Glossary

Plain-language definitions of peptide science and analytical-testing terminology used across the site.

5

503A Category 2: FDA designation for substances nominated for compounding under Section 503A but flagged with significant safety concerns — effectively do-not-compound pending review.

A

AHI: Apnea-Hypopnea Index. Events per hour during sleep. Primary endpoint in the SURMOUNT-OSA tirzepatide trial in obstructive sleep apnea.
Agonist: A compound that binds a receptor and activates its downstream signaling. Semaglutide is a GLP-1 receptor agonist.
Amino acid: Organic compound containing both amine (-NH2) and carboxylic acid (-COOH) groups. The building blocks of peptides and proteins.
Antagonist: A compound that binds a receptor and blocks its activation, without producing a signaling response itself.
Assay: An analytical procedure that measures the concentration, identity, or activity of a substance — in our context, a peptide sample.

B

Batch: A specific quantity of material produced in one run under defined conditions. Analytical testing is performed on a per-batch basis.
Bioavailability: The fraction of an administered dose that reaches systemic circulation unchanged. Most injectable peptides have very low oral bioavailability.
Blind purchase: A sample-acquisition method in which the supplier is not informed that the purchaser is a testing organization. Eliminates the possibility of a cherry-picked batch being sent.

C

C-terminus: The end of a peptide with a free carboxyl group. The last residue listed when writing a peptide sequence.
COA: Certificate of Analysis. A document issued by a testing lab reporting the analytical characteristics of a specific batch of material.
Compounding pharmacy: Facility authorized to combine or alter FDA-approved drugs to meet individual patient needs. Section 503A covers traditional compounding; 503B covers outsourcing facilities.

D

DEA Scheduled: Substances controlled under the US Controlled Substances Act. Most research peptides are not DEA scheduled (exception: dermorphin and other potent mu-opioid peptides).
DPP-4: Dipeptidyl peptidase-4. Enzyme that degrades native GLP-1. Modifications at position 8 (e.g., Aib substitution in semaglutide) confer DPP-4 resistance.
Disulfide bond: Covalent bond between two sulfur atoms from cysteine side chains. Stabilizes peptide three-dimensional structure (e.g., oxytocin, insulin).

F

FDA Shortage List: Official FDA registry of drugs in supply shortage. During active shortage, compounding of copies is permitted under specific conditions. Semaglutide and tirzepatide were both resolved off this list in October 2024.
Fmoc SPPS: Fluorenylmethoxycarbonyl Solid-Phase Peptide Synthesis. The standard modern method for synthesizing peptides in a laboratory setting.

G

GHRH: Growth hormone-releasing hormone. Endogenous 44-amino-acid hypothalamic peptide that stimulates pituitary growth hormone release. Parent molecule of sermorelin and tesamorelin.
GIP: Glucose-dependent insulinotropic polypeptide. A second incretin hormone alongside GLP-1. Tirzepatide is a dual GIP/GLP-1 agonist.
GLP-1: Glucagon-like peptide-1. An incretin hormone that stimulates glucose-dependent insulin release and suppresses glucagon. The therapeutic target of semaglutide and related drugs.
GPCR: G-protein-coupled receptor. Seven-transmembrane cell-surface receptors. Most peptide hormone receptors (GLP-1R, GHRH-R, GHS-R1a, melanocortin receptors) are GPCRs.
Ghrelin: The "hunger hormone" — a 28-amino-acid peptide that binds GHS-R1a receptors. Ipamorelin and MK-677 mimic ghrelin to stimulate GH release.

H

HPLC: High-performance liquid chromatography. Separates components in a mixture to measure purity — the primary method for peptide purity testing.
Half-life: Time for plasma concentration of a substance to fall by half. Determines dosing frequency. Semaglutide's ~165-hour half-life enables weekly dosing.

I

IGF-1: Insulin-like growth factor 1. Downstream mediator of most growth hormone effects. Elevation by GH secretagogues is typically measured to assess biological response.

L

LAL assay: Limulus amebocyte lysate assay. Detects bacterial endotoxin contamination. Critical for injectable research peptides.
LC-MS: Liquid chromatography – mass spectrometry. Separates then identifies compounds by mass. Confirms that a peptide is what its label claims.
Lot number: A unique identifier assigned to a specific batch. Critical for traceability when testing or recalling material.

M

MALDI-TOF: Matrix-assisted laser desorption ionization – time of flight mass spectrometry. Common peptide identity confirmation method.
MASH: Metabolic dysfunction-associated steatohepatitis. The inflammatory subset of MASLD. Formerly NASH. Target indication for semaglutide and retatrutide.
MASLD: Metabolic dysfunction-associated steatotic liver disease. Formerly NAFLD. An active research indication for GLP-1 agonists and tesamorelin.
MEN2: Multiple Endocrine Neoplasia type 2. An inherited syndrome predisposing to medullary thyroid carcinoma. Contraindication for GLP-1 drugs.
MTC: Medullary thyroid carcinoma. A rare thyroid cancer arising from C-cells. GLP-1 drugs carry boxed warnings for MTC based on rodent findings.
Meta-analysis: Statistical synthesis of multiple independent studies. Can reveal or obscure true effects depending on methodology and study quality.

N

N-terminus: The end of a peptide with a free amino group. The first residue listed when writing a peptide sequence.

P

Peptide: A short chain of amino acids linked by peptide bonds. Typically fewer than 50 residues; longer chains are called proteins.
Peptide bond: Covalent bond formed between the carboxyl group of one amino acid and the amino group of another, releasing water. The fundamental linkage of peptides.
Pharmacodynamics: What a drug does to the body: receptor binding, downstream signaling, physiological effect. Determines efficacy.
Pharmacokinetics: What the body does to a drug: absorption, distribution, metabolism, excretion. Determines dosing schedule.
Phase 1 trial: First-in-human study. Small sample (20-80 volunteers), focused on safety, tolerability, and pharmacokinetics. Not powered for efficacy.
Phase 2 trial: Early efficacy and dose-finding study. Typically 100-500 participants in the target population. Informs Phase 3 design.
Phase 3 trial: Pivotal efficacy study for regulatory approval. Hundreds to thousands of participants across multiple sites. Used as basis for FDA approval.
Portable Text: A JSON-based rich-text format used by Sanity CMS to store structured editorial content. Relevant context for how Open Assay stores peptide pages.
Pulsatile release: Periodic burst-release pattern of endogenous hormones (e.g., GH). Short-half-life GHRH analogs preserve pulsatility; long-acting CJC-1295+DAC produces sustained non-pulsatile elevation.

R

RCT: Randomized controlled trial. Participants randomly assigned to treatment or control. The gold standard for establishing causal efficacy.
Reference standard: A highly characterized material of known composition and purity used as a calibration benchmark in analytical testing. Sometimes called “primary reference material.”
Research use only (RUO): A product label indicating that a material is intended for laboratory research and not for human consumption, diagnostic, or therapeutic use.

S

Single-lab dominance: Research area where most publications come from one laboratory or research group. A flag for concern because independent replication is essential in science.
Systematic review: Structured literature review with pre-specified inclusion criteria. Cochrane systematic reviews are a common high-rigor reference.

V

VEGFR2: Vascular endothelial growth factor receptor 2. A tyrosine kinase receptor driving angiogenesis. Implicated in proposed mechanisms of BPC-157 and TB-500.

W

WADA: World Anti-Doping Agency. Maintains the Prohibited List. Many research peptides (TB-500, MK-677, GH secretagogues) are WADA-banned for competitive athletes.