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Peptide Glossary

Plain-English definitions of the terms you’ll meet reading about peptides.

The basics

Amino acid: The organic building block that chains together to form peptides and proteins. The human body uses 20 standard amino acids, sorted into three groups: essential (must come from food — the body can't make them), nonessential (the body makes on its own), and conditional (normally nonessential but needed in larger amounts during illness or stress). They also build tissue, hormones, neurotransmitters, and immune antibodies.
Peptide: A short chain of amino acids — typically 2 to around 50. Beyond that length the chains fold into what we call proteins, so peptides are the smaller cousins. A peptide's identity and effects come from which amino acids it contains and in what order.
Peptide bond: The chemical link that joins two amino acids into a chain. It forms when the carboxyl group of one amino acid reacts with the amino group of the next, releasing a molecule of water. Repeated peptide bonds are the backbone of every peptide and protein.
Sequence: The exact order of amino acids in a peptide — its molecular identity. Change the order and you change the molecule: BPC-157 and TB-500 are different peptides precisely because their sequences differ, which is why they're studied for different things.

Use & administration

Bacteriostatic water: Sterile water containing a small amount of preservative (usually 0.9% benzyl alcohol). It's used to reconstitute lyophilized peptides for multi-dose vials because the preservative slows bacterial growth once the vial is punctured. Single-dose vials instead use plain sterile water.
Cycle: A defined period of use followed by a planned break — for example a 4-week cycle. 'Cycling' is community practice drawn from bodybuilding and anti-aging forums, not an established medical protocol, and the optimal lengths (if any) aren't well studied.
Intramuscular (IM): An injection delivered into a muscle (common sites: deltoid, glute, thigh). Less common than SubQ for peptides; absorption can be faster but it tends to be more uncomfortable.
Reconstitution: Mixing a lyophilized (freeze-dried) peptide powder with a sterile solvent — almost always bacteriostatic water — to turn it into a measurable injectable solution. The total volume of solvent determines the concentration per unit on an insulin syringe.
Subcutaneous (SubQ): An injection into the fatty tissue just beneath the skin (common sites: abdomen, thigh). It's the most common route for injectable peptides because it's easy to self-administer, low pain, and absorbs steadily.

Categories you'll see here

Copper peptide (GHK-Cu): A peptide complexed with a copper ion (GHK is the peptide sequence, Cu is the copper). Researched for skin, collagen, and tissue-repair effects and used topically in many skincare products as well as studied in research contexts.
GHRP / GHRH: Growth-hormone-releasing peptides (GHRP) and growth-hormone-releasing hormones (GHRH) — two classes that each stimulate the body's own growth-hormone pathway through different receptors (e.g. ipamorelin is a GHRP, CJC-1295 is a GHRH analog). They're often discussed, and sometimes combined, in research on GH support.
GLP-1: Glucagon-like peptide-1 — an incretin hormone pathway involved in insulin release and appetite. It's the target of approved medicines such as semaglutide (Ozempic/Wegovy) and tirzepatide (Mounjaro/Zepbound), used for diabetes and weight management.
Secretagogue: A substance that prompts the body to release something. A growth-hormone secretagogue, for instance, signals the body to release more of its own GH rather than supplying GH directly.

Quality & sourcing

COA (Certificate of Analysis): A lab report confirming what's actually in a batch — typically the peptide's identity and purity, sometimes quantified by method (e.g. HPLC). Only a third-party (independent) COA is meaningful; a vendor's in-house lab has a built-in conflict of interest and isn't independent verification.
Lyophilized: Freeze-dried into a dry powder. It's the stable, shippable form most research peptides come in — dehydrated for shelf life, then reconstituted with bacteriostatic water before use.
Purity: The fraction of the sample that is the stated peptide — e.g. '99%+ pure' — as measured on the COA (usually by HPLC). Purity is about how much of the powder is the right molecule, which is distinct from whether it's sterile, endotoxin-free, or accurately dosed.
Research chemical: The legal label under which most peptides are sold — 'for research use only, not for human consumption.' This is the category that allows them to be sold at all, and it's also exactly why buyers should be cautious: the label means no assurance of human-grade quality, sterility, or dosing accuracy.

Keep going

Now that the vocabulary’s clear, learn how to read a study or browse specific peptides.

Educational content only. The Health Stacks does not provide medical advice. Peptides discussed on this site are not FDA-approved for human use unless explicitly stated. Always consult a qualified healthcare professional before use.