Peptide Glossary

Plain-language definitions for peptide, pharmacology, and research terms used across this site. 77 terms, alphabetically organized.

A

ACTH (Adrenocorticotropic Hormone): A pituitary hormone that stimulates the adrenal cortex to produce cortisol. Some melanocortin peptides share structural similarity with ACTH and may exert effects through overlapping receptor pathways.
Alpha-MSH (Alpha-Melanocyte-Stimulating Hormone): An endogenous melanocortin peptide derived from POMC. It acts on MC1R–MC5R receptors, influencing pigmentation, inflammation, appetite, and sexual function. Synthetic analogs include Melanotan-II and PT-141.
AMPK (AMP-Activated Protein Kinase): A cellular energy sensor that promotes fat oxidation, mitochondrial biogenesis, and glucose uptake when activated. MOTS-c is reported to activate AMPK, which underpins its proposed metabolic effects.→ MOTS-c
AUC (Area Under the Curve): A pharmacokinetic measure of total drug exposure over time, calculated from a concentration–time plot. Higher AUC generally indicates greater systemic exposure.

B

Bacteriostatic Water: Sterile water containing 0.9% benzyl alcohol, which inhibits microbial growth. It is the standard diluent for reconstituting injectable peptides because it preserves multi-dose vials for weeks at refrigerator temperature.
Bioavailability: The fraction of an administered dose that reaches systemic circulation unchanged. Subcutaneous injection typically yields higher bioavailability for peptides than oral administration, because the gut and liver degrade most peptide bonds before absorption.
BPC-157: Body Protection Compound-157, a synthetic pentadecapeptide derived from a gastric protein sequence. Studied in animal models for tissue regeneration, gut healing, and tendon repair. Not FDA-approved; classified as a research chemical.→ BPC-157 profile

C

Case Report: A detailed description of a single patient's presentation, treatment, and outcome. It is the lowest tier of clinical evidence but can flag unexpected effects worth studying further.
CJC-1295: A synthetic GHRH analog with an extended half-life due to drug-affinity technology (DAC). Increases GH and IGF-1 levels and is sometimes stacked with GHRP peptides like ipamorelin. Not FDA-approved.→ CJC-1295 profile
Cmax: The maximum plasma concentration of a compound reached after administration. A key pharmacokinetic parameter for assessing peak exposure.
Compounded Medication: A drug prepared by a licensed pharmacy for an individual patient, often when a commercially manufactured version is unavailable or unsuitable. Compounded peptides are not FDA-approved drug products and are not subject to the same pre-market review.
Contraindication: A condition or factor that makes a particular treatment inadvisable. For example, active malignancy is a contraindication for GH-stimulating peptides due to theoretical concerns about tumor growth.

D

DailyMed: The official FDA labeling database (dailymed.nlm.nih.gov) that provides current prescribing information, including indications, contraindications, and warnings, for all approved drug products in the US.
DSIP (Delta Sleep-Inducing Peptide): A neuropeptide originally identified in the venous blood of sleeping rabbits. Studied for effects on sleep architecture, stress response, and cortisol regulation. Evidence is primarily preclinical.→ DSIP profile

E

Epitalon (Epithalon): A synthetic tetrapeptide (Ala-Glu-Asp-Gly) developed in Russia. Proposed to stimulate telomerase, extend telomere length, and regulate melatonin. Evidence is mostly preclinical; no FDA approval.→ Epitalon profile
Evidence Tier: A classification system for research quality. Tier 1 = FDA/regulatory approval; Tier 2 = Phase 3 RCTs; Tier 3 = Phase 1–2 or preclinical trials; Tier 4 = Observational/case reports; Tier 5 = Anecdotal only. Pepteligence labels each peptide with its current tier.

F

FDA Approval: Formal authorization from the US Food and Drug Administration that a drug is safe and effective for a specific indicated use, based on clinical trial data reviewed through the NDA or BLA process.
Frequency (Dosing): How often a peptide is administered — for example, once daily, twice daily, or pulsatile (timed around sleep or fasting). Frequency affects both efficacy and receptor desensitization for secretagogue peptides.

