Reference

Peptide Glossary

Plain-language definitions of the terms you’ll run into when reconstituting and dosing peptides — from bacteriostatic water and U-100 units to half-life, titration, and blends. Pairs with our peptide calculator and education library.

Last updated August 2026

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A B C D E F G H I L M N P R S T U V W

Acetate salt: The form most synthetic peptides are supplied in — the peptide bound to acetic acid. It affects the exact peptide mass by weight. A related form, the TFA (trifluoroacetate) salt, is common in early research material.
Agonist: A molecule that activates a receptor to produce a response. Many peptides are receptor agonists — GLP-1 agonists, for example, switch on the GLP-1 receptor.
Amino acid: The building blocks of peptides and proteins. A peptide is a short chain of amino acids linked together; the specific sequence determines what the peptide does.
Amylin: A hormone released alongside insulin that slows gastric emptying and reduces appetite. Amylin analogs such as cagrilintide and pramlintide are studied for metabolic and weight effects.
Anabolic: Describes processes that build tissue, such as muscle-protein synthesis. Several peptides are discussed in an anabolic context, though “anabolic” here does not mean an anabolic steroid.
Angiogenesis: The growth of new blood vessels. Peptides like BPC-157 are studied partly because they appear to promote angiogenesis, which supports tissue repair by improving blood supply.
Antagonist: A molecule that blocks a receptor rather than activating it, preventing the normal signal. The opposite of an agonist.
Aseptic technique: The practice of keeping everything sterile while reconstituting and drawing — wiping stoppers with alcohol, not touching needle tips — to avoid contaminating the vial.
Bacteriostatic water · also “bac water”: Sterile water containing 0.9% benzyl alcohol, which inhibits bacterial growth so a reconstituted multi-dose vial stays usable for longer (commonly up to ~28 days refrigerated). The standard diluent for lyophilized peptides.
Benzyl alcohol: The 0.9% preservative in bacteriostatic water. It’s what makes the water “bacteriostatic” — allowing a vial to be used for multiple doses over weeks rather than once.
Bioavailability: The fraction of a dose that reaches circulation in active form. Injected peptides have high bioavailability; most peptides are poorly absorbed if swallowed, which is why they are usually injected.
Bioregulator: A very short peptide proposed to influence gene expression in a specific tissue. The Khavinson “bioregulator” peptides come from largely non-Western research with limited replication.
Certificate of Analysis (COA) · also “COA”: A lab report stating a peptide’s identity and purity, typically from HPLC and mass spectrometry. A legitimate COA ties to a specific batch. See our guide on how to read a COA.
Collagen: The main structural protein in skin, tendon and connective tissue. Peptides such as GHK-Cu are studied for supporting collagen synthesis and remodeling.
Concentration: How much peptide is in each millilitre of solution after reconstitution — calculated as vial amount (mg) ÷ water added (mL). More water means a weaker (more dilute) solution and more units to draw per dose.
Cycle · also “cycling”: A defined period of use followed by a break. Cycling peptides is commonly discussed to manage receptor sensitivity and structure a protocol, though evidence for specific schedules is limited.
Cytoprotective: Describes something that protects cells from damage. BPC-157 is often described as cytoprotective in animal studies.
DAC (Drug Affinity Complex) · also “DAC”: A modification (as in “CJC-1295 with DAC”) that lets a peptide bind albumin in the blood, extending its half-life from hours to days. The “no-DAC” version acts more briefly.
Dead space: The small volume of liquid left in the needle and syringe hub after injecting. Insulin syringes with a fixed (non-removable) needle have very little dead space, which reduces waste.
Diluent: The liquid used to reconstitute a lyophilized peptide — usually bacteriostatic water. It dissolves the powder so it can be drawn and measured.
