Glossary

Plain language, defined.

Acetylated: A small chemical modification at the N-terminus that improves a peptide's stability and resistance to enzymatic breakdown.
Agonist: A molecule that activates a receptor, mimicking the body's natural signaling chemical.
Amino acid: The molecular building block of peptides and proteins. There are 20 standard amino acids in human biology.
AMPK: AMP-activated protein kinase. A cellular energy sensor activated by fasting, exercise, and several longevity peptides.
Angiogenesis: The formation of new blood vessels from existing ones — a key part of healing.
Antagonist: A molecule that blocks a receptor without activating it, preventing the natural ligand from binding.
Autophagy: Cellular self-cleaning — recycling damaged proteins and organelles. Stimulated by fasting, exercise, and some longevity peptides.
Bacteriostatic water: Sterile water with 0.9% benzyl alcohol, used to reconstitute lyophilized peptides.
BDNF: Brain-derived neurotrophic factor. Supports neuron growth and survival; widely targeted by nootropic peptides.
Bioavailability: The fraction of an administered dose that reaches systemic circulation in active form. Most peptides have very low oral bioavailability.
Blend: A pre-mixed combination of two or more peptides in a single vial (e.g. CJC-1295/Ipamorelin). Convenient but limits dosing flexibility.
Cardiolipin: A phospholipid concentrated in the inner mitochondrial membrane; required for ATP synthesis.
COA: Certificate of Analysis. A lab report showing the purity and identity of a peptide batch — non-negotiable for vetting suppliers.
Contraindication: A condition or factor that makes a particular treatment inadvisable or dangerous.
Cortisol: The body's main stress hormone. Some growth-hormone peptides (notably GHRP-6) can transiently raise it.
Cycling: Using a peptide for a defined period (e.g. 4-8 weeks) then resting to avoid receptor desensitization.
DAC: Drug Affinity Complex. A modification that binds CJC-1295 to albumin, extending its half-life from hours to days.
Desensitization: When receptors become less responsive after sustained signaling — the reason cycling matters.
Dipeptide: A peptide made of two amino acids.
Disulfide bridge: A covalent bond between two cysteine residues that locks a peptide into a folded shape; common in melanotan-class peptides.
DPP-4: Dipeptidyl peptidase-4. An enzyme that rapidly degrades many peptides including native GLP-1, motivating the use of resistant analogs.
Endogenous: Produced naturally inside the body — as opposed to exogenous compounds taken from outside.
Esterification: Adding an ester group to alter solubility or absorption (e.g. AC-262 357).
FDA approval: US regulatory clearance for human use. Many peptides discussed here are not FDA-approved and are sold for research use only.
FOXO3: A transcription factor linked to longevity and stress resistance; modulated by several longevity peptides.
Frontloading: Using a higher dose at the start of a cycle to reach steady-state concentrations faster.
GHRH: Growth hormone-releasing hormone. Tells the pituitary to release growth hormone.
GHRP: Growth hormone-releasing peptide — works through the ghrelin receptor to trigger a GH pulse.
GLP-1: Glucagon-like peptide-1. Slows gastric emptying and reduces appetite; the target of semaglutide and tirzepatide.
GIP: Glucose-dependent insulinotropic polypeptide. The second incretin hormone; co-targeted by tirzepatide and retatrutide.
Glucagon receptor: The third receptor agonised by retatrutide; activation boosts energy expenditure and lipolysis.
Half-life: Time it takes for half a dose to be cleared from circulation. Short half-life often means multiple daily doses.
HPLC: High-Performance Liquid Chromatography. The lab method used to confirm peptide purity on a COA.
IGF-1: Insulin-like growth factor 1. Downstream mediator of growth hormone effects on tissue.
Incretin: Gut hormones (GLP-1, GIP) released after eating that amplify insulin secretion.
Insulin sensitivity: How effectively cells respond to insulin. Higher is better for metabolic health.
Intranasal: Administered through the nose — bypasses first-pass metabolism and reaches the brain quickly. Used for Selank, Semax, and PT-141.
Ipamorelin pulse: A short, clean burst of growth hormone triggered by Ipamorelin without raising cortisol or prolactin.
Lipolysis: Breakdown of stored fat into free fatty acids and glycerol for use as energy.
Lyophilized: Freeze-dried. The form most research peptides ship in to remain stable until reconstituted.
Mass spec: Mass spectrometry — used on COAs to confirm the molecular weight and identity of a peptide.
MC1R / MC4R: Melanocortin receptors. MC1R drives skin pigmentation; MC4R is the central target for sexual arousal (PT-141).
mTOR: A central growth and nutrient sensor; chronic activation is linked to aging, while pulsed activation supports muscle protein synthesis.
NAD+: Nicotinamide adenine dinucleotide. A coenzyme essential for energy metabolism and sirtuin function.
NNMT: Nicotinamide N-methyltransferase. An enzyme that consumes NAD+ precursors; overexpressed in obesity.
Nootropic: A compound used to improve cognitive function — focus, memory, or stress resilience.
Off-label: Use of an approved drug for a purpose other than its FDA-approved indication.
Peptide: A short chain of amino acids (typically 2-50). Longer chains become proteins.
Pharmacokinetics: How a compound is absorbed, distributed, metabolized, and excreted by the body.
PT-141 flush: Facial flushing and brief nausea common with Bremelanotide (PT-141), due to MC1R cross-activation.
Pulsatile release: A short, sharp burst of hormone, closer to the body's natural rhythm than a sustained level.
Reconstitution: Mixing lyophilized peptide with bacteriostatic water to create an injectable solution.
Recombinant: Produced by bacteria or yeast engineered to express a human protein sequence.
Research use only: A label indicating the compound is sold for laboratory research and not approved for human consumption.
Sirtuins: A family of NAD+-dependent enzymes (SIRT1-7) involved in longevity and stress response.
Slow-wave sleep: The deepest stage of non-REM sleep — when most physical recovery and GH release occur.
Stack: A combination of compounds used together to target complementary mechanisms.
Subcutaneous: Beneath the skin. The standard injection route for most peptides.
Telomere: Protective caps on chromosomes that shorten with each cell division; targeted by longevity-focused peptides.
Titration: Gradually increasing dose over weeks to minimize side effects — standard for GLP-1 class peptides.
WADA: World Anti-Doping Agency. Many peptides on this site are on its prohibited list — relevant for tested athletes.
Z-track: An injection technique that displaces skin sideways to prevent the drug from tracking back out — used for oil-based IM injections.