Peptide Glossary

Over 249 terms covering peptide names, pharmacology, administration, chemistry, conditions, equipment, and regulations. Each peptide name links to its full research profile.

Pharmacology & Mechanisms(99)

Affinity: The strength with which a peptide binds to its target receptor, described by the dissociation constant (Kd). High affinity (low Kd) typically correlates with greater potency and longer receptor occupancy.
Allosteric modulation: The modification of receptor activity by a molecule binding to a site distinct from the primary ligand binding site. Allosteric modulators can enhance (positive) or reduce (negative) the receptor’s response to its natural ligand.
AMPK: AMP-activated protein kinase, a master cellular energy sensor that activates catabolic pathways (glucose uptake, fat oxidation) and inhibits anabolic pathways when cellular energy is low. Activated by MOTS-c, exercise, and metformin.
Angiogenesis: The formation of new blood vessels from existing vasculature. A key mechanism by which BPC-157 promotes tissue healing, restoring blood supply to injured areas to accelerate repair.
AOD-9604: A synthetic fragment of human growth hormone (amino acids 177–191) that stimulates lipolysis and inhibits lipogenesis without affecting IGF-1 or insulin.
AUC (area under curve): The total drug exposure over time, calculated as the integral of the concentration-time curve. AUC reflects both the amount absorbed and the rate of elimination. Used to assess bioequivalence.
BDNF: Brain-derived neurotrophic factor, a protein that supports neuron survival, growth, and synaptic plasticity. Critical for learning and memory. Upregulated by peptides like Selank, Semax, and Dihexa.
Binding affinity: The strength of interaction between a peptide and its target receptor, typically expressed as a dissociation constant (Kd). Lower Kd values indicate stronger binding and generally higher potency.
Bioavailability: The fraction of an administered dose that reaches systemic circulation unchanged. Subcutaneous injection provides 65–95% bioavailability for most peptides; oral bioavailability is typically below 1% without absorption enhancers.
Bioequivalence: The demonstration that two peptide products produce equivalent blood levels (Cmax and AUC within 80–125%) when administered at the same dose. Required for generic drug approval.
Blood-brain barrier: A semi-permeable membrane of endothelial cells that separates circulating blood from brain tissue. Most peptides cannot cross the BBB, which is why intranasal delivery is used for neuroactive peptides like Selank and Semax.
BPC: Body Protection Compound. A family of peptides derived from human gastric juice, most commonly referring to BPC-157, a pentadecapeptide studied for gastrointestinal and musculoskeletal healing.
BPC-157: Body Protection Compound-157, a synthetic pentadecapeptide derived from human gastric juice studied for tissue repair, gut healing, and anti-inflammatory effects.
CJC-1295: A synthetic growth hormone-releasing hormone (GHRH) analog that stimulates pulsatile GH secretion. Available with or without DAC (Drug Affinity Complex).
Clearance rate: The volume of blood from which a peptide is completely removed per unit time, expressed in mL/min or L/hr. Clearance determines dosing frequency along with half-life.
Cmax: The maximum (peak) concentration of a peptide in the blood after administration. Cmax is influenced by dose, administration route, and absorption rate.
Competitive inhibition: A mechanism where a molecule competes with the natural ligand for binding to the same receptor site. The effect can be overcome by increasing the concentration of the natural ligand.
Cross-reactivity: The ability of a peptide designed for one receptor to bind to and activate related receptors. For example, Melanotan II activates multiple melanocortin receptor subtypes, producing both tanning and sexual arousal effects.
CYP450: Cytochrome P450, a superfamily of liver enzymes responsible for metabolizing most small-molecule drugs. Peptides are primarily degraded by proteases, not CYP450, which reduces their drug interaction potential.
DAC: Drug Affinity Complex. A modification added to CJC-1295 that enables it to bind to albumin in the bloodstream, extending its half-life from approximately 30 minutes to about 8 days.
Desensitization: A rapid decrease in receptor responsiveness to a peptide agonist despite continued exposure. Distinct from downregulation — desensitization involves receptor modification rather than reduced receptor numbers.
Dihexa: A synthetic hexapeptide analog of angiotensin IV studied for cognitive enhancement. Shown to be 10 million times more potent than BDNF in some assays.
Distribution half-life: The time required for a peptide to distribute from the bloodstream into tissues during the initial distribution phase. Typically much shorter than the elimination half-life.
Dose-response curve: A graph showing the relationship between peptide dose and the magnitude of biological effect. Typically S-shaped (sigmoidal), with a threshold dose, linear range, and plateau at maximum effect.
Downregulation: A decrease in the number or sensitivity of receptors on a cell surface in response to prolonged agonist exposure. Downregulation reduces peptide effectiveness over time and is why cycling is recommended.
DSIP: Delta Sleep-Inducing Peptide, a naturally occurring nonapeptide that modulates sleep architecture and stress responses.
EC50: The concentration of a peptide that produces 50% of its maximum possible effect. A lower EC50 indicates greater potency. Used to compare the relative potency of different peptides acting on the same receptor.
Efficacy: The maximum therapeutic effect a peptide can produce regardless of dose. Distinct from potency — a peptide can be less potent but have greater efficacy, meaning it produces a larger maximum effect.
Elimination half-life: The time required for the blood concentration of a peptide to decrease by 50% during the elimination phase. Determines how long a peptide remains active and how frequently it must be dosed.
Epithalon: A synthetic tetrapeptide (Ala-Glu-Asp-Gly) modeled after Epithalamin that activates telomerase and promotes melatonin production. Studied for anti-aging.
First-pass metabolism: The metabolism of an orally administered peptide by the gut wall and liver before it reaches systemic circulation. First-pass effect dramatically reduces oral bioavailability for most peptides.
Follistatin: A glycoprotein that inhibits myostatin and activin, promoting muscle growth. Studied for its role in muscle hypertrophy and metabolic regulation.
