● GLOSSARY31 TERMS · DEFINED

The glossary.

Key terms used in peptide science and research — the jargon you’ll run into across profiles, forum threads, and the primary literature. Jump to a letter, or scroll.

§ A

3 terms

Amino Acid: Organic molecules that serve as the building blocks of peptides and proteins. There are 20 standard amino acids encoded by DNA.
Amphipathic: Having both hydrophilic and hydrophobic regions. Many antimicrobial peptides like LL-37 have amphipathic structures that insert into cell membranes.
Angiogenesis: Formation of new blood vessels from existing ones. Peptides like BPC-157 and TB-500 promote angiogenesis for wound healing and tissue repair.

§ B

3 terms

Bioavailability: The proportion of a substance that enters systemic circulation. Subcutaneous injection typically offers higher bioavailability than oral administration for peptides.
Bioregulator: Short peptides (2-4 amino acids) that regulate gene expression at the epigenetic level. Term coined by Vladimir Khavinson. Examples: Epithalon, Thymalin.
BDNF: Brain-Derived Neurotrophic Factor. Supports neuronal survival, growth, and plasticity. Increased by peptides like Semax, Selank, and Dihexa.

§ C

4 terms

CAS Number: Chemical Abstracts Service registry number — a unique identifier for chemical substances, used to unambiguously identify peptide compounds.
Cathelicidin: A family of antimicrobial peptides. LL-37 is the only human cathelicidin, part of the innate immune system and regulated by vitamin D.
Compounding Pharmacy: A pharmacy that creates customized medications. 503A pharmacies serve individuals; 503B facilities produce larger batches under FDA oversight.
Cycling: Using a peptide for a defined period followed by a break (e.g., 8 weeks on, 4 off). Prevents receptor desensitization and maintains effectiveness.

§ D

2 terms

Dalton (Da): Unit of molecular mass. Peptides range from ~300 Da (tripeptides) to ~5,000 Da. Proteins are generally over 10,000 Da.
Desensitization: Reduced receptor responsiveness after prolonged agonist exposure. Hexarelin causes GHS-R1a desensitization, requiring cycling.

§ G

4 terms

GH (Growth Hormone): A 191-amino-acid peptide hormone from the anterior pituitary. Many peptides (Ipamorelin, CJC-1295, Hexarelin) stimulate natural GH release.
GHRH: Growth Hormone-Releasing Hormone. A hypothalamic peptide stimulating GH synthesis and release. CJC-1295 and Sermorelin are synthetic GHRH analogs.
GHRP: Growth Hormone Releasing Peptide. Synthetic peptides activating the ghrelin receptor to release GH. Examples: Ipamorelin, Hexarelin.
GLP-1: Glucagon-Like Peptide-1. An incretin hormone regulating appetite and blood sugar. Semaglutide, liraglutide, and tirzepatide are GLP-1 agonists.

§ H

2 terms

Half-life: Time for a substance's concentration to decrease by half. Determines dosing frequency — from minutes (Semax) to days (semaglutide).
HPG Axis: Hypothalamic-Pituitary-Gonadal Axis. The hormonal feedback loop controlling reproductive hormones. Kisspeptin is its master upstream regulator.

§ I

1 term

IGF-1: Insulin-like Growth Factor 1. Produced by the liver in response to GH. Mediates many anabolic effects including muscle growth.

§ L

1 term

Lyophilization: Freeze-drying process preserving peptides as powder. Must be reconstituted with bacteriostatic water before injection.

§ M

2 terms

Melanocortin Receptor: G-protein coupled receptors (MC1R-MC5R) binding melanocortins. MC1R controls pigmentation, MC4R affects appetite and sexual arousal.
Mitochondrial-Derived Peptide: Peptides encoded by mitochondrial DNA. MOTS-c and Humanin are the most studied, linking mitochondrial function to metabolism.

§ N

1 term

NF-kB: Nuclear Factor kappa B. A master transcription factor controlling inflammation. Inhibited by anti-inflammatory peptides like KPV.

§ P

2 terms

Peptide: A short chain of amino acids (typically 2-50) linked by peptide bonds. Smaller than proteins. Function as hormones, neurotransmitters, and growth factors.
Peptide Bond: The covalent bond between two amino acids, formed when one's carboxyl group reacts with another's amino group, releasing water.

§ R

1 term

Reconstitution: Dissolving lyophilized peptide powder in bacteriostatic water. Gentle swirling (not shaking) preserves peptide integrity.

§ S

2 terms

Secretagogue: A substance promoting secretion. Growth hormone secretagogues stimulate the pituitary to release GH. Examples: Ipamorelin, Hexarelin, CJC-1295.
Subcutaneous Injection: Injection into fatty tissue between skin and muscle. The most common peptide administration route, using short insulin-type needles.

§ T

3 terms

Telomerase: Enzyme adding telomeric repeat sequences to chromosome ends, counteracting age-related shortening. Activated by Epithalon.
Telomere: Protective DNA caps at chromosome ends. Shorten with each cell division. Length is considered a biomarker of biological aging.
Titration: Gradually adjusting dosage to find the optimal dose while minimizing side effects. Most peptide protocols start low and titrate upward.

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