The Complete Peptide Glossary — Every Term You Need, Explained in Plain English

The Complete Peptide Glossary

Peptide research comes with its own language. Some of it is straightforward once explained. Some of it is borrowed from biochemistry and pharmacology in ways that can make a simple concept sound unnecessarily complex. All of it matters because understanding the terminology is what allows you to read research, evaluate sources and make informed decisions rather than relying on someone else’s interpretation.

This glossary is organised into four categories to make navigation easier. Whether you’ve landed here looking up a specific term or working through the vocabulary systematically, everything you need is here.

Use the categories to navigate:

• [General Peptide Terms]
• [Administration and Practical Terms]
• [Research and Science Terms]
• [Individual Peptide Quick Reference]

General Peptide Terms

Amino Acids The individual building blocks from which peptides and proteins are constructed. There are 20 standard amino acids that the body uses, each with a distinct chemical structure and biological role. When amino acids join together through peptide bonds they form peptide chains. Think of them as the individual letters from which biological sentences are written.

Peptide A short chain of amino acids — typically between 2 and 50 linked together by peptide bonds. Peptides occur naturally throughout the body and serve as biological messengers, signalling cells and organs to carry out specific functions. Research peptides are synthesised versions that mimic, amplify or modulate these natural signalling processes.

Peptide Bond The chemical bond that links individual amino acids together within a peptide chain. Formed when the carboxyl group of one amino acid reacts with the amine group of the next, releasing a water molecule in the process. The peptide bond is what gives the chain its structure and stability.

Protein A longer, more complex chain of amino acids generally defined as containing more than 50 amino acids. Proteins fold into intricate three-dimensional structures that determine their function. While peptides and proteins are made of the same building blocks, their size difference gives them fundamentally different biological roles and behaviour.

Endogenous Peptide A peptide that the body produces naturally. Insulin, oxytocin and glutathione are all endogenous peptides. Understanding that many research peptides are based on or derived from endogenous compounds is important; it explains why the body has existing receptor systems that recognise and respond to them.

Synthetic Peptide A peptide produced in a laboratory setting rather than derived from a biological source. Research peptides are synthetic compounds created to replicate or modify the structure of naturally occurring compounds. The quality of synthesis, including purity and accuracy of the amino acid sequence, varies significantly between sources.

Receptor A protein structure on the surface or interior of a cell that receives and responds to specific biological signals. Peptides work by binding to receptors like a key fitting a lock, triggering a precise cellular response. The specificity of this mechanism is what makes peptides so targeted in their effects.

Secretagogue A compound that stimulates the body to secrete a particular substance. Growth hormone secretagogues such as Ipamorelin and GHRP-6 stimulate the pituitary gland to release growth hormone rather than introducing growth hormone directly. This distinction is significant both mechanistically and in terms of how the body responds.

Agonist A compound that binds to a receptor and activates it, producing a biological response. Many peptides are agonists — they bind to specific receptors and trigger the response associated with that receptor.

Antagonist A compound that binds to a receptor but blocks rather than activates it, preventing the natural signal from landing. Some research compounds are antagonists used to inhibit specific biological processes.

Half-Life The time it takes for the concentration of a compound in the body to reduce by half. Half-life determines how frequently a peptide needs to be administered to maintain effective levels. A peptide with a short half-life, such as Ipamorelin at 2 hours, requires more frequent dosing than one with an extended half-life, such as CJC-1295 with DAC at 6 to 8 days.

Bioavailability The proportion of an administered compound that reaches circulation and is able to have an active effect. Subcutaneous injection typically provides high bioavailability for peptides. Oral administration of most peptides results in very low bioavailability because digestive enzymes break down the amino acid chain before it can be absorbed, which is why most research peptides are administered by injection or intranasally.

Peptide Stack The combination of two or more peptides within the same protocol, chosen for their complementary or synergistic mechanisms. Common examples include CJC-1295 with Ipamorelin for growth hormone support, and BPC-157 with TB-500 for comprehensive tissue repair. Stacking should be approached with an understanding of how each compound interacts.

Cycle A defined period of peptide use followed by a period of rest. Cycling is important for most peptide protocols to prevent receptor desensitisation the process by which receptors become less responsive to a signal when it is present continuously. Cycle lengths vary significantly by peptide and goal.

Desensitisation The process by which receptors become less responsive to repeated stimulation. Relevant to growth hormone releasing peptides in particular, continuous administration without breaks can result in diminishing returns over time. Cycling protocols are designed specifically to prevent this.