Dose · also “dosage”: The amount of peptide taken at one time, usually given in micrograms (mcg) or milligrams (mg). This is different from the number of units you draw, which also depends on your concentration.
Doses per vial: How many individual doses a reconstituted vial contains — total peptide ÷ dose per injection. For example, a 5 mg (5,000 mcg) vial at a 250 mcg dose gives 20 doses.
Downregulation · also “desensitization”: When repeated stimulation makes cells reduce their receptors or responsiveness, blunting a peptide’s effect over time. A reason cycling and dose breaks are discussed.
Excipient: An inactive ingredient included with a peptide for stability or handling — for example mannitol used as a bulking agent in some lyophilized vials.
Frontloading: Taking a larger initial dose to reach a target level in the body faster, before settling into a regular maintenance dose. Often discussed with longer-half-life compounds.
Ghrelin: The “hunger hormone,” which also stimulates growth-hormone release. GHRPs and secretagogues like Ipamorelin act on the ghrelin (GHS) receptor.
GHRH · also “growth hormone releasing hormone”: Peptides like Sermorelin, CJC-1295 and Tesamorelin that mimic the body’s own growth-hormone-releasing hormone. Often discussed alongside GHRPs, which act on a different receptor.
GHRP · also “growth hormone releasing peptide”: A class of peptides (e.g. GHRP-2, GHRP-6, Ipamorelin, Hexarelin) that signal the pituitary gland to release growth hormone.
GIP: Glucose-dependent insulinotropic polypeptide, a gut hormone involved in insulin release. Dual agonists like tirzepatide act on both the GIP and GLP-1 receptors.
GLP-1: Glucagon-like peptide-1, a hormone that influences blood sugar and appetite. GLP-1 receptor agonists (e.g. semaglutide, tirzepatide) are the class behind many metabolic/weight compounds.
Glucagon: A hormone that raises blood sugar and increases energy expenditure. Newer triple agonists such as retatrutide add glucagon-receptor activity to GLP-1/GIP effects.
Half-life: How long it takes for half of a peptide to clear from the body. A short half-life may mean more frequent dosing; a long one may allow less frequent dosing.
HPLC purity: A peptide’s percentage purity measured by high-performance liquid chromatography — the most-cited purity figure on a COA. A higher value (e.g. >98%) indicates fewer impurities.
IGF-1: Insulin-like growth factor 1, a hormone downstream of growth hormone that mediates many of its growth effects. Analogs like IGF-1 LR3 are studied in a muscle-growth context.
Injection site rotation: Alternating where you inject (for example different areas of the abdomen) to avoid irritation, lumps or tissue damage from repeatedly using one spot.
Insulin syringe: A small syringe marked in insulin “units” rather than millilitres, used to draw and inject reconstituted peptides. Common barrel sizes are 30, 50, and 100 units.
International Unit (IU): A measure of biological activity used for some substances (like HCG or HGH) instead of mass. It is not interchangeable with insulin “units” on a syringe.
Intramuscular (IM): An injection into muscle tissue, deeper than subcutaneous. Less common for research peptides, which are typically subcutaneous.
Intranasal: Administration as a nasal spray. Some peptides, such as Semax and Selank, are commonly used intranasally rather than by injection.
Loading dose: A larger dose at the start of a protocol to reach target levels faster, sometimes used with longer-half-life compounds before switching to a maintenance dose. See also frontloading.
Lyophilized · also “freeze-dried”: A peptide that has been freeze-dried into a stable powder for shipping and storage. It must be reconstituted with bacteriostatic water before it can be drawn and dosed.
Mass spectrometry: A lab technique that confirms a peptide’s molecular weight, verifying it is the right molecule. It is usually reported alongside HPLC purity on a COA.
Melanocortin: A family of receptors involved in pigmentation, appetite and sexual function. Melanotan and PT-141 act on melanocortin receptors.
Microgram (mcg) · also “µg”: A unit of mass equal to one-millionth of a gram. 1 milligram (mg) = 1,000 micrograms (mcg). Many peptide doses are given in mcg while vials are labelled in mg.