GHK-Cu: A naturally occurring copper-binding tripeptide that stimulates collagen synthesis, modulates over 4,000 genes, and declines with age.
GHRH: Growth hormone-releasing hormone, a 44-amino acid hypothalamic peptide that stimulates pulsatile GH secretion from the anterior pituitary. Sermorelin, CJC-1295, and tesamorelin are synthetic analogs of GHRH.
GHRP: Growth Hormone Releasing Peptide. A class of synthetic peptides (GHRP-2, GHRP-6) that stimulate GH release through the ghrelin receptor. Often stacked with GHRH analogs for synergistic GH secretion.
GIP: Glucose-dependent insulinotropic polypeptide, an incretin hormone that enhances insulin secretion and may regulate fat metabolism. Co-targeted alongside GLP-1 by tirzepatide and retatrutide for enhanced weight loss.
GLP-1: Glucagon-like peptide-1, an incretin hormone that stimulates insulin secretion, suppresses glucagon, slows gastric emptying, and reduces appetite. The therapeutic target of blockbuster drugs semaglutide, tirzepatide, and liraglutide.
Growth factor: A naturally occurring protein that stimulates cell growth, proliferation, and differentiation. Many peptides work by modulating growth factor signaling, including IGF-1, VEGF (vascular endothelial growth factor), and EGF (epidermal growth factor).
Growth hormone secretagogue: A compound that stimulates the pituitary gland to release growth hormone by activating the ghrelin receptor or GHRH receptor. Includes peptides (ipamorelin, GHRP-2, GHRP-6) and the oral compound MK-677.
Half-life: The time required for the concentration of a peptide in the body to decrease by half. Determines dosing frequency — short half-life peptides (minutes) need daily dosing, while long half-life peptides (days) can be dosed weekly.
Hepatic metabolism: The breakdown of peptides by liver enzymes. Most peptides are degraded by proteases rather than CYP450 enzymes, which means fewer drug-drug interactions compared to small-molecule drugs.
Humanin: A mitochondria-derived peptide with cytoprotective and neuroprotective properties. Studied for Alzheimer’s disease and age-related cellular stress.
IC50: The concentration of an inhibitor required to reduce a biological process by 50%. Used to measure the potency of peptide antagonists and enzyme inhibitors.
IGF-1: Insulin-like growth factor 1, a hormone produced primarily by the liver in response to growth hormone. Mediates many of GH’s anabolic effects including muscle growth, bone density, and tissue repair.
Ipamorelin: A selective growth hormone secretagogue that stimulates GH release through the ghrelin receptor with minimal effect on cortisol or prolactin.
KPV: A tripeptide (Lys-Pro-Val) derived from alpha-MSH with potent anti-inflammatory properties, studied for gut health and skin conditions.
Lipogenesis: The metabolic process of synthesizing fatty acids and triglycerides for fat storage. Occurs primarily in the liver and adipose tissue. Inhibited by peptides like AOD-9604 and growth hormone fragments.
Lipolysis: The metabolic process of breaking down stored triglycerides into free fatty acids and glycerol for energy use. Stimulated by growth hormone, GH fragments (AOD-9604), and GLP-1 receptor agonists.
Liraglutide: A GLP-1 receptor agonist FDA-approved for type 2 diabetes (Victoza) and weight management (Saxenda). Administered as a daily injection.
LL-37: A human cathelicidin antimicrobial peptide with broad-spectrum activity against bacteria, viruses, and fungi. Part of innate immune defense.
Maximum tolerated dose: The highest dose of a peptide that can be administered without causing unacceptable side effects. Determined in Phase 1 clinical trials through dose-escalation studies.
Melanocortin receptor: A family of five G protein-coupled receptors (MC1R–MC5R) involved in pigmentation, appetite regulation, sexual function, and inflammation. Targeted by PT-141 (MC3R/MC4R) and Melanotan II (multiple subtypes).
Melanotan II: A synthetic analog of alpha-MSH that activates melanocortin receptors to stimulate melanogenesis (tanning) and sexual arousal.
Metabolite: A breakdown product formed when the body metabolizes a peptide. Some metabolites are active and contribute to therapeutic effects; others are inactive waste products cleared by the kidneys or liver.
Minimum effective dose: The lowest dose of a peptide that produces a statistically significant therapeutic effect. Starting at the MED minimizes side effects while maintaining efficacy.
MK-677: Ibutamoren, an oral growth hormone secretagogue that mimics ghrelin signaling to increase GH and IGF-1 levels over 24 hours.
MOTS-c: A mitochondria-derived peptide that regulates metabolic homeostasis by activating AMPK. Studied for exercise mimetic effects and metabolic health.
Myostatin: A protein (GDF-8) that negatively regulates skeletal muscle growth. Inhibiting myostatin via follistatin or myostatin antibodies allows greater muscle hypertrophy. Myostatin-knockout animals show dramatic muscle growth.
NAD+: Nicotinamide adenine dinucleotide, a coenzyme essential for cellular energy metabolism, DNA repair, and sirtuin activation. Declines with age.
Orforglipron: An investigational oral non-peptide GLP-1 receptor agonist. If approved, would be the first oral GLP-1 that doesn’t require fasting before dosing.
Peak level: The highest concentration of a peptide in the blood after administration, synonymous with Cmax. Peak levels that exceed the therapeutic window may cause dose-dependent side effects.
Pharmacodynamics: The study of what a peptide does to the body — its mechanism of action, therapeutic effects, and side effects at the molecular, cellular, and organ level. Complements pharmacokinetics.
Pharmacokinetics: The study of how the body absorbs, distributes, metabolizes, and excretes a peptide over time (what the body does to the drug). Described by parameters including Cmax, Tmax, AUC, half-life, and clearance.
Phase 1 trial: The first stage of human clinical testing, focused on safety, tolerability, pharmacokinetics, and dose-ranging in 20–100 healthy volunteers. Determines the maximum tolerated dose.