HPA Axis The hypothalamic-pituitary-adrenal axis the body’s central stress response system. The HPA axis governs cortisol production and release, and its function is directly relevant to anyone using peptides, since chronic HPA overactivation suppresses growth hormone and disrupts the hormonal environment that peptides work within.

IGF-1 Insulin-like Growth Factor 1 a hormone produced primarily in the liver in response to growth hormone stimulation. IGF-1 is responsible for many of the downstream effects associated with growth hormone, including tissue growth, cellular repair and metabolic regulation. Many growth hormone releasing peptides are evaluated by their effect on IGF-1 levels.

Administration and Practical Terms

Reconstitution The process of mixing lyophilised peptide powder with bacteriostatic water to create a solution suitable for administration. Reconstitution requires care the correct volume of water must be added, and the mixing process should be gentle to avoid degrading the peptide. Each peptide page in the library includes specific reconstitution guidance.

Bacteriostatic Water: Sterile water containing 0.9% benzyl alcohol as a preservative. Used for reconstituting peptides because the benzyl alcohol prevents bacterial growth, allowing the reconstituted solution to be stored and used across multiple doses. Standard sterile water without the preservative is not recommended for multi-dose vials.

Lyophilised The term for freeze-dried the process used to preserve peptides in powder or cake form within a sealed vial. Lyophilisation removes moisture while preserving the peptide’s structural integrity, allowing for longer shelf life at appropriate temperatures. Lyophilised peptides require reconstitution before use.

Subcutaneous (SubQ) Injection into the layer of fatty tissue just beneath the skin the most common administration route for research peptides. Subcutaneous injection is relatively straightforward and provides reliable absorption. Common sites include the abdomen, thigh and upper arm. Rotating injection sites is important to prevent localised tissue irritation.

Intramuscular (IM) Injection directly into muscle tissue. Less commonly used for peptides than subcutaneous administration, but relevant for certain compounds and protocols.

Intranasal Administration via the nasal passage, used for certain peptides including Semax and Selank. Intranasal delivery allows the compound to cross the blood-brain barrier more readily than subcutaneous injection, making it particularly relevant for peptides targeting neurological and cognitive pathways.

Insulin Syringe The standard syringe type used for subcutaneous peptide administration. Insulin syringes are available in 0.3ml, 0.5ml and 1ml sizes with fine gauge needles that minimise discomfort. Understanding how to read the unit markings on an insulin syringe is essential for accurate dosing.

Micrograms (mcg) The unit of measurement used for most peptide doses. One microgram is one thousandth of a milligram. Peptide doses are typically in the range of 100 to 500 micrograms per injection, though this varies considerably by compound.

Milligrams (mg) Used for peptides administered at higher doses, including TB-500, Semaglutide and Tirzepatide. One milligram equals 1,000 micrograms.

Loading Dose A higher initial dose used at the start of certain protocols to build up effective levels in the body more rapidly before transitioning to a standard maintenance dose. TB-500 protocols commonly use a loading phase.

Maintenance Dose The standard ongoing dose used after a loading phase, designed to sustain effective levels rather than build them. Lower than a loading dose and used for the duration of the main protocol period.

DAC (Drug Affinity Complex) A modification added to certain peptides, most commonly CJC-1295 — that significantly extends half-life by allowing the peptide to bind to albumin in the bloodstream. CJC-1295 with DAC has a half-life of 6 to 8 days, compared to 1 to 2 hours without it. The extended half-life changes both the dosing frequency and the nature of the GH release pattern it produces.

Certificate of Analysis (CoA) A laboratory document that verifies the purity, concentration and composition of a peptide product. A CoA from an independent third party laboratory is one of the most important quality indicators when evaluating a peptide source. It should confirm both the identity of the compound and its purity level — typically expressed as a percentage.

HPLC (High Performance Liquid Chromatography) One of the gold standard analytical methods used to verify peptide purity and composition. HPLC separates the components of a sample and identifies them by their chemical characteristics. A Certificate of Analysis that references HPLC testing provides meaningful assurance of product quality.

Mass Spectrometry (MS) Another gold standard analytical technique often used alongside HPLC. Mass spectrometry confirms the molecular weight and identity of a compound. HPLC/MS combined provides the most comprehensive verification of peptide identity and purity currently available.

Peptide Reconstitution Guide See the dedicated [Reconstitution Guide] in the Research & Science section for a step-by-step walkthrough of the reconstitution process, including equipment, volumes, mixing technique and storage.

