Research peptide product pages, certificates of analysis, and published papers share a vocabulary that is rarely explained. This glossary defines the terms you are most likely to meet, in plain language.
Terms are grouped alphabetically. Where a longer explanation exists elsewhere on the site, we link to it.
A
Acetate salt A common salt form in which a peptide is supplied, with acetate as the counter-ion. Peptides are often converted to acetate form after purification. See also counter-ion and TFA salt.
Agonist A molecule that binds a receptor and activates it, producing a response. A dual agonist activates two receptor types; a triple agonist activates three. See our GLP-1 class comparison for examples.
Amino acid The building block of peptides and proteins. Twenty standard amino acids are encoded by the genetic code; synthetic peptides can also include non-standard or modified amino acids.
Amino acid sequence The order of amino acids in a peptide chain, written from the N-terminus to the C-terminus. The sequence defines a peptide’s identity. It is often written with three-letter codes (Thr-Lys-Pro) or one-letter codes (TKP).
Analog (analogue) A synthetic molecule modeled on a natural one, with deliberate structural changes. Tesamorelin, for example, is described in its FDA label as a GRF analog.
Antagonist A molecule that binds a receptor without activating it, blocking activation by other molecules.
Aseptic technique Laboratory practices that prevent microbial contamination when handling materials, such as working in a clean environment, disinfecting vial stoppers, and using sterile equipment. See reconstituting peptides for laboratory use.
B
Bacteriostatic water Sterile water containing a preservative, typically benzyl alcohol, that inhibits bacterial growth. It is used as a diluent in laboratory settings. Compare sterile water, and see bacteriostatic water vs sterile water.
Batch (lot) A quantity of material produced in one manufacturing run and treated as uniform. A batch number or lot number links a vial to its documentation.
Benzyl alcohol A preservative commonly used in bacteriostatic water.
C
Certificate of Analysis (COA) A document reporting analytical results for a specific batch, typically including identity (mass spectrometry) and purity (HPLC) data. See how to read a COA.
Chromatogram The graph produced by chromatography (such as HPLC), showing detector signal over time. Each peak represents a component; the main peak should correspond to the target peptide.
Counter-ion An ion that pairs with a charged peptide to form a salt. Common counter-ions are acetate and trifluoroacetate (TFA). Counter-ions add mass to the powder without being peptide.
C-terminus The end of a peptide chain with a free carboxyl group (or a modified one, such as an amide). By convention, sequences are written ending at the C-terminus.
D
DAC (Drug Affinity Complex) A chemical modification designed to let a peptide bind albumin in circulation, extending its half-life. The term is most often seen with CJC-1295. See our growth hormone secretagogues overview.
Deletion sequence An impurity in which one or more amino acids are missing from the intended sequence, typically arising during synthesis.
Diluent A liquid used to dissolve or dilute a material, such as bacteriostatic water or sterile water.
E
Endotoxin A component of the outer membrane of certain bacteria that can contaminate laboratory materials. Endotoxin testing is a separate analysis from purity testing.
Excipient An ingredient in a formulation other than the active substance, such as a bulking agent or stabilizer. Many research peptides are supplied without excipients; where excipients are present, they should be stated.
G
GHRH (growth hormone-releasing hormone) A hypothalamic peptide that stimulates the pituitary to synthesize and release growth hormone. Also called growth hormone-releasing factor (GRF or GHRF). GHRH analogs include tesamorelin and CJC-1295.
GHS-R1a (ghrelin receptor) The growth hormone secretagogue receptor, activated by the hormone ghrelin and by ghrelin mimetics such as ipamorelin.
GIP (glucose-dependent insulinotropic polypeptide) An incretin hormone. GIP receptor activity is part of the design of tirzepatide and retatrutide.
GLP-1 (glucagon-like peptide-1) An incretin hormone released from the gut. GLP-1 receptor agonists are a major class of peptide research compounds.
GPCR (G protein-coupled receptor) A large family of cell-surface receptors that signal through G proteins. The GLP-1, GIP, glucagon, and GHRH receptors are all GPCRs.
H
Half-life The time it takes for the amount or concentration of a substance to fall by half. It may refer to half-life in circulation (pharmacokinetic half-life) or to stability in storage, so context matters.
HPLC (high-performance liquid chromatography) An analytical technique that separates the components of a sample as it passes through a packed column under pressure. On a COA, HPLC is used to estimate purity. See peptide purity, HPLC, and mass spec.