G

GHK-Cu (Copper Peptide): A tripeptide (Gly-His-Lys) bound to copper. Found naturally in human plasma and studied for wound healing, collagen synthesis, and anti-inflammatory effects. Used topically in cosmetics and investigated in preclinical research.→ GHK-Cu profile
GHRH (Growth Hormone-Releasing Hormone): The hypothalamic hormone that signals the pituitary to release growth hormone. GHRH analogs like CJC-1295, sermorelin, and tesamorelin mimic this signal to increase GH and downstream IGF-1 levels.→ CJC-1295, Sermorelin, Tesamorelin
GH Secretagogue: Any compound that stimulates the release of growth hormone. Includes GHRH analogs, ghrelin mimetics (GHRPs), and GHRP/GHRH combination stacks like ipamorelin + CJC-1295.→ Ipamorelin, Hexarelin, MK-677
GLP-1 (Glucagon-Like Peptide-1): An incretin hormone released by gut L-cells after eating. It stimulates insulin secretion, suppresses glucagon, slows gastric emptying, and reduces appetite. GLP-1 receptor agonists like semaglutide and tirzepatide are FDA-approved for type 2 diabetes and obesity.→ Semaglutide, Tirzepatide
GnRH (Gonadotropin-Releasing Hormone): A hypothalamic decapeptide that triggers pituitary release of LH and FSH, which in turn regulate sex hormone production. Kisspeptin acts upstream of GnRH neurons to control GnRH pulsatility.→ Kisspeptin

H

Half-Life: The time it takes for the plasma concentration of a compound to fall by 50%. Short half-lives (minutes) require more frequent dosing; modified peptides (e.g., CJC-1295 DAC) are engineered for extended half-lives measured in days.
HbA1c (Glycated Hemoglobin): A blood marker reflecting average plasma glucose over the preceding 2–3 months. Used as a primary endpoint in diabetes trials. GLP-1 agonists such as semaglutide and tirzepatide produce clinically significant HbA1c reductions.→ Semaglutide, Tirzepatide
Hexarelin: A synthetic GHRP (growth hormone-releasing peptide) that stimulates GH release more potently than most peptides in its class, but also elevates cortisol and prolactin. Preclinical and early clinical evidence for cardioprotective effects.→ Hexarelin profile
HPG Axis (Hypothalamic–Pituitary–Gonadal Axis): The hormonal feedback loop linking the hypothalamus (GnRH), pituitary (LH, FSH), and gonads (testosterone, estradiol, progesterone). Kisspeptin is a key upstream regulator of this axis.→ Kisspeptin

I

IGF-1 (Insulin-Like Growth Factor-1): A liver-derived hormone secreted in response to growth hormone. Mediates many of GH's anabolic effects on muscle, bone, and connective tissue. Elevated by GHRH analogs and GH secretagogues; used as a biomarker of GH axis activity.
Indication: The specific disease or condition for which a drug is approved and for which its use is considered medically appropriate based on clinical evidence.
Intramuscular (IM): A route of administration in which a compound is injected into muscle tissue. Less common than subcutaneous for most peptides, but used for some compounds due to slower absorption profiles.
Intranasal: Delivery via the nasal mucosa, which provides direct access to the bloodstream and potentially to the brain via the olfactory pathway. Selank and Semax are studied in intranasal form.→ Selank, Semax
Ipamorelin: A selective GHRP that stimulates GH release with minimal effect on cortisol or prolactin, making it one of the cleaner GH secretagogues. Often stacked with CJC-1295.→ Ipamorelin profile
IU (International Unit): A unit of measurement for biologics and hormones standardized by their biological activity rather than mass. Growth hormone is commonly dosed in IU. 1 mg of recombinant GH ≈ 3 IU, though conversion varies by product.

K

Kisspeptin: A hypothalamic neuropeptide encoded by the KISS1 gene that activates GnRH neurons and regulates the HPG axis. Used in clinical research to probe fertility disorders and studied for potential use in hypogonadism.→ Kisspeptin profile
KNDy System (Kisspeptin–Neurokinin B–Dynorphin): A tripartite hypothalamic neuronal system that governs pulsatile GnRH secretion and thus the entire HPG axis. KNDy neurons integrate metabolic and hormonal signals to modulate reproductive function.→ Kisspeptin
KPV: A tripeptide (Lys-Pro-Val) fragment of alpha-MSH. Studied for anti-inflammatory and gut-protective effects in animal models of IBD. Proposed to act via MC1R in gut epithelium. No human clinical trials to date.→ KPV profile

L

LH (Luteinizing Hormone): A pituitary gonadotropin that triggers testosterone production in males and ovulation in females. Regulated by pulsatile GnRH from the hypothalamus, which is itself gated by kisspeptin.
Lyophilized: Freeze-dried. Most injectable peptides are shipped as lyophilized (dry) powder to preserve stability. Before use, they must be reconstituted with bacteriostatic water or sterile water.

