Plain-language definitions of the terms you will meet when reading peptide research, certificates of analysis and clinical trials. Written to help you read the literature, not to give usage instructions.
A
Agonist
A molecule that binds to a receptor and activates it. The opposite is an antagonist, which binds but blocks activation. Many research peptides are classified by which receptor they act on as agonists, for example GLP-1 receptor agonists.
Amino acid
The building block of peptides and proteins. Twenty standard amino acids are encoded by DNA; synthetic peptides can also contain modified or non-natural amino acids.
Amylin
A peptide hormone co-secreted with insulin that is studied for its role in appetite and glucose regulation. Cagrilintide is a long-acting amylin analogue used in metabolic research.
Analogue
A compound whose structure has been deliberately modified from a natural molecule, for example to change stability, receptor selectivity or duration of action in studies. Tirzepatide, tesamorelin and IGF-1 LR3 are analogues.
Antagonist
A molecule that binds to a receptor without activating it, blocking the action of an agonist.
B
Bacteriostatic water
Sterile water containing 0.9% benzyl alcohol, which inhibits bacterial growth. See bacteriostatic vs sterile water.
Batch (lot) number
The identifier that links a vial to a specific production run and its test results. A genuine certificate of analysis always names the batch it covers.
C
Certificate of analysis (COA)
A laboratory document reporting results for one specific batch, typically purity by HPLC and identity by mass spectrometry. Read how to read a peptide COA or browse the COA library.
Clinical trial phases
Phase 1 tests safety in a small group; phase 2 explores effects and side effects in larger groups; phase 3 confirms results in large, often randomised and placebo-controlled studies; phase 4 monitors a product after approval. See retatrutide phase 3 results for an example.
Counterion (TFA salt)
Purified peptides are often supplied as salts. Trifluoroacetic acid (TFA), used during synthesis and HPLC purification, commonly remains as the counterion. It adds weight to the powder, which is why net peptide content matters.
Cyclic peptide
A peptide whose ends or side chains are joined to form a ring, which can improve stability. Melanotan II and PT-141 are cyclic melanocortin analogues.
D
DAC (drug affinity complex)
A chemical modification that lets a peptide bind to serum albumin and stay in circulation longer. CJC-1295 with DAC carries this modification; CJC-1295 without DAC does not.
Dalton (Da)
The unit of molecular mass. Mass spectrometry reports a peptide mass in daltons, which is compared with the theoretical mass of its sequence to confirm identity.
E
Endotoxin
A fragment of the outer membrane of gram-negative bacteria that can contaminate materials. It is measured with the LAL assay and is relevant to anything used in cell-based work.
F
Fragment
A shorter section of a larger natural protein or peptide, such as TB-500 (related to thymosin beta-4) or AOD-9604 (derived from the C-terminus of human growth hormone).
G
Ghrelin receptor (GHS-R1a)
The receptor that mediates growth hormone release in response to ghrelin. Ipamorelin is a selective agonist of this receptor and is classed as a growth hormone secretagogue.
GHRH (growth hormone-releasing hormone)
A hypothalamic peptide that stimulates the pituitary to release growth hormone. Tesamorelin and CJC-1295 are GHRH analogues. See CJC-1295 vs tesamorelin vs ipamorelin.
GIP (glucose-dependent insulinotropic polypeptide)
An incretin hormone released after eating. Dual agonists such as tirzepatide act on both the GIP and GLP-1 receptors.
GLP-1 (glucagon-like peptide-1)
An incretin hormone that enhances glucose-dependent insulin release and slows gastric emptying. Many metabolic research compounds target its receptor.
Glucagon receptor
The receptor for glucagon, a hormone that raises blood glucose and affects energy expenditure. Retatrutide is an investigational agonist at the GIP, GLP-1 and glucagon receptors.
H
Half-life
The time it takes for the concentration of a compound to fall by half. Chemical modifications such as DAC or lipidation are used to lengthen the half-life of peptides in studies.
HPLC (high-performance liquid chromatography)
A method that separates the components of a sample. For peptides, purity is reported as the percentage of the total peak area belonging to the main compound, usually measured by UV absorbance.
I
In vitro
Latin for in glass. Experiments performed on cells, tissues or molecules outside a living organism, such as receptor binding or cell culture assays.
In vivo
Experiments performed in a living organism, for example in animal models. In vivo results do not automatically predict effects in humans.
L
Lyophilization
Freeze-drying: water is removed by sublimation under vacuum, leaving a stable powder (the white cake seen in a vial). Lyophilised peptides are more stable in storage than peptides in solution. See how to store peptides.
M
Mass spectrometry (MS)
A method that measures the mass of molecules. It confirms that a peptide has the expected molecular mass, and therefore the expected identity, complementing the purity result from HPLC.
