Educational content only. Not medical advice. The content creators are not doctors or medical professionals. Consult your healthcare provider before taking any action.
Peptide Glossary: 100+ Terms Defined
Category: Beginner Type: Glossary Read Time: 15 minutes Author: Peptides.NYC Editorial Last Updated: 2026-04-08 URL: https://peptides.nyc/learn/peptide-glossary
Overview
From amino acids to zetapeptides, every term you need to know. Searchable reference for peptide terminology.
A
Amino Acid - The building blocks of peptides and proteins. There are 20 standard amino acids used in human biology.
Anabolic - Relating to the building up of complex molecules in the body, particularly muscle tissue.
Antimicrobial Peptide (AMP) - Peptides that can kill or inhibit the growth of microorganisms like bacteria, fungi, and viruses.
AOD-9604 - A modified fragment of human growth hormone (amino acids 176-191) studied for fat metabolism.
B
Bacteriostatic Water (BAC Water) - Sterile water containing 0.9% benzyl alcohol used to reconstitute peptides. Prevents bacterial growth.
Bioavailability - The proportion of a substance that enters circulation and is available for use by the body.
BPC-157 - Body Protection Compound-157, a synthetic peptide derived from a protein in gastric juice, studied for healing properties.
Buffer - A solution that maintains stable pH, often used in peptide formulations.
C
Cathelicidin - A family of antimicrobial peptides; LL-37 is the human cathelicidin.
CJC-1295 - A synthetic growth hormone-releasing hormone (GHRH) analog with extended half-life.
Compounding Pharmacy - A pharmacy that creates customized medications, including peptides, based on prescriptions.
COA (Certificate of Analysis) - Document from a lab verifying the purity and composition of a peptide.
Cyclic Peptide - A peptide where the amino acid chain forms a ring structure.
D
DAC (Drug Affinity Complex) - A modification added to CJC-1295 that extends its half-life significantly.
DSIP (Delta Sleep-Inducing Peptide) - A neuropeptide that modulates sleep architecture.
Desensitization - Reduced response to a peptide after prolonged use.
E
Epithalon - A tetrapeptide (Ala-Glu-Asp-Gly) that may activate telomerase.
Endogenous - Produced naturally within the body.
Exogenous - Introduced from outside the body.
F
Follistatin - A protein that inhibits myostatin, potentially allowing for increased muscle growth.
Fragment - A portion of a larger peptide or protein, like HGH Fragment 176-191.
G
GH (Growth Hormone) - A peptide hormone produced by the pituitary gland, essential for growth and metabolism.
GHRH (Growth Hormone-Releasing Hormone) - A hormone that stimulates the pituitary to release GH.
GHRP (Growth Hormone-Releasing Peptide) - Synthetic peptides that stimulate GH release via the ghrelin receptor.
GHK-Cu - A tripeptide naturally found in plasma that has regenerative properties when complexed with copper.
GLP-1 (Glucagon-Like Peptide-1) - A hormone involved in blood sugar regulation and appetite control.
Ghrelin - The "hunger hormone" that also stimulates GH release.
H
Half-Life - The time it takes for half of a substance to be eliminated from the body.
Hexarelin - A potent GHRP with cardioprotective properties.
HPLC (High-Performance Liquid Chromatography) - A testing method used to verify peptide purity.
HGH (Human Growth Hormone) - The naturally occurring growth hormone in humans.
I
IGF-1 (Insulin-Like Growth Factor 1) - A hormone with anabolic effects, stimulated by GH.
Ipamorelin - A selective GHRP known for minimal side effects.
Intramuscular (IM) - Injection into muscle tissue.
Intranasal - Administration through the nose.
K
Kisspeptin - A peptide that regulates reproductive hormones (LH and FSH).
KPV - A tripeptide fragment of alpha-MSH with anti-inflammatory properties.
L
LL-37 - Human cathelicidin antimicrobial peptide.
Lyophilized - Freeze-dried; the form most peptides come in before reconstitution.
Loading Phase - Initial higher-dose period to achieve therapeutic levels quickly.
M
Mass Spectrometry (MS) - Testing method to confirm molecular weight and identity of peptides.
MCG (Micrograms) - Unit of measurement; 1000 mcg = 1 mg.
Melanotan - Peptides (MT-I and MT-II) that stimulate melanin production.
Mod GRF 1-29 - Another name for CJC-1295 without DAC.
MOTS-c - A mitochondrial-derived peptide involved in metabolic regulation.
Myostatin - A protein that limits muscle growth; inhibiting it may increase muscle mass.
N
Neuropeptide - Peptides that act as neurotransmitters or neuromodulators.
N-terminus - The end of a peptide chain with a free amino group.