Phase 2 trial: The clinical trial stage that evaluates efficacy, optimal dosing, and side effects in 100–300 patients with the target condition. Phase 2 results determine whether to proceed to large Phase 3 trials.
Phase 3 trial: Large-scale randomized controlled trials (1,000–3,000+ patients) comparing the investigational peptide to placebo or standard of care. Positive Phase 3 results are required for FDA approval.
Plasma protein binding: The binding of a peptide to proteins in the blood (primarily albumin). Only the unbound (free) fraction is pharmacologically active. High protein binding extends half-life but reduces the free active concentration.
Potency: The amount of a peptide required to produce a given effect. A more potent peptide achieves the same effect at a lower dose. Measured by EC50 — lower EC50 means higher potency.
Preclinical: The research stage involving in vitro (cell culture) and in vivo (animal) studies before human clinical trials begin. Most peptides outside GLP-1 agonists remain at this evidence stage.
Prodrug: An inactive or less active form of a peptide that is converted to the active form in the body through enzymatic or chemical processes. Prodrug design can improve oral bioavailability or targeting.
PT-141: Bremelanotide, a melanocortin receptor agonist FDA-approved as Vyleesi for hypoactive sexual desire disorder (HSDD) in premenopausal women.
Receptor agonist: A molecule that binds to and activates a receptor, triggering a biological response. Semaglutide is a GLP-1 receptor agonist; ipamorelin is a ghrelin receptor agonist.
Receptor antagonist: A molecule that binds to a receptor without activating it, blocking the natural ligand from binding. Used in research to study receptor function and as therapeutic agents.
Renal clearance: The removal of a peptide from the blood by the kidneys. Smaller peptides (below ~60 kDa) are filtered by the glomerulus. PEGylation increases molecular size to reduce renal clearance and extend half-life.
Retatrutide: An investigational triple-agonist peptide targeting GIP, GLP-1, and glucagon receptors. Phase 2 trials showed 24.2% weight loss at 48 weeks.
Selank: A synthetic heptapeptide analog of tuftsin with anxiolytic and nootropic properties. Modulates serotonin, dopamine, and BDNF without sedation.
Selectivity: The ability of a peptide to preferentially bind to one receptor subtype over others. Ipamorelin is considered a selective GH secretagogue because it stimulates GH release without significantly affecting cortisol or prolactin.
Semaglutide: A GLP-1 receptor agonist FDA-approved for type 2 diabetes (Ozempic) and weight management (Wegovy). Reduces appetite and slows gastric emptying.
Semax: A synthetic heptapeptide derived from ACTH(4-10) with neuroprotective and cognitive-enhancing properties. Approved in Russia for stroke and cognitive disorders.
Sermorelin: A synthetic GHRH analog (first 29 amino acids of GHRH) used to stimulate natural growth hormone production. Previously FDA-approved for GH deficiency diagnosis.
SS-31: Elamipretide, a mitochondria-targeted tetrapeptide that stabilizes cardiolipin in the inner mitochondrial membrane to restore cellular energy production.
Steady state: The condition where the rate of peptide administration equals the rate of elimination, resulting in consistent plasma levels. Typically reached after 4–5 half-lives of regular dosing.
Survodutide: An investigational dual glucagon/GLP-1 receptor agonist in development for obesity and metabolic liver disease (MASH).
Systemic bioavailability: The fraction of an administered dose that reaches the general circulation and is available to exert its effects throughout the body. Intravenous injection has 100% systemic bioavailability by definition.
Tachyphylaxis: A rapid decrease in the response to a peptide after repeated administration within a short timeframe. More acute and pronounced than tolerance. Pulsatile dosing and cycling help prevent tachyphylaxis.
TB: Thymosin Beta. Refers to the thymosin beta peptide family, including TB-500 (a synthetic fragment of Thymosin Beta-4) studied for wound healing and tissue repair.
TB-500: A synthetic version of Thymosin Beta-4, a 43-amino acid peptide that promotes healing through actin upregulation, angiogenesis, and inflammation reduction.
Telomerase: An enzyme that maintains telomere length by adding TTAGGG repeats to chromosome ends. Telomerase activity declines with age. Epithalon has been shown to activate telomerase in human somatic cells.
Telomere: Repetitive DNA sequences (TTAGGG in humans) at the ends of chromosomes that protect genetic material during cell division. Telomeres shorten with each division; critically short telomeres trigger cellular senescence.
Tesamorelin: A synthetic GHRH analog FDA-approved (Egrifta) for HIV-associated lipodystrophy. Stimulates pulsatile growth hormone release.
Therapeutic window: The range of peptide concentrations between the minimum effective dose and the dose producing unacceptable side effects. A narrow therapeutic window requires careful dose titration and monitoring.
Thymosin Alpha-1: A 28-amino acid peptide that modulates immune function by enhancing T-cell maturation and dendritic cell activity. Approved in several countries for hepatitis B.
Thymosin Beta-4: A 43-amino acid peptide involved in actin sequestration, wound healing, and tissue repair. The natural form of which TB-500 is a synthetic fragment.
Tirzepatide: A dual GIP/GLP-1 receptor agonist FDA-approved for type 2 diabetes (Mounjaro) and weight loss (Zepbound). Achieves 20–25% body weight reduction in clinical trials.
Tmax: The time after administration at which maximum peptide concentration (Cmax) is reached. Subcutaneous peptides typically reach Tmax in 1–4 hours.
Tolerance: A gradual decrease in the effectiveness of a peptide with chronic use, requiring higher doses to achieve the same effect. Managed through cycling, dose adjustments, or peptide switching.
Trough level: The lowest concentration of a peptide in the blood, measured just before the next dose. Trough levels should remain above the minimum effective concentration for optimal therapeutic effect.