M

MC1R / Melanocortin Receptors: A family of G protein-coupled receptors (MC1R–MC5R) that bind melanocortin peptides including alpha-MSH and ACTH. MC1R governs pigmentation; MC3R/MC4R regulate energy balance and sexual function; MC4R is the primary target of PT-141.
Meta-Analysis: A statistical technique that pools results from multiple independent studies to produce a more precise overall estimate of an effect. Higher-quality than any individual trial when conducted rigorously.
Mechanism of Action: How a drug or peptide produces its biological effect at the molecular or cellular level — e.g., receptor binding, enzyme inhibition, or gene expression modulation.
Mitochondrial-Derived Peptide (MDP): A class of short peptides encoded in mitochondrial DNA that regulate metabolism, stress response, and cell survival. MOTS-c and humanin are the best-characterized MDPs.→ MOTS-c
MK-677 (Ibutamoren): An orally active, non-peptide ghrelin mimetic that increases GH and IGF-1. Technically a small molecule rather than a peptide. Under clinical investigation for muscle wasting and GH deficiency. Not FDA-approved for general use.→ MK-677 profile
MOTS-c: A mitochondrial-derived peptide that activates AMPK and regulates nuclear gene expression related to metabolism. Studied for effects on insulin sensitivity, exercise capacity, and longevity in animal models.→ MOTS-c profile

N

NDA (New Drug Application): The formal process through which a drug sponsor submits clinical trial data to the FDA requesting approval to market a new pharmaceutical in the United States.

O

Observational Study: A study in which researchers observe outcomes without assigning interventions. Includes cohort studies and case-control studies. Useful for detecting associations but cannot establish causation.
Off-Label: Use of an FDA-approved drug for an indication, population, or dose not covered by its approved labeling. Common in medicine; physicians may prescribe off-label, but manufacturers cannot promote it.

P

Peer Review: Evaluation of a scientific manuscript by independent experts in the field before publication. Peer review is a quality filter but does not guarantee correctness or reproducibility.
Phase 1 Trial: The first stage of human clinical testing, focused primarily on safety, tolerability, and pharmacokinetics in a small group (typically 20–80 subjects), often healthy volunteers.
Phase 2 Trial: A clinical trial evaluating preliminary efficacy and optimal dosing in a larger group (typically 100–300 subjects) with the target disease or condition.
Phase 3 Trial: A large-scale clinical trial (typically 300–3,000+ subjects) comparing a new treatment against a placebo or standard of care to establish efficacy and safety for regulatory submission.
Preclinical: Research conducted in cells (in vitro) or animals (in vivo) before human trials begin. Promising preclinical results frequently fail to replicate in humans; this is a common limitation of many peptide claims.
Pulsatile Dosing: Administering a compound in discrete bursts timed to mimic the body's natural hormone secretion rhythm. GH secretagogues are often dosed pulsatilely (e.g., before sleep or after fasting) to prevent receptor desensitization.

R

RCT (Randomized Controlled Trial): A study design in which participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for establishing causal efficacy of a medical intervention.
Reconstitution: The process of dissolving lyophilized peptide powder into a liquid diluent (usually bacteriostatic water) before injection. Proper technique — slow injection down the vial wall, no shaking — preserves peptide integrity.
Regulatory Status: The legal classification of a compound in a given jurisdiction. For peptides, this typically ranges from FDA-approved (e.g., semaglutide, tesamorelin) to research chemical to controlled substance.
Research Chemical: A substance sold legally for research purposes but not approved for human use. Many peptides (BPC-157, TB-500, Epitalon) circulate in this category. Quality, purity, and safety are not regulated by the FDA.
Route of Administration: How a compound enters the body: subcutaneous injection, intramuscular injection, intranasal spray, oral ingestion, or topical application. Route affects absorption speed, bioavailability, and convenience.
RxNorm: A standardized nomenclature system for clinical drugs maintained by the National Library of Medicine. Assigns unique concept identifiers (RxCUI) to drugs, enabling consistent data exchange across health IT systems.

