Peptide Glossary: Research Terminology A–Z

Short, honest definitions of peptide science, pharmacology, and regulatory terms used across this site.

Agonist: A molecule that binds a receptor and activates it, producing a biological response. GLP-1 agonists (e.g., semaglutide) activate the GLP-1 receptor to mimic the gut hormone's effect.
Amino acid: The 20 standard building blocks of proteins and peptides. Peptides are short chains (typically 2–50); proteins are longer. Order and chemistry determine function.
Anagen phase: The active growth phase of a hair follicle. Treatments like minoxidil work partly by extending anagen duration, keeping hairs growing longer before shedding.
Angiogenesis: Formation of new blood vessels from existing ones. Many healing peptides (BPC-157, TB-500) upregulate VEGF/VEGFR2 signaling, a core angiogenic pathway.
Bacteriostatic water: Sterile water with 0.9% benzyl alcohol as preservative. Used to reconstitute lyophilized peptide vials. Preservative inhibits bacterial growth, allowing multi-dose use up to ~28 days.
BDNF: Brain-Derived Neurotrophic Factor — a protein supporting neuron growth, survival, and plasticity. Upregulated by Semax and exercise; central to neuroplasticity research.
Bioavailability: The fraction of an administered dose that reaches systemic circulation unchanged. Oral peptides typically have very low bioavailability (often <1%) because stomach enzymes degrade them — which is why most are injected.
CJC-1295: A synthetic GHRH analog. Two forms: "with DAC" (Drug Affinity Complex, ~6–8 day half-life via albumin binding) and "without DAC" (modified GRF 1-29, ~30 min half-life).
Dermal papilla: Cluster of specialized cells at the base of each hair follicle that controls hair growth cycles. GHK-Cu stimulates dermal papilla cells in vitro.
FDA: United States Food and Drug Administration. "FDA-approved" means a drug passed safety/efficacy review for a specific indication. Most research peptides are not FDA-approved.
GHRH / GHRP: Growth Hormone Releasing Hormone (GHRH) is the hypothalamic peptide that tells the pituitary to release GH. GHRPs (Growth Hormone Releasing Peptides, e.g., ipamorelin) work via the ghrelin receptor instead. Often combined in research protocols.
GLP-1: Glucagon-Like Peptide-1. Gut hormone released after eating; stimulates insulin, suppresses glucagon and appetite. GLP-1 agonists (semaglutide, tirzepatide) treat type 2 diabetes and obesity.
Half-life (t½): Time for a drug's plasma concentration to fall by half. Short half-life (minutes) means frequent dosing; long half-life (days) allows weekly dosing.
IGF-1: Insulin-like Growth Factor 1. Produced mostly by the liver in response to GH; mediates many of GH's anabolic effects. Elevated IGF-1 is a surrogate marker for GH activity.
Intranasal: Administration via the nose. Nasal mucosa offers rapid absorption and can reach the brain via the olfactory route, bypassing first-pass liver metabolism. Used for Semax and Selank.
Lyophilized: Freeze-dried. Most research peptides ship as lyophilized powder in glass vials because dry peptide is far more stable than solution. Requires reconstitution before use.
Nootropic: Loose term for substances claimed to improve cognition, memory, or focus. Evidence ranges from strong (caffeine) to weak/anecdotal (most peptides marketed as nootropics).
Peptide: A short chain of amino acids linked by peptide bonds. Typically 2–50 residues; longer chains are proteins. Peptides act as hormones, neurotransmitters, and signaling molecules.
Pharmacokinetics: What the body does to a drug — absorption, distribution, metabolism, excretion (ADME). Determines dosing schedule. Contrasted with pharmacodynamics (what the drug does to the body).
Pulsatile secretion: Release of a hormone in discrete bursts rather than a steady stream. GH is naturally pulsatile, peaking during deep sleep. Short-acting GHRPs mimic this pattern.
Receptor: A protein that binds a specific ligand (hormone, peptide, drug) and triggers a cellular response. Most peptide drugs target G-protein coupled receptors (GPCRs) on cell surfaces.
Reconstitution: Dissolving lyophilized peptide powder into bacteriostatic or sterile water to create an injectable solution. Proper technique (gentle swirling, not shaking) preserves peptide integrity.
Research chemical: A compound sold "for research use only" — not approved for human consumption. Not a regulatory category with specific standards; often used as a marketing shield for unapproved substances.
Subcutaneous (SC): Injection into the fatty tissue just under the skin. Slower absorption than intramuscular; most GH-releasing peptides and GLP-1 agonists are administered SC.
Tuftsin: A natural tetrapeptide (Thr-Lys-Pro-Arg) with immunomodulatory activity. Selank is a synthetic Tuftsin analog with Pro-Gly-Pro tail for stability.
VEGF: Vascular Endothelial Growth Factor. Signals new blood vessel formation. Upregulated by several healing peptides and by GHK-Cu.
WADA: World Anti-Doping Agency. Maintains the Prohibited List for competitive athletes. Most GH-releasing peptides, BPC-157, and TB-500 are WADA-banned.
Wnt/β-catenin: A cell signaling pathway central to development, regeneration, and hair follicle cycling. GHK-Cu activation of this pathway is one proposed mechanism for its hair and skin effects.