Upregulation: An increase in the number or sensitivity of receptors on a cell surface, often in response to decreased stimulation. Can occur during wash-out periods and is the mechanism behind cycling protocols.
Volume of distribution: A pharmacokinetic parameter relating the total amount of drug in the body to the plasma concentration. A large Vd indicates extensive tissue distribution; a small Vd suggests the peptide stays primarily in the bloodstream.

Administration & Dosing(43)

Alcohol swab: A pre-saturated pad containing 70% isopropyl alcohol used to disinfect injection sites and vial stoppers before needle insertion. Essential for maintaining aseptic technique.
Ampoule: A small sealed glass container holding a single dose of liquid peptide or diluent. Unlike vials, ampoules are snapped open and the entire contents must be used immediately.
Aseptic technique: A set of practices to prevent contamination during peptide preparation and injection. Includes swabbing vial stoppers with alcohol, using new needles for each draw, and working in a clean environment.
Auto-injector: A pre-filled, spring-loaded device that automatically delivers a set dose of peptide with the push of a button. Used for FDA-approved peptides like Ozempic (semaglutide) and Mounjaro (tirzepatide).
Bacteriostatic saline: A 0.9% sodium chloride solution containing benzyl alcohol as a preservative. Used as an alternative to bacteriostatic water for peptide reconstitution when isotonicity is desired to reduce injection-site irritation.
Bacteriostatic water: Sterile water containing 0.9% benzyl alcohol as a preservative. Preferred for reconstituting peptides because the preservative inhibits bacterial growth, allowing multiple draws from the same vial over 28 days.
Bolus injection: A single, relatively rapid injection of a peptide as opposed to a slow infusion. Most subcutaneous peptide administrations are bolus injections.
Continuous infusion: Slow, sustained delivery of a peptide over an extended period using an infusion pump or IV drip. Used in clinical settings for NAD+ infusions and some research peptides.
Cycling: The practice of using a peptide for a set period (on-cycle) followed by a break (off-cycle) to maintain receptor sensitivity, reduce side effects, and prevent tolerance. Typical cycles range from 4–12 weeks on, 2–4 weeks off.
Dose titration: The practice of gradually increasing a peptide dose over time to assess individual tolerance and find the minimum effective dose while minimizing side effects. Standard practice with GLP-1 agonists.
Gauge (needle): A measurement of needle diameter — higher gauge numbers indicate thinner needles. Subcutaneous peptide injections typically use 27–31 gauge needles. Thinner needles reduce pain but draw liquid more slowly.
IM: Intramuscular. Medical abbreviation for injection directly into muscle tissue. Less common than subcutaneous for peptides but used when faster absorption is desired.
Injection site rotation: The practice of alternating injection locations (abdomen, thigh, upper arm, glute) to prevent lipodystrophy, scar tissue buildup, and localized irritation. Sites should be at least 1 inch apart.
Intramuscular injection: An injection delivered directly into muscle tissue, providing faster absorption than subcutaneous injection. Used for some peptides when deeper tissue penetration or more rapid onset is desired.
Intranasal administration: Delivery of a peptide through the nasal mucosa, bypassing the blood-brain barrier for some compounds. Used for peptides like Selank and Semax that target the central nervous system.
Intravenous injection: An injection directly into a vein, providing immediate systemic bioavailability. Rarely used for self-administered peptides but common in clinical settings for research peptides and NAD+ infusions.
IU: International Units. A standardized measurement used for some biologics and peptides, particularly growth hormone (1 IU = approximately 0.33 mg) and insulin. Conversion factors vary by substance.
Loading dose: An initial higher dose used at the start of a protocol to quickly reach therapeutic levels in the body before transitioning to a lower maintenance dose. Common with CJC-1295 with DAC and some GLP-1 agonists.
Lyophilized powder: A freeze-dried peptide in powder form. Lyophilization removes water to create a shelf-stable product that must be reconstituted with bacteriostatic water before injection.
Maintenance dose: The ongoing dose administered after an initial loading phase to sustain therapeutic peptide levels in the body. Typically lower than the loading dose.
mcg: Microgram. One millionth of a gram (0.001 mg or 1,000 nanograms). The standard unit for peptide dosing. Also abbreviated as µg. Most research peptides are dosed in the 100–1,000 mcg range.
Micro-dosing: The practice of administering very small doses of a peptide, often 1/10th to 1/5th of a standard dose. Used to minimize side effects while potentially maintaining therapeutic benefits.
Oral administration: Delivery of a peptide by mouth in tablet or capsule form. Most peptides have poor oral bioavailability due to enzymatic degradation in the GI tract, though new formulations like oral semaglutide (Rybelsus) use absorption enhancers.
PCT (post cycle therapy): A protocol of supplements or medications used after discontinuing a peptide cycle to restore the body’s natural hormone production and maintain gains. More commonly associated with anabolic compounds.
Pen injector: A reusable or disposable injection device shaped like a pen that holds a multi-dose cartridge of peptide. Allows precise dial-a-dose selection and uses small-gauge disposable pen needles.
Pulsatile dosing: A dosing strategy that mimics the body’s natural pulsatile hormone release patterns. Used with growth hormone secretagogues to prevent receptor desensitization and maintain physiological GH release.
Reconstitution: The process of dissolving a lyophilized (freeze-dried) peptide powder with bacteriostatic water or sterile water before injection. Proper reconstitution technique is critical — the diluent should be added slowly along the vial wall to avoid damaging the peptide.
Saturation dose: The dose at which all available receptors are occupied and further increases produce no additional effect. Exceeding saturation dose wastes peptide and may increase side effects.
SC: Subcutaneous. Medical abbreviation for the injection route into fatty tissue beneath the skin, the most common method for self-administered peptide injections.
Sharps container: A puncture-resistant, leak-proof container for safe disposal of used needles and syringes. Required by most local regulations for proper medical waste management.