S

Selank: A synthetic heptapeptide analog of tuftsin developed in Russia. Studied for anxiolytic, nootropic, and immunomodulatory effects, primarily via intranasal administration. Evidence is largely preclinical or from small Russian clinical studies.→ Selank profile
Semaglutide: A GLP-1 receptor agonist (Ozempic, Wegovy, Rybelsus) FDA-approved for type 2 diabetes and chronic weight management. One of the most extensively studied peptide drugs with large Phase 3 trial data.→ Semaglutide profile
Semax: A synthetic analog of ACTH(4-7) developed in Russia. Proposed to increase BDNF and improve cognitive function, particularly under stress. Administered intranasally. Preclinical and limited clinical data.→ Semax profile
Sermorelin: A GHRH analog (first 29 amino acids of endogenous GHRH) that was FDA-approved for pediatric GH deficiency and is widely compounded for adult GH support. Short half-life requires daily dosing.→ Sermorelin profile
SPL (Structured Product Labeling): An FDA-standard XML format for drug labeling submitted via DailyMed. SPL documents contain the full prescribing information including indications, warnings, and clinical pharmacology.
Stack: A combination of two or more peptides or compounds used together for synergistic effect. Common examples include ipamorelin + CJC-1295 (GH axis), BPC-157 + TB-500 (tissue repair), and semaglutide + tirzepatide comparison.
Subcutaneous (SubQ): Injected into the fatty tissue just beneath the skin, typically using a short insulin-gauge needle. The most common route for most injectable research peptides and most GLP-1 agonists.
Systematic Review: A structured synthesis of all available evidence on a specific research question, following a predefined protocol to minimize bias. Higher quality than a narrative review; often paired with a meta-analysis.
Syringe Gauge: The outer diameter of a needle; higher gauge = thinner needle. Insulin syringes (28–31 gauge) are standard for subcutaneous peptide injections because they minimize injection-site pain.

T

TB-500 (Thymosin Beta-4 Fragment): A synthetic peptide fragment of thymosin beta-4, an endogenous protein involved in actin regulation and wound healing. Studied in animal models for tissue repair, angiogenesis, and inflammation reduction.→ TB-500 profile
Telomerase: An enzyme that extends telomeres — the protective caps on chromosomes — potentially slowing cellular aging. Epitalon is proposed to upregulate telomerase activity, though human evidence is very limited.→ Epitalon
Tesamorelin: A GHRH analog (Egrifta) FDA-approved for HIV-associated lipodystrophy. Has a stronger evidence base than most GHRH analogs due to large RCTs, but its use outside this indication is off-label.→ Tesamorelin profile
Thymosin Alpha-1 (Tα1): A thymic peptide that modulates innate and adaptive immunity. Approved in some countries for hepatitis B/C and as an adjuvant for cancer vaccines. Studied for post-viral immune support.→ Thymosin Alpha-1 profile
Tirzepatide: A dual GIP/GLP-1 receptor agonist (Mounjaro, Zepbound) FDA-approved for type 2 diabetes and obesity. Produces larger weight loss than single-agonist GLP-1 drugs in head-to-head trials.→ Tirzepatide profile
Tmax: The time after administration at which plasma concentration of a compound reaches its peak (Cmax). Important for timing peptide injections relative to sleep, exercise, or meals.

V

VEGF (Vascular Endothelial Growth Factor): A signaling protein that promotes angiogenesis — the formation of new blood vessels. TB-500 and GHK-Cu are proposed to upregulate VEGF expression, which may contribute to their wound-healing effects.→ TB-500, GHK-Cu

W

WADA (World Anti-Doping Agency): The international body that maintains the Prohibited List used in competitive sport. Many GH-axis peptides (CJC-1295, ipamorelin, sermorelin, hexarelin, GHRP-6, tesamorelin) are banned in and out of competition.→ CJC-1295, Ipamorelin
Warning (Drug Label): A section of FDA prescribing information that describes serious or life-threatening risks. Boxed warnings (the strongest type) require a prominently boxed notice and appear on GLP-1 agonist labels for thyroid C-cell tumor risk in rodent studies.

Disclaimer: This glossary is for research and educational purposes only. It does not constitute medical advice. Consult a licensed physician before using any peptide or compound.