Melanocortin receptors
A family of five receptors (MC1R to MC5R) involved in pigmentation, appetite and other signalling. Melanotan I, Melanotan II and PT-141 are melanocortin agonists. See Melanotan I vs II.
Mitochondrial-derived peptide
A short peptide encoded within mitochondrial DNA. MOTS-c is a 16-amino-acid example studied for metabolic signalling. Read what MOTS-c is.
N
Net peptide content
The share of a vial’s powder that is actual peptide, as opposed to water and counterions. Gross weight and net peptide content are not the same thing.
P
Peptide
A short chain of amino acids joined by peptide bonds. By convention, chains of up to roughly 50 amino acids are called peptides and longer chains proteins. See peptides 101.
Peptide bond
The covalent bond between the carboxyl group of one amino acid and the amino group of the next, which links amino acids into a chain.
PMID
The unique identifier of an article in PubMed, the biomedical literature database of the US National Library of Medicine. We cite PMIDs so that every claim can be checked at the source.
Preclinical research
Studies performed before human trials, in cell cultures and animal models. Most research peptides have only preclinical data.
Purity
The proportion of a sample that is the target compound. For peptides it is usually reported by HPLC. High purity alone does not prove identity, which is why mass spectrometry is also needed.
R
Randomised, placebo-controlled trial
A study design in which participants are randomly assigned to the studied compound or a placebo, which reduces bias and is the standard for testing effects in humans.
Receptor
A protein on or in a cell that binds a specific molecule and triggers a response. Peptides act largely by binding receptors.
Reconstitution
The process of dissolving a lyophilised powder in a liquid to form a solution. Procedures and quantities are protocol-specific and are intentionally not covered on this site.
Research use only (RUO)
A label meaning a product is intended for laboratory research and not for human or veterinary use, consumption or diagnostic procedures. All TrueLabs products are RUO.
S
Secretagogue
A substance that stimulates the secretion of another substance. Growth hormone secretagogues stimulate the release of growth hormone.
Sequence
The order of amino acids in a peptide, written from the N-terminus to the C-terminus. The sequence determines the theoretical mass used to check identity by mass spectrometry.
Stability
How long a compound keeps its identity and purity under given storage conditions. Heat, moisture, light and repeated freeze-thaw cycles can degrade peptides.
T
Telomere
A repeating DNA sequence that caps chromosome ends and shortens with cell division. Epithalon (a four-amino-acid peptide) has been studied in cell and animal models for effects on telomerase. See what epitalon is.
Third-party testing
Testing performed by a laboratory independent from the manufacturer or seller. It is the basis for trusting a COA. See how to spot fake peptides.
Compounds at a glance
A quick reference to the research compounds in our catalogue. Status describes the type of evidence, not a recommendation.
| Compound | What it is | Evidence status |
|---|---|---|
| BPC-157 | 15-amino-acid synthetic peptide derived from a protein found in gastric juice | Preclinical |
| TB-500 | Synthetic fragment related to thymosin beta-4 | Preclinical |
| GHK-Cu | Copper-binding tripeptide (Gly-His-Lys) found naturally in plasma | Preclinical / cosmetic studies |
| KPV | Tripeptide (Lys-Pro-Val) from the C-terminus of alpha-MSH | Preclinical |
| Ipamorelin | Selective ghrelin receptor agonist (growth hormone secretagogue) | Clinical and preclinical |
| CJC-1295 | GHRH analogue, with or without DAC | Clinical and preclinical |
| Tesamorelin | GHRH analogue (44 amino acids) | Approved medicine in some countries |
| Retatrutide | GIP / GLP-1 / glucagon triple receptor agonist | Investigational, phase 3 |
| Tirzepatide | GIP / GLP-1 dual receptor agonist | Approved medicine under brand names |
| Cagrilintide | Long-acting amylin analogue | Clinical and preclinical |
| Semax | Analogue of ACTH(4-10) | Studied mainly in Russia |
| Selank | Analogue of the immune peptide tuftsin | Studied mainly in Russia |
| MOTS-c | Mitochondrial-derived peptide (16 amino acids) | Preclinical and early clinical |
| SS-31 | Mitochondria-targeted tetrapeptide (elamipretide) | Clinical and preclinical |
| Epithalon | Tetrapeptide Ala-Glu-Asp-Gly | Preclinical |
| PT-141 | Melanocortin receptor agonist (bremelanotide) | Approved medicine in some countries |
| Kisspeptin-10 | Ligand of the KISS1 receptor | Clinical and preclinical |
This glossary is educational. TrueLabs products are sold strictly for in vitro and laboratory research and are not for human or veterinary use. Nothing here is medical advice. Reviewed by Dr. Langlois, founder of TrueLabs. Related: research peptides in Canada and the COA library.