Milligram (mg): A unit of mass equal to one-thousandth of a gram. Peptide vials are usually labelled in mg; converting your mg vial and mcg dose to the same unit is the first step in any calculation.
Needle gauge: The thickness of a needle; a higher gauge is thinner. Insulin syringes for subcutaneous peptide injections are typically fine (high-gauge, e.g. 29–31G) for comfort.
Net peptide content: The actual peptide mass in a vial after accounting for bound water and salt (such as acetate). It can be somewhat lower than the labelled amount, which matters for precise dosing.
Nootropic: A substance used with the aim of supporting cognition, focus or memory. Peptides like Semax and Selank are discussed as nootropics, though human evidence varies.
Peptide bond: The chemical link joining one amino acid to the next. A chain of amino acids connected by peptide bonds is what makes a peptide.
Peptide sequence: The specific order of amino acids in a peptide, usually written as three-letter codes (e.g. Gly-Glu-Pro…). The sequence determines the peptide’s shape and activity.
Pituitary gland: A small gland at the base of the brain that releases growth hormone and other hormones. GHRH and GHRP peptides work by signaling the pituitary.
Pulsatile release: Hormone release in bursts rather than a steady stream. Growth hormone is released in pulses, which is why GH-secretagogue timing is discussed.
Receptor: A protein, usually on a cell surface, that a peptide or hormone binds to in order to trigger an effect. Which receptor a peptide targets largely defines what it does.
Reconstitution: Mixing a lyophilized (freeze-dried) peptide with bacteriostatic water so it dissolves into a liquid you can measure and inject. How much water you add sets the concentration.
Reconstitution ratio: The relationship between peptide amount and water added (e.g. 5 mg in 2 mL). Changing it doesn’t change your dose — only how many units you draw for that dose.
Research chemical: A compound sold for laboratory research rather than human use. Most peptides on this site fall in this category and are not approved medicines — a key reason all content here is educational.
Secretagogue: A substance that prompts the body to secrete something. Growth-hormone secretagogues (like GHRPs) trigger the body’s own growth hormone release rather than supplying hormone directly.
Sharps container: A puncture-resistant container for safely disposing of used needles and syringes, rather than putting them in regular trash.
Stack · also “blend”: Using more than one peptide together. A “blend” specifically means multiple peptides premixed in a single vial (e.g. BPC-157/TB-500), so each draw contains a fixed ratio of each.
Sterile water: Preservative-free water for injection. Unlike bacteriostatic water it contains no benzyl alcohol, so a vial reconstituted with it is meant for single use rather than repeated draws over weeks.
Subcutaneous (SubQ): An injection into the fatty layer just under the skin — the most common route for research peptides, typically with a short insulin needle.
Tachyphylaxis: A rapid drop in response after repeated doses over a short period — a faster form of tolerance. Sometimes discussed with frequently dosed peptides.
Titration: Gradually adjusting a dose over time — usually starting low and increasing in steps — to reach a target while gauging tolerance. Common with metabolic (GLP-1) compounds.
U-100: The standard insulin-syringe scale where 100 units equals 1 millilitre. Nearly all insulin syringes used for peptides are U-100.
Unit · also “insulin unit”: The graduated markings on an insulin syringe. On a U-100 syringe, 100 units = 1 mL, so each unit is 0.01 mL. Units measure volume, not a fixed amount of peptide.
Vasodilation: Widening of blood vessels, which increases blood flow. Some peptides influence vasodilation via the nitric-oxide pathway.
Vial: The small sealed glass bottle a lyophilized peptide comes in. You inject bacteriostatic water through its rubber stopper to reconstitute, then draw doses from it.
WADA · also “World Anti-Doping Agency”: The World Anti-Doping Agency, which bans many peptides (e.g. BPC-157, GH secretagogues) in competitive sport. Athletes subject to testing should assume these are prohibited.

Educational reference only — not medical advice. Always follow the guidance of a qualified healthcare professional.