Sodium chloride: Salt (NaCl) used in 0.9% solution (normal saline) as a diluent for some peptides. Physiologically isotonic, meaning it matches the body’s natural fluid concentration.
Split dosing: Dividing a total daily peptide dose into two or more smaller administrations throughout the day. Used with short-half-life peptides to maintain more stable blood levels.
Stacking: Using two or more peptides simultaneously to achieve complementary or synergistic effects. Common stacks include CJC-1295 + Ipamorelin for GH release and BPC-157 + TB-500 for tissue healing.
Sterile water: Water that has been sterilized and is free of microorganisms but contains no preservative. Unlike bacteriostatic water, vials should be used within 24 hours of opening due to contamination risk.
Subcutaneous injection: An injection into the fatty tissue layer between the skin and muscle. The most common administration route for peptides, typically using insulin syringes. Preferred for its slow, steady absorption and ease of self-administration.
Sublingual administration: Placement of a peptide under the tongue for absorption through the oral mucosa. Bypasses first-pass metabolism and provides faster onset than oral administration, though bioavailability varies by peptide.
Syringe units: Measurement markings on insulin syringes, where 100 units = 1 mL. Understanding syringe units is essential for accurate peptide dosing after reconstitution.
Taper protocol: A gradual reduction in peptide dose over time before discontinuation to prevent rebound effects, withdrawal symptoms, or hormonal disruption. The opposite approach to a loading dose.
Titration schedule: A predefined plan for gradually increasing peptide dosage over weeks. For example, semaglutide starts at 0.25mg weekly for 4 weeks, then increases to 0.5mg, 1mg, and so on.
Topical application: Application of a peptide directly to the skin surface for local effects. Common for copper peptides (GHK-Cu) in skincare and BPC-157 formulations targeting localized injury sites.
Transdermal delivery: Delivery of a peptide through the skin, typically via patches, creams, or gels. Provides sustained release but is limited by molecular weight — most peptides are too large for passive transdermal absorption.
Vial: A small glass or plastic container sealed with a rubber stopper and aluminum crimp cap, used to store lyophilized or reconstituted peptides. Typically 2mL–10mL capacity.
Washout period: The time between stopping one peptide protocol and starting another, allowing the compound to be fully eliminated from the body. Typically 5–7 half-lives long.

Chemistry & Structure(37)

Actin: A globular protein that forms microfilaments in the cytoskeleton. Thymosin Beta-4 sequesters actin monomers and regulates actin polymerization, which is essential for cell migration and wound healing.
Aggregation: The clumping together of peptide molecules, which can reduce biological activity and potentially cause injection-site reactions. Prevented by proper reconstitution technique (gentle swirling, not shaking) and correct storage temperature.
Amino acid: An organic molecule containing both an amino group (-NH2) and a carboxyl group (-COOH). The 20 standard amino acids are the building blocks of peptides and proteins, linked together by peptide bonds.
Amino acid sequence: The specific linear order of amino acids in a peptide chain, written from N-terminus to C-terminus. The sequence determines the peptide’s three-dimensional structure and biological activity.
Analog: A synthetic peptide with a modified amino acid sequence compared to the natural version, designed to improve potency, stability, or half-life. Semaglutide is an analog of natural GLP-1 with 94% sequence homology.
Buffer solution: A solution that resists changes in pH when small amounts of acid or base are added. Peptide formulations use buffers (acetate, phosphate, histidine) to maintain the optimal pH for stability.
C-terminus: The end of a peptide chain with a free carboxyl group (-COOH). C-terminal modifications such as amidation can enhance peptide stability and receptor binding.
Chirality: The property of a molecule that is non-superimposable on its mirror image. Natural amino acids are L-form (left-handed); D-form amino acids can be incorporated into peptides to resist enzymatic degradation.
Cyclization: The process of forming a ring structure within a peptide chain, typically through disulfide bonds or amide bonds between the N- and C-termini. Cyclization increases stability, receptor selectivity, and resistance to enzymatic degradation.
Deamidation: A chemical degradation pathway where asparagine or glutamine residues lose their amide group. Deamidation alters peptide charge and structure, reducing biological activity. Accelerated by heat and alkaline pH.
Degradation: The breakdown of a peptide through chemical processes like oxidation, deamidation, or hydrolysis. Degredation reduces potency and may produce inactive or harmful byproducts. Proper storage conditions minimize degradation.
Disulfide bond: A covalent bond formed between two cysteine residues in a peptide chain. Disulfide bonds stabilize three-dimensional structure and are critical for the biological activity of many peptides including insulin.
Enantiomer: One of two mirror-image forms of a chiral molecule. L-amino acids and D-amino acids are enantiomers. D-amino acid substitutions in peptides increase protease resistance and oral bioavailability.
Endotoxin: A toxic component of gram-negative bacterial cell walls (lipopolysaccharide). Endotoxin contamination in peptide preparations can cause fever, inflammation, and sepsis. Pharmaceutical-grade peptides are tested to be below endotoxin limits.
Excipient: An inactive ingredient added to a peptide formulation to improve stability, solubility, or delivery. Common excipients include mannitol (bulking agent), sucrose (cryoprotectant), and phosphate buffers.
Freeze-drying: A dehydration process synonymous with lyophilization. The peptide solution is frozen, then pressure is reduced to allow ice to sublimate directly to vapor, producing a stable dry powder.
GHK: Glycyl-histidyl-lysine, a naturally occurring tripeptide. GHK-Cu is its copper-bound form with enhanced biological activity including collagen synthesis stimulation and gene modulation.
HPLC (high performance liquid chromatography): An analytical technique that separates, identifies, and quantifies components in a mixture. Used to determine peptide purity — results are reported as a percentage (e.g., 98% purity by HPLC).
Isoform: A naturally occurring variant of a peptide or protein that differs slightly in amino acid sequence but retains similar function. Different isoforms may have different tissue distributions or activity levels.