Research and Science Terms

Research Grade Peptides produced and sold for research purposes rather than human clinical use. Research grade peptides are not approved pharmaceutical products and are not regulated in the same way. Quality varies significantly between suppliers — independent third-party testing through CoA documentation is the most reliable way to assess quality.

In Vitro Research conducted in a controlled laboratory environment, typically in cell cultures or test tubes rather than in living organisms. In vitro studies provide useful mechanistic information but do not directly demonstrate that effects will occur in the same way in a living human body.

In Vivo Research conducted in living organisms, most commonly rodents in peptide research, with some human studies available for certain compounds. In vivo results are more directly relevant than in vitro findings, but animal results do not always translate directly to human outcomes.

Human Clinical Trial A study conducted in human participants under controlled conditions. The gold standard for establishing the safety and effectiveness of any compound in humans. The number and quality of human clinical trials varies considerably across the peptide landscape; this site always distinguishes between compounds with robust human trial data and those primarily supported by animal or in vitro research.

Peer-Reviewed Research Scientific research that has been evaluated by independent experts in the relevant field before publication. Peer-reviewed studies carry significantly more weight than non-peer-reviewed sources, manufacturer claims or anecdotal reports.

Angiogenesis The formation of new blood vessels. Relevant to several peptides, particularly BPC-157, whose mechanisms include the promotion of angiogenesis as part of the tissue repair and healing process. New blood vessel formation improves the delivery of oxygen and nutrients to healing tissue.

Collagen Synthesis The production of collagen the most abundant structural protein in the body, is essential for skin integrity, tendon and ligament strength, bone matrix and wound healing. Several peptides support or stimulate collagen synthesis, including GHK-Cu and BPC-157.

Neuroplasticity The brain’s ability to form new neural connections, reorganise existing ones and adapt in response to experience or injury. Relevant to cognitive peptides such as Semax and Dihexa, whose research explores their potential to support or enhance neuroplastic processes.

BDNF (Brain-Derived Neurotrophic Factor) A protein that supports the survival, growth and maintenance of neurons. BDNF is associated with learning, memory and cognitive resilience. Semax is among the peptides researched for its ability to upregulate BDNF expression.

Telomere The protective cap at the end of each chromosome that shortens with each cell division. Telomere length is associated with cellular ageing shorter telomeres are linked to accelerated ageing and increased disease risk. Epithalon is among the peptides researched in relation to telomere biology.

Mitochondria The cellular structures responsible for producing the energy (ATP) that powers virtually all biological processes. Mitochondrial health and efficiency are increasingly understood as central to longevity, metabolic function and overall vitality. Peptides including MOTS-c and SS-31 are researched specifically for their effects on mitochondrial function.

Proteolysis The breakdown of proteins or peptides by enzymes. Proteolysis is the primary mechanism by which the body clears peptides from circulation — understanding it helps explain why half-life varies between compounds and why certain administration routes are more effective than others.

Individual Peptide Quick Reference

A brief description of each peptide covered on this site, with a link to its full library page for complete information on mechanisms, research, dosing and protocols.

AOD-9604 — A modified fragment of human growth hormone researched for its effects on fat metabolism and body composition. Unlike full growth hormone, it does not significantly affect IGF-1 levels. → [Full AOD-9604 page]

BPC-157 — Body Protection Compound 157. A 15 amino acid synthetic peptide derived from a protein found in human gastric juice. Among the most extensively researched peptides for tissue repair, gut health and inflammation. → [Full BPC-157 page]

CJC-1295 — A synthetic analogue of growth hormone-releasing hormone. Available with DAC for weekly dosing or without DAC for daily pulsatile administration. Commonly combined with Ipamorelin. → [Full CJC-1295 page]

Cerebrolysin — A peptide preparation derived from pig brain tissue, researched for neuroprotective and cognitive effects. → [Full Cerebrolysin page]

Dihexa — A nootropic peptide researched for its effects on cognitive function and neuroplasticity, including potential relevance to neurodegenerative conditions. → [Full Dihexa page]

DSIP — Delta Sleep Inducing Peptide. A naturally occurring neuropeptide researched for its effects on sleep architecture and growth hormone release. → [Full DSIP page]

Epithalon — A tetrapeptide researched for its effects on the pineal gland, melatonin production, telomere biology and longevity pathways. → [Full Epithalon page]

Follistatin 344 — A protein that inhibits myostatin, researched for its potential effects on muscle growth and body composition. → [Full Follistatin 344 page]

GHK-Cu — Glycine-Histidine-Lysine complexed with copper. One of the most researched peptides for skin health, collagen synthesis, wound healing and anti-ageing effects. → [Full GHK-Cu page]

