Reference
Peptide Research Glossary
Definitions of key terms used in peptide research, administration, and pharmacology. Entries include Schema.org DefinedTerm structured data to improve search engine and AI citation coverage.
Agonist
A compound that binds to a receptor and activates it, producing a biological response. Contrasts with an antagonist, which binds without producing activation.
Amino acid
The molecular building blocks of peptides and proteins. Peptides consist of chains of two or more amino acids joined by peptide bonds.
Angiogenesis
The formation of new blood vessels from existing vasculature. Investigated as a mechanism through which compounds such as BPC-157 and TB-500 may promote tissue repair.
See also: Angiogenesis & Tissue RepairAntagonist
A compound that binds to a receptor and blocks its activation without producing a response itself.
Bacteriostatic water (BAC water)
Sterile water for injection containing 0.9% benzyl alcohol (9 mg/ml). The benzyl alcohol inhibits bacterial growth, allowing multi-dose use of reconstituted peptide vials over 28–30 days. The standard diluent for research peptide reconstitution.
See also: Bacteriostatic Water GuideBDNF (Brain-derived neurotrophic factor)
A protein that promotes the growth, differentiation, and survival of neurons. Upregulated by nootropic peptides including Semax. A key target in neuroplasticity and neuroprotection research.
Bioavailability
The proportion of an administered compound that reaches systemic circulation in an active form. Most peptides have very low oral bioavailability due to proteolytic degradation in the gastrointestinal tract, which is why injectable administration is standard.
Collagen
The most abundant structural protein in the human body, comprising approximately 30% of total protein mass. Collagen provides tensile strength to skin, tendons, ligaments, cartilage, and bone. Type I collagen is the most prevalent form and the primary target of skin-focused peptide research. Its production declines progressively from the third decade of life.
See also: Collagen SynthesisConcentration
The amount of a dissolved substance per unit volume of solution. For reconstituted peptides, typically expressed in micrograms per millilitre (mcg/ml). Concentration determines the volume of solution required per dose.
See also: Reconstitution GuideGHRPs (Growth Hormone Releasing Peptides)
A class of synthetic peptides that stimulate pituitary growth hormone secretion by binding the ghrelin receptor (GHS-R1a). Includes Ipamorelin, GHRP-2, and GHRP-6. Act synergistically with GHRH analogues.
See also: GHRPs · Growth Hormone SecretionGHRH (Growth Hormone Releasing Hormone)
A hypothalamic peptide that binds the GHRH receptor on pituitary somatotrophs, stimulating pulsatile growth hormone release. CJC-1295 and Sermorelin are synthetic GHRH analogues.
See also: GHRH AnaloguesGIP (Glucose-dependent insulinotropic polypeptide)
An incretin hormone secreted by K-cells in the small intestine in response to food intake. Activates the GIP receptor to potentiate insulin secretion and modulate adipocyte function. A secondary target of tirzepatide and retatrutide alongside GLP-1.
GLP-1 (Glucagon-like peptide-1)
An incretin hormone secreted by intestinal L-cells in response to food intake. Acts at the GLP-1 receptor to stimulate insulin secretion, suppress glucagon, slow gastric emptying, and promote satiety. The primary target of semaglutide, tirzepatide, and retatrutide.
See also: GLP-1 Receptor AgonismGrowth Hormone (GH)
A 191-amino-acid peptide hormone secreted by somatotroph cells of the anterior pituitary gland. Regulates growth, body composition, cell reproduction, and metabolism. Released in pulsatile fashion, primarily during sleep; stimulated by GHRH and ghrelin, inhibited by somatostatin and IGF-1 feedback. Downstream effects are largely mediated through IGF-1 produced in the liver.
See also: Growth Hormone SecretionHalf-life
The time required for the plasma concentration of a compound to decrease by 50%. Determines dosing frequency: compounds with short half-lives (minutes to hours) require more frequent administration than those with long half-lives (days). Semaglutide's ~7-day half-life enables once-weekly dosing; native GLP-1's 2-minute half-life makes it impractical as a drug without modification.
IGF-1 (Insulin-Like Growth Factor 1)
A peptide hormone produced primarily by the liver in response to growth hormone stimulation. Mediates many of GH's anabolic and growth-promoting effects in peripheral tissues — including protein synthesis, cell proliferation, and fat metabolism. Serum IGF-1 levels are widely used as a biomarker to assess GH axis activity in research contexts because they are more stable than pulsatile GH measurements.
Immunomodulation
The adjustment or regulation of the immune response, either enhancing or suppressing specific immune activity. Thymosin peptides — including TB-500 (Thymosin Beta-4) and Thymosin Alpha-1 — have been researched for immunomodulatory properties, particularly in wound healing and immune reconstitution contexts.
See also: Thymosin PeptidesIntramuscular (IM)
Injection directly into muscle tissue. Produces more rapid absorption than subcutaneous injection for some compounds due to the vascular supply in muscle.