Lyophilization: The freeze-drying process that removes water from a peptide solution by sublimation under vacuum. Creates a stable, shelf-stable powder with a characteristic "puck" or "cake" appearance in the vial.
Mass spectrometry: An analytical technique that measures the mass-to-charge ratio of molecules. Used to confirm peptide identity by verifying molecular weight matches the expected sequence. Essential for quality control.
Molecular weight: The sum of atomic weights of all atoms in a peptide molecule, measured in Daltons (Da). Peptides are generally 500–5,000 Da; larger molecules are classified as proteins. Molecular weight affects bioavailability and delivery route.
N-terminus: The end of a peptide chain with a free amino group (-NH2). By convention, peptide sequences are written starting from the N-terminus. Modifications at the N-terminus can affect stability and half-life.
Osmolality: The concentration of dissolved particles in a solution, measured in mOsm/kg. Peptide solutions should be close to physiological osmolality (275–295 mOsm/kg) to minimize injection-site pain and tissue damage.
Oxidation: A chemical reaction that can damage methionine and cysteine residues in peptides, reducing activity. Oxidation is accelerated by light, heat, and oxygen exposure. Prevented by proper storage in amber vials with desiccant.
PEGylation: The covalent attachment of polyethylene glycol (PEG) chains to a peptide. PEGylation increases molecular size, reduces renal clearance, and extends half-life. Used in semaglutide and other long-acting peptide drugs.
Peptide bond: A covalent chemical bond formed between the carboxyl group of one amino acid and the amino group of another through a condensation reaction. Peptide bonds link amino acids into peptide chains.
Peptide synthesis: The chemical process of creating peptides by linking amino acids together. Can be performed in solution or on solid phase. Commercial peptides are almost exclusively made via solid-phase peptide synthesis (SPPS).
pH: A measure of acidity or alkalinity on a scale of 0–14, where 7 is neutral. Most peptides are most stable at slightly acidic pH (4–6). Incorrect pH accelerates degradation through deamidation and aggregation.
Primary structure: The linear sequence of amino acids in a peptide, representing the most fundamental level of structural organization. All higher-order structure and function derive from the primary sequence.
Purity percentage: The proportion of the desired peptide in a sample, determined by HPLC analysis. Research-grade peptides are typically 95–98% pure; pharmaceutical-grade exceeds 99%. Higher purity reduces the risk of adverse reactions.
Pyrogen: Any substance that causes fever when introduced into the body. Endotoxins are the most common pyrogens in pharmaceutical products. Peptides must be tested and confirmed to be pyrogen-free.
Racemization: The conversion of an L-amino acid to its D-enantiomer during synthesis or storage. Racemization reduces peptide activity and is a sign of degradation. Proper storage and synthesis conditions minimize this.
Secondary structure: Local folding patterns in a peptide chain, primarily alpha-helices and beta-sheets, stabilized by hydrogen bonds between backbone atoms. Determines how the peptide interacts with receptors.
Solid phase synthesis: A method of peptide synthesis where the growing peptide chain is attached to an insoluble resin bead. Amino acids are added one at a time, enabling automation and high throughput. Developed by Robert Bruce Merrifield (Nobel Prize, 1984).
Stability: A peptide’s resistance to chemical degradation over time. Affected by temperature, pH, light, and oxidation. Lyophilized peptides are most stable; reconstituted peptides should be refrigerated and used within 28 days.
Tertiary structure: The overall three-dimensional shape of a folded peptide or protein, determined by interactions between side chains including disulfide bonds, hydrophobic interactions, and ionic bonds.

Conditions & Health(30)

Autoimmune disease: A condition where the immune system mistakenly attacks the body’s own tissues. Immunomodulatory peptides like Thymosin Alpha-1 and KPV are studied for their ability to balance immune responses.
Cachexia: A severe wasting syndrome characterized by loss of muscle and fat tissue, often associated with cancer, HIV, or chronic disease. Distinct from sarcopenia in its metabolic and inflammatory drivers.
Chronic fatigue syndrome: A complex disorder characterized by extreme fatigue not explained by underlying medical conditions, worsened by physical or mental exertion. Mitochondrial peptides (SS-31, MOTS-c) and NAD+ are being explored.
Edema: Swelling caused by excess fluid trapped in body tissues. Can be a side effect of some peptides (particularly GH secretagogues) due to fluid retention, usually dose-dependent and resolving with dose adjustment.
Fibromyalgia: A chronic pain condition characterized by widespread musculoskeletal pain, fatigue, and cognitive difficulties. Some patients explore BPC-157 and anti-inflammatory peptides as complementary approaches.
Fibrosis: The excessive formation of fibrous connective tissue in an organ, impairing its function. Can affect the liver (cirrhosis), lungs (pulmonary fibrosis), or any injured tissue. Anti-fibrotic peptide research is active.
Growth hormone deficiency: Inadequate production of growth hormone by the pituitary gland, causing reduced muscle mass, increased body fat, decreased bone density, and impaired quality of life. GH secretagogues and GHRH analogs are studied as alternatives to direct GH injection.
HSDD: Hypoactive Sexual Desire Disorder. A condition characterized by persistently low sexual desire causing personal distress. PT-141 (bremelanotide, brand name Vyleesi) is the first FDA-approved peptide treatment for HSDD.
Hypogonadism: A condition where the body produces insufficient sex hormones (testosterone or estrogen). Growth hormone secretagogues may indirectly support hormonal balance by optimizing GH/IGF-1 axis function.
Hypothyroidism: Underactive thyroid gland producing insufficient thyroid hormones, leading to fatigue, weight gain, and cold intolerance. Some peptide protocols address secondary effects through metabolic optimization.
Immunodeficiency: A state where the immune system’s ability to fight infections is compromised, either inherited or acquired. Thymosin Alpha-1 is approved in some countries to boost immune function in immunocompromised patients.