Hygroscopic Readily absorbing moisture from the air. Many lyophilized peptides are hygroscopic, which is why vials should reach room temperature before opening.
I
IGF-1 (insulin-like growth factor 1) A hormone produced mainly in the liver in response to growth hormone. It is frequently measured as an endpoint in growth hormone secretagogue studies. IGF-1 LR3 is a modified analog.
In vitro Literally “in glass”: research conducted outside a living organism, such as in cell cultures or test tubes.
In vivo Research conducted within a living organism, such as an animal model.
Investigational Describes a compound that is being studied in clinical trials but has not been approved by a regulatory authority. Retatrutide is an example.
L
Lyophilization Freeze-drying. The material is frozen, then placed under vacuum so ice sublimates directly to vapor, leaving a dry powder or cake. See lyophilized peptides explained.
Lyophilized cake The solid, often porous, mass left at the bottom of a vial after lyophilization. Its appearance can vary between batches without indicating a problem.
M
Mass spectrometry (MS) An analytical technique that measures the mass-to-charge ratio of ions. On a COA, it is used to confirm identity by comparing the observed molecular mass with the expected mass.
Mimetic A molecule that imitates the action of another. A ghrelin mimetic activates the ghrelin receptor.
Molecular weight (MW) The mass of one molecule, usually expressed in daltons (Da) or grams per mole. For peptides, the expected MW is calculated from the sequence and compared against mass spectrometry results.
N
Net peptide content The percentage of a powder’s total mass that is peptide, as opposed to counter-ions, residual water, and other non-peptide material. It is distinct from purity.
N-terminus The end of a peptide chain with a free amino group. Sequences are written starting from the N-terminus.
P
Peptide A chain of amino acids joined by peptide bonds. Chains up to roughly 50 amino acids are conventionally called peptides; longer, folded chains are usually called proteins. See what are research peptides?.
Peptide bond The covalent amide bond linking the carboxyl group of one amino acid to the amino group of the next, releasing a molecule of water.
Pharmacodynamics (PD) The study of what a substance does to a biological system, such as receptor activation or changes in hormone levels.
Pharmacokinetics (PK) The study of how a biological system handles a substance over time: absorption, distribution, metabolism, and elimination.
Preclinical Research conducted before human trials, including in vitro and animal studies.
Purity The proportion of a sample that is the intended peptide, usually estimated by HPLC peak area. A purity figure should always be traceable to a batch-specific report.
R
Receptor A protein, usually on a cell surface, that binds a specific signaling molecule and triggers a cellular response.
Reconstitution Dissolving a lyophilized material in a diluent to form a solution for laboratory use. See reconstituting peptides for laboratory use.
Research use only (RUO) A designation meaning a material is supplied for laboratory research and is not a drug, food, cosmetic, or dietary supplement, and not for human or veterinary use. The phrase originates in FDA’s labeling rules for in vitro diagnostic products (21 CFR 809.10). See our US regulatory overview and research-use policy.
Retention time In chromatography, the time at which a component elutes from the column and appears as a peak. It helps distinguish the target peptide from impurities.
S
Salt form The form in which a charged peptide is isolated, paired with a counter-ion (for example, acetate or TFA).
Secretagogue A substance that causes another substance to be secreted. A growth hormone secretagogue stimulates growth hormone release.
Solid-phase peptide synthesis (SPPS) The standard method for making synthetic peptides, in which amino acids are added one at a time to a growing chain anchored to a solid resin. It was introduced by R. B. Merrifield in 1963.
Stability A material’s ability to retain its identity and purity over time under given storage conditions. See the peptide storage guide.
Sterile water Water that has been sterilized and contains no preservative. Compare bacteriostatic water.
T
TFA salt (trifluoroacetate) A salt form that results when trifluoroacetic acid is used during peptide cleavage and purification. Some suppliers exchange TFA for acetate.
Truncated sequence An impurity in which the peptide chain stopped growing before completion during synthesis.
W
WADA Prohibited List The World Anti-Doping Agency’s annual list of substances and methods prohibited in sport. Several research peptides appear on it.
Keep Learning
- Start with what are research peptides?
- Learn to evaluate documentation with how to read a COA
- Use our checklist for vetting a research peptide supplier
- Browse the research compound library, or shop research peptides and research supplies
- Read about our standards on the Quality page