Intranasal
Administration of a compound via the nasal mucosa. Used for peptides such as Semax and Selank, enabling CNS delivery through the olfactory pathway with relatively rapid onset and without systemic injection.
Lyophilization
A freeze-drying process in which water is removed from a compound under vacuum at low temperature, producing a stable powder. Lyophilized peptides have extended shelf life compared to solutions and are stable at room temperature for transport. Requires reconstitution with a sterile solvent before administration.
See also: Storage GuideMicrogram (mcg / µg)
One millionth of a gram (0.000001 g). The standard unit for peptide dosing. 1,000 mcg = 1 mg.
Milligram (mg)
One thousandth of a gram (0.001 g). Used for vial sizes (e.g. a 5 mg vial of BPC-157) and for dosing larger peptides such as GLP-1 agonists.
NAD+ (Nicotinamide Adenine Dinucleotide)
A coenzyme found in all living cells, essential for mitochondrial energy metabolism (oxidative phosphorylation) and as a substrate for sirtuins and PARP enzymes involved in DNA repair and gene expression regulation. NAD+ levels decline with age; research has investigated NAD+ supplementation as a longevity and metabolic health intervention. Classified on this site as a research compound rather than a classical peptide.
See also: NAD+ Profile · Mitochondrial PeptidesOff-label
The use of an approved pharmaceutical for a purpose, population, or dose not specified in its approved labelling. Semaglutide and tirzepatide, for example, are sometimes used in research contexts outside their approved indications.
Peptide
A short chain of amino acids, typically defined as chains of 2–50 residues. Distinguished from proteins, which are longer polypeptide chains. Peptides can act as hormones, signalling molecules, enzymes, and research compounds. The boundary between peptide and protein is conventional rather than sharp.
Peptide bond
The covalent chemical bond formed between the carboxyl group of one amino acid and the amino group of another, releasing water (a condensation reaction). The fundamental structural linkage in all peptides and proteins.
Phase 2 trial
A clinical trial phase in which a compound is tested in a larger group of participants (typically dozens to hundreds) to assess efficacy, optimal dosing, and side effect profile. Follows Phase 1 safety testing. Retatrutide is currently in Phase 2 development.
Receptor
A protein located on a cell surface or within a cell that binds specific molecules (ligands) and initiates a cellular signalling response. Most peptides exert their effects by binding G protein-coupled receptors (GPCRs) or receptor tyrosine kinases (RTKs).
Reconstitution
The process of dissolving a lyophilized peptide powder in a liquid (typically bacteriostatic water) to produce an injectable solution. Concentration is determined by the volume of liquid added relative to the mass of peptide in the vial.
See also: Reconstitution GuideResearch chemical
A substance studied for potential therapeutic or biological activity that has not received regulatory approval for human therapeutic use. Legal status and availability varies by jurisdiction. Distinct from approved pharmaceuticals such as semaglutide and tirzepatide.
Secretagogue
A substance that stimulates secretion of another substance. In peptide research, most commonly refers to compounds that stimulate growth hormone secretion from the pituitary gland. GHRPs are classified as growth hormone secretagogues.
Sterile water
Water purified and sterilized for injection but containing no preservative. Appropriate for single-dose reconstitution only; once a vial is punctured, sterile water provides no protection against bacterial contamination. Bacteriostatic water is preferred for multi-dose research use.
Subcutaneous (SubQ)
Injection into the tissue layer immediately beneath the skin (the subcutaneous adipose layer). The most common administration route for research peptides. Common injection sites include the abdomen, outer thigh, and upper arm. Absorption is generally slower than intramuscular injection but more consistent.
Supraphysiological
Exceeding the concentrations or activity levels produced naturally by the body under normal physiological conditions. Relevant when describing hormone or peptide levels that are higher than the body's endogenous output — a distinction used in research literature when interpreting dose-response relationships.
Telomerase
An enzyme that adds DNA sequence repeats (TTAGGG in humans) to the ends of chromosomes (telomeres), counteracting the telomere shortening that occurs during each cell division. Telomere shortening is associated with cellular senescence and aging. Research has investigated Epitalon for its potential to activate telomerase expression.
See also: Telomerase Activation · Epitalon ProfileU-100
A syringe calibration standard in which 1 ml of solution equals 100 units. U-100 insulin syringes are the standard tool for peptide injection. On a U-100 syringe, 10 units = 0.10 ml; 50 units = 0.50 ml; 100 units = 1.00 ml.
See also: Syringe GuideU-40
A syringe calibration standard in which 1 ml equals 40 units. Less common than U-100; used primarily in veterinary contexts. Confusion between U-40 and U-100 syringes will produce significant dosing errors — always verify syringe type before calculating volumes.
Vial
A small sealed glass or plastic container used to store lyophilized peptide powder or reconstituted peptide solution. Research peptides are commonly supplied in 2–10 mg lyophilized vials sealed under inert gas.