Inflammation: The body’s immune response to injury, infection, or irritation. Acute inflammation is protective; chronic inflammation drives disease. Many peptides (BPC-157, KPV, LL-37, Thymosin Alpha-1) modulate inflammatory pathways.
Inflammatory bowel disease: Chronic inflammatory conditions of the gastrointestinal tract, including Crohn’s disease and ulcerative colitis. BPC-157 and KPV show anti-inflammatory effects in preclinical IBD models.
Insulin resistance: A condition where cells respond poorly to insulin, requiring the pancreas to produce more insulin to maintain normal blood sugar. A precursor to type 2 diabetes. GLP-1 agonists improve insulin sensitivity.
Leaky gut: Increased intestinal permeability allowing bacteria, toxins, and undigested food particles to pass through the gut lining. BPC-157 has been shown to restore gut barrier integrity in animal models.
Lipodystrophy: Abnormal distribution or loss of fat tissue, which can be genetic or acquired (e.g., from HIV treatment or repeated injections at the same site). Tesamorelin is FDA-approved for HIV-associated lipodystrophy.
MASH: Metabolic dysfunction-associated steatohepatitis (formerly NASH). Inflammatory liver disease with fat accumulation, hepatocyte damage, and fibrosis risk. Survodutide and semaglutide are in trials for MASH treatment.
Metabolic syndrome: A cluster of conditions including central obesity, elevated blood sugar, high blood pressure, and abnormal cholesterol that together increase the risk of heart disease, stroke, and type 2 diabetes.
Mitochondrial dysfunction: Impaired mitochondrial function leading to reduced cellular energy (ATP) production. Contributes to aging, neurodegeneration, and metabolic disease. Targeted by mitochondria-derived peptides SS-31, MOTS-c, and Humanin.
NAFLD (non-alcoholic fatty liver disease): Accumulation of fat in the liver not caused by alcohol consumption, affecting up to 30% of adults. Can progress to MASH (inflammatory liver damage). GLP-1 agonists and survodutide show promise in reducing liver fat.
Neuropathy: Damage or dysfunction of one or more peripheral nerves, causing pain, numbness, or weakness. BPC-157 and NGF-related peptides are studied for nerve regeneration in preclinical models.
Obesity: A chronic disease defined by BMI ≥ 30, characterized by excess adipose tissue. GLP-1 agonists have revolutionized obesity treatment, with semaglutide (Wegovy) and tirzepatide (Zepbound) achieving 15–25% weight loss.
Osteoarthritis: Degenerative joint disease involving cartilage breakdown, bone changes, and inflammation. Peptides like BPC-157 are studied for cartilage repair and joint healing in preclinical models.
Oxidative stress: An imbalance between free radical production and antioxidant defenses, causing cellular damage. Mitochondrial peptides (SS-31, MOTS-c, Humanin) and GHK-Cu reduce oxidative stress through different mechanisms.
Sarcopenia: Age-related loss of skeletal muscle mass and strength that typically begins after age 30, accelerating after 60. Peptides targeting GH secretion (ipamorelin, CJC-1295) and myostatin inhibition (follistatin) are studied as interventions.
Scar tissue: Dense, fibrous connective tissue that replaces normal tissue after injury. Peptides like BPC-157 and TB-500 may improve scar remodeling by promoting organized collagen deposition and reducing fibrosis.
Tendinopathy: Chronic tendon pain and dysfunction caused by degeneration rather than acute inflammation. BPC-157 and TB-500 are studied for tendon healing through angiogenesis and collagen remodeling.
Traumatic brain injury: Damage to the brain caused by external mechanical force. Neuroprotective peptides like Semax, BPC-157, and DSIP are studied for TBI recovery through neuroplasticity enhancement and inflammation reduction.
Type 2 diabetes: A metabolic disease characterized by chronically elevated blood sugar due to insulin resistance and inadequate insulin secretion. GLP-1 agonists (semaglutide, tirzepatide, liraglutide) are first-line treatments.
Wound healing: The biological process of tissue repair following injury, involving inflammation, proliferation, and remodeling phases. BPC-157, TB-500, and GHK-Cu accelerate various stages of wound healing in preclinical studies.

Equipment & Quality(20)

Amber vial: A dark brown glass vial that filters UV and visible light to protect light-sensitive peptides from photodegradation. Standard for pharmaceutical peptide storage.
Certificate of analysis: A document from a laboratory confirming the identity, purity, and quality of a peptide batch. Should include HPLC purity percentage, mass spectrometry confirmation, and endotoxin levels. Essential for verifying peptide quality.
Cleanroom: A controlled environment with filtered air and strict contamination protocols used for pharmaceutical manufacturing. Classified by ISO standards (ISO 5–8) based on allowable particle counts.
Cold chain: An unbroken temperature-controlled supply chain for keeping peptides within a specified temperature range from manufacturing to administration. Critical for maintaining peptide stability during shipping and storage.
Compounding pharmacy: A pharmacy that custom-prepares medications, including peptides, based on a prescriber’s specific order. Compounded peptides are made to order rather than mass-manufactured. Regulated under 503A or 503B frameworks.
Dead space: The small volume of liquid that remains in the syringe hub and needle after the plunger is fully depressed. Can waste 0.02–0.07 mL of peptide per injection. Low dead-space syringes minimize this loss.
Desiccant: A hygroscopic substance (usually silica gel) placed in peptide packaging to absorb moisture and prevent degradation. Essential for maintaining the stability of lyophilized peptide powders during storage.
Endotoxin testing: Laboratory analysis (typically Limulus Amebocyte Lysate or LAL test) to detect and quantify bacterial endotoxins in peptide products. FDA limits are typically <5 EU/kg body weight for injectable products.
GMP (good manufacturing practice): A system of quality assurance standards ensuring products are consistently produced and controlled according to defined quality standards. GMP-grade peptides meet pharmaceutical manufacturing requirements.