O
Off-Label - Use of a medication for purposes other than its FDA-approved indication.
Oral Bioavailability - The degree to which an orally administered substance reaches circulation.
P
Peptide Bond - The chemical bond between amino acids in a peptide chain.
Pituitary - The "master gland" that produces many hormones including GH.
Polypeptide - A longer chain of amino acids (10-50+), sometimes used interchangeably with "peptide."
PT-141 (Bremelanotide) - A melanocortin receptor agonist used for sexual dysfunction.
Pulsatile - Release in pulses rather than continuously (natural GH release pattern).
R
Reconstitution - The process of mixing lyophilized peptide with bacteriostatic water.
Receptor - A protein on cell surfaces that peptides bind to, triggering biological effects.
ROA (Route of Administration) - How a substance is delivered (subcutaneous, intramuscular, nasal, oral, etc.).
S
Secretagogue - A substance that promotes the secretion of another substance (e.g., GH secretagogue).
Semax - A synthetic peptide derived from ACTH with nootropic properties.
Selank - A synthetic peptide with anxiolytic and nootropic effects.
Semaglutide - A GLP-1 agonist used for diabetes and weight management (Ozempic, Wegovy).
Subcutaneous (SubQ) - Injection under the skin, into fatty tissue.
T
TB-500 (Thymosin Beta-4) - A naturally occurring peptide involved in tissue repair.
Tesamorelin - An FDA-approved GHRH analog for reducing visceral fat.
Telomere - Protective caps on chromosomes; their length is associated with aging.
Tirzepatide - A dual GIP/GLP-1 agonist for diabetes and weight loss (Mounjaro, Zepbound).
Thymosin Alpha-1 - An immune-modulating peptide derived from the thymus.
V
VIP (Vasoactive Intestinal Peptide) - A peptide used in treating CIRS (Chronic Inflammatory Response Syndrome).
Vial - Container for lyophilized peptides.
Z
Zonulin - A protein that regulates intestinal permeability (related to "leaky gut").
Units Quick Reference
| Unit | Equivalent |
|---|---|
| 1 mg | 1000 mcg |
| 1 ml | 1 cc |
| 1 IU (insulin) | Varies by compound |
Related Content
Disclaimer: This content is for educational purposes only and is not medical advice. Consult a healthcare provider before starting any peptide protocol.
Source: https://peptides.nyc/learn/peptide-glossary
Frequently asked questions
What is the difference between a peptide and a protein?
It is a length question, not a kind question. Both are chains of amino acids linked by peptide bonds. By common biochemistry convention, chains of roughly 50 or fewer amino acids are called peptides; longer chains are called proteins. Practically, peptides used therapeutically are usually 5-40 amino acids long, which is short enough to manufacture synthetically.
What does "amino acid sequence" mean?
It is the specific order of amino acids in a peptide chain, written N-terminus to C-terminus. Sequence determines how the peptide folds, what receptors it binds, and what it does. Changing a single amino acid can dramatically change activity — that is why peptide analogs (semaglutide vs natural GLP-1, for example) behave differently from the natural hormone.
What is a peptide bond?
The chemical link between two amino acids — formed when the carboxyl group of one amino acid reacts with the amino group of another and releases a molecule of water. It is the structural backbone of every peptide and protein.
What does "lyophilized" mean?
It means freeze-dried. Lyophilization removes water by sublimation under vacuum, leaving a stable powder. Most research and prescription peptides ship lyophilized because the dry form is far more stable in transit and storage. You add bacteriostatic water at the point of use ("reconstitution") to make the working solution.
What is a COA?
A Certificate of Analysis — a batch-specific document from the manufacturer (or a third-party lab) confirming the peptide's identity, purity, and absence of contaminants. Reputable vendors publish batch-level COAs for every product. Absence of a COA is a major red flag.
Written By
Editorial team. We cite published research; we are not licensed clinicians and content is not medically reviewed.
This article cites peer-reviewed research and medical literature. Click any reference to view the original source.
- 1
Lau JL, Dunn MK (2018) Therapeutic peptides: Historical perspectives, current development trends, and future directions Bioorganic & Medicinal Chemistry.
- 2
Fosgerau K, Hoffmann T (2015) Peptide therapeutics: current status and future directions Drug Discovery Today.
- 3
Chen D, Rehfeld JF, Watts AG, et al. (2023) History of key regulatory peptide systems and perspectives for future research Journal of Neuroendocrinology.
Medical Disclaimer
The information on this website is for educational purposes only and is not medical advice. The content creators are not doctors or medical professionals. This content should not be used to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare provider before starting any new supplement, medication, or health protocol. You assume all risks associated with using this information.