GHRP-6 — Growth Hormone Releasing Peptide 6. Stimulates growth hormone release and also has appetite stimulating properties relevant to some protocols. → [Full GHRP-6 page]

GHRP-2 — Similar to GHRP-6 but with a stronger GH release effect and less appetite stimulation. → [Full GHRP-2 page]

Hexarelin — One of the most potent growth hormone releasing peptides, also researched for cardiovascular effects. → [Full Hexarelin page]

Humanin — A mitochondria-derived peptide researched for neuroprotective and metabolic effects. → [Full Humanin page]

IGF-1 LR3 — A modified form of Insulin-like Growth Factor 1 with an extended half-life. Researched for its effects on muscle growth, cellular repair and metabolism. → [Full IGF-1 LR3 page]

Ipamorelin — A selective growth hormone secretagogue known for producing a clean GH pulse without significantly affecting cortisol or prolactin. Commonly combined with CJC-1295. → [Full Ipamorelin page]

KPV — A tripeptide with researched anti-inflammatory and gut protective properties. Relevant to inflammatory bowel conditions and immune modulation. → [Full KPV page]

Larazotide — A peptide researched for its effects on intestinal permeability and gut barrier function. → [Full Larazotide page]

LL-37 — A naturally occurring antimicrobial peptide with immune modulating properties. → [Full LL-37 page]

Melanotan II — A synthetic analogue of alpha-melanocyte stimulating hormone, researched for effects on skin pigmentation, libido and appetite. → [Full Melanotan II page]

MGF — Mechano Growth Factor. A splice variant of IGF-1 produced in response to mechanical stress on muscle tissue. → [Full MGF page]

MOTS-c — A mitochondria-derived peptide researched for its effects on metabolic function, exercise performance and longevity. → [Full MOTS-c page]

NAD+ — Nicotinamide Adenine Dinucleotide. A coenzyme central to cellular energy production and mitochondrial function. While not a peptide in the traditional sense, it is increasingly incorporated into longevity and performance protocols alongside peptides. → [Full NAD+ page]

N-Acetyl Semax / N-Acetyl Selank — Modified versions of Semax and Selank with improved stability and bioavailability. → [Full pages]

PEG-MGF — A PEGylated form of MGF with an extended half-life, allowing more sustained activity in circulation. → [Full PEG-MGF page]

PT-141 (Bremelanotide) — A melanocortin receptor agonist researched for its effects on sexual function in both men and women. → [Full PT-141 page]

Retatrutide — A triple receptor agonist (GLP-1, GIP and glucagon) researched for weight loss and metabolic effects. One of the most significant emerging compounds in this space. → [Full Retatrutide page]

Selank — A synthetic heptapeptide developed from a fragment of human immunoglobulin. Researched for anxiolytic, nootropic and HPA axis modulating effects. → [Full Selank page]

Semax — A synthetic analogue of ACTH(4-10). Researched for cognitive enhancement, neuroprotection, BDNF upregulation and stress resilience. → [Full Semax page]

Semaglutide — A GLP-1 receptor agonist approved for type 2 diabetes and weight management. → [Full Semaglutide page]

SS-31 (Elamipretide) — A mitochondria-targeting peptide researched for its effects on mitochondrial function, cardiac health and cellular energetics. → [Full SS-31 page]

TB-500 — A synthetic version of Thymosin Beta-4 — specifically the active region responsible for its regenerative effects. Researched for systemic tissue repair, inflammation reduction and recovery. → [Full TB-500 page]

Tesofensine — A compound originally developed for Parkinson’s disease, subsequently researched for its effects on appetite and weight loss. → [Full Tesofensine page]

Thymosin Alpha-1 — A naturally occurring peptide produced by the thymus gland. Researched for immune system modulation and support. → [Full Thymosin Alpha-1 page]

Thymosin Beta-4 — A naturally occurring peptide involved in actin regulation, cellular repair and tissue regeneration. TB-500 is the synthetic version of its active region. → [Full Thymosin Beta-4 page]

Tirzepatide — A dual GLP-1 and GIP receptor agonist approved for type 2 diabetes and weight management. → [Full Tirzepatide page]

5-Amino-1MQ — A compound researched for its effects on metabolism through NNMT enzyme inhibition, with potential relevance to weight management. → [Full 5-Amino-1MQ page]

This glossary is updated as new compounds and terms are added to the site. If you encounter a term not covered here, visit the [FAQ] or use the site search to find relevant content.