Insulin syringe: A small-volume syringe (typically 0.3mL, 0.5mL, or 1mL) with a fixed fine-gauge needle, originally designed for insulin but widely used for subcutaneous peptide injections. Marked in units (100 units = 1 mL).
Laminar flow hood: A work station that provides a sterile environment by directing filtered (HEPA) air in a laminar flow pattern over the work surface. Used in compounding pharmacies and labs for peptide preparation.
Luer lock: A twist-lock connection system between a syringe barrel and needle that prevents accidental detachment. Provides a more secure connection than slip-tip syringes, especially important when drawing from vials.
Peptide storage: The conditions required to maintain peptide stability and potency. Lyophilized peptides should be stored at -20°C for long-term or 2–8°C for short-term. Reconstituted peptides must be refrigerated and used within 28 days.
Pharmaceutical grade: The highest quality standard for a peptide, meeting regulatory requirements for human use. Purity exceeds 99%, with documented manufacturing processes, quality controls, and endotoxin testing.
Research grade: Peptides manufactured for research purposes, not for human use. Typically 95–98% pure. While commonly used in the peptide community, research-grade products have not undergone clinical safety testing.
Sterile filter: A 0.22-micron membrane filter that removes bacteria and particles from solutions. Used in pharmaceutical manufacturing and by compounding pharmacies to sterilize peptide solutions.
Third-party testing: Independent laboratory analysis of a peptide by a facility not affiliated with the manufacturer. Provides unbiased verification of purity, identity, and absence of contaminants. A hallmark of reputable peptide suppliers.
Tuberculin syringe: A 1 mL syringe with fine graduations (0.01 mL increments), used for precise measurement of small volumes. Unlike insulin syringes, tuberculin syringes often have a removable Luer lock needle.
USP grade: A quality standard meeting United States Pharmacopeia specifications for purity, quality, and potency. USP-grade reagents (like bacteriostatic water) meet pharmaceutical standards for human use.
UV protection: Shielding peptides from ultraviolet light, which accelerates oxidation and degradation. Achieved through amber vials, opaque packaging, and dark storage conditions.

Regulations & Compliance(20)

503A pharmacy: A traditional compounding pharmacy that prepares medications based on individual prescriptions. 503A pharmacies are state-regulated, require a patient-specific prescription, and do not need FDA registration.
503B outsourcing facility: A compounding facility registered with the FDA that can produce large batches without patient-specific prescriptions. Subject to FDA inspection, current good manufacturing practices (cGMP), and adverse event reporting.
Adverse event reporting: The systematic reporting of negative health effects associated with drug use. Healthcare providers and manufacturers are required to report serious adverse events to the FDA via the MedWatch system.
BLA (biologics license application): The regulatory pathway for approval of biological products (including some peptides and proteins) by the FDA. Similar to an NDA but specifically for biologics derived from living organisms.
Clinical trial phases: The staged process of testing a new drug in humans: Phase 1 (safety), Phase 2 (efficacy), Phase 3 (large-scale confirmation), and Phase 4 (post-marketing surveillance). Each phase has specific objectives and requirements.
Compounded medication: A custom-prepared drug made by a compounding pharmacy to meet an individual patient’s needs. Compounded peptides (like compounded semaglutide) exist in a regulatory gray area that the FDA has increasingly scrutinized.
Controlled substance: A drug regulated by the government due to abuse potential. Human growth hormone is a controlled substance (Schedule III); most peptides are not scheduled but may be regulated as research chemicals or unapproved drugs.
DSHEA: The Dietary Supplement Health and Education Act of 1994. Defines the regulatory framework for dietary supplements in the U.S. Peptides generally do not qualify as dietary supplements under DSHEA.
FDA approved: A designation indicating the U.S. Food and Drug Administration has determined a drug is safe and effective for its labeled indication based on clinical trial evidence. FDA-approved peptides include semaglutide, tirzepatide, liraglutide, and PT-141.
GLP compliance: Good Laboratory Practice, a quality system for non-clinical laboratory studies. GLP-compliant studies follow standardized procedures for planning, performing, monitoring, and reporting, ensuring data integrity for regulatory submissions.
ICH guidelines: International Council for Harmonisation guidelines that unify pharmaceutical regulatory requirements across the US, EU, and Japan. Cover drug quality, safety, efficacy, and multidisciplinary topics.
IND (investigational new drug): An application submitted to the FDA before human clinical trials can begin. The IND includes preclinical data, manufacturing information, and the proposed clinical trial protocol.
Informed consent: The process by which a patient voluntarily agrees to medical treatment or participation in a clinical trial after being fully informed of the risks, benefits, and alternatives.
IRB (institutional review board): An independent ethics committee that reviews and approves research involving human subjects. IRB approval is required before any clinical trial can begin, ensuring participant safety and ethical conduct.
NDA (new drug application): The formal application to the FDA requesting approval to market a new drug. Contains all clinical trial data, manufacturing details, and proposed labeling. Review takes 6–12 months.
Off-label use: The use of an FDA-approved drug for a purpose, population, or dose not specified in its approved labeling. Physicians may legally prescribe off-label. Many peptide uses in clinics are off-label.
Pharmacovigilance: The science and activities relating to detection, assessment, understanding, and prevention of adverse drug effects. Required for all FDA-approved drugs, including post-marketing surveillance (Phase 4).
Research chemical: A substance sold for in vitro research and not intended for human consumption. Many peptides are sold under this designation, which limits regulatory oversight but also means no clinical safety data for human use.
Schedule III: A DEA classification for drugs with moderate potential for abuse and accepted medical use. Growth hormone is Schedule III, making unauthorized distribution a federal offense.
WADA prohibited list: The World Anti-Doping Agency’s list of substances and methods banned in competitive sports. Many peptides including GH secretagogues, GLP-1 agonists, and EPO-mimetics are on the prohibited list.

This glossary is regularly updated as new peptide research is published.