not intended to diagnose, treat, cure or prevent any disease. Nothing here is medical advice or a protocol for administration.
Regulatory and legal status
The picture is more layered than for SARMs, because the peptide class spans approved medicines and unapproved research compounds at the same time.
- Some peptides are approved medicines — insulin, GLP-1 receptor agonists, oxytocin, octreotide, teriparatide and others. Approval attaches to a specific product for a specific indication, never to the chemistry in general.
- The research peptides in this catalogue are not approved for human use, and are supplied as laboratory reference materials only.
- Prohibited in sport. Peptide hormones, growth factors and growth hormone secretagogues are covered by section S2 of the WADA Prohibited List, banned at all times.
- Research supply is distinct. Material correctly labelled and supplied for laboratory research, not marketed for human consumption, sits under a different framework — consistent with 21 C.F.R. §§ 312.2(b)(3) and 312.160.
Requirements vary by jurisdiction and change over time. Institutions should confirm their local position before ordering.
Frequently asked questions
What is a peptide, simply?
A short chain of amino acids joined by peptide bonds — the same chemistry as a protein, at a shorter length. Chains of roughly 50 amino acids or fewer are called peptides; anything longer is generally called a protein.
What is the difference between a peptide and a protein?
Length, by convention rather than chemistry. Both are amino acids joined by peptide bonds. The customary dividing line sits around 50 residues, which is why insulin at 51 is described both ways depending on the source.
How do peptides differ from SARMs?
Peptides are amino acid chains that usually act at cell-surface receptors and trigger signalling cascades. SARMs are small synthetic molecules that cross the cell membrane and act on the intracellular androgen receptor to alter gene transcription. They also differ in handling: peptides arrive lyophilised and need reconstitution and cold storage, while SARMs are supplied ready to use.
Why do research peptides need reconstitution?
They are supplied freeze-dried because peptides are far more stable as a dry powder than in solution. Reconstitution with a suitable diluent — commonly bacteriostatic water — returns the material to a usable liquid form, after which it must be refrigerated and protected from light.
Is NAD+ a peptide?
No. NAD+ is a dinucleotide coenzyme, not a chain of amino acids. It is frequently sold alongside peptides but belongs to a different chemical class entirely, as do methylene blue and 5-Amino-1MQ.
How is the purity of a research peptide verified?
By independent analysis of the specific lot: HPLC to establish purity, and mass spectrometry to confirm molecular weight and therefore sequence identity. Both should appear on a certificate of analysis tied to your lot number, and the report should be unredacted.
Selected reading
Starting points in the primary literature — each title links to its record on PubMed. These are provided for reference and are not endorsements of any particular finding.
- Merrifield RB. Solid phase peptide synthesis. I. The synthesis of a tetrapeptide. Journal of the American Chemical Society, 1963.
- Fosgerau K, Hoffmann T. Peptide therapeutics: current status and future directions. Drug Discovery Today, 2015.
- Lau JL, Dunn MK. Therapeutic peptides: historical perspectives, current development trends, and future directions. Bioorganic & Medicinal Chemistry, 2018.
- Sikiric P, et al. Stable gastric pentadecapeptide BPC 157: novel therapy in gastrointestinal tract. Current Pharmaceutical Design, 2011.
- Lee C, et al. The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis and reduces obesity and insulin resistance. Cell Metabolism, 2015.
- Pickart L, Margolina A. Regenerative and protective actions of the GHK-Cu peptide. International Journal of Molecular Sciences, 2018.
- Sinha DK, et al. Beyond the androgen receptor: the role of growth hormone secretagogues. Translational Andrology and Urology, 2020.
- World Anti-Doping Agency. Prohibited List, section S2, Peptide Hormones, Growth Factors, Related Substances and Mimetics.
Continue reading
Every batch is independently tested for purity and identity, individually lot-tracked, and the full report is published before listing.
This guide is provided for educational and informational purposes only and is based on published research. Core Labs supplies research chemicals for laboratory use exclusively. Products are not approved for human consumption, nor for medical, veterinary or household use.