Glossary

Terms you'll see.

Plain-English definitions for the medical abbreviations, hormones, and jargon that show up across the library. Skim before diving in. Linked automatically the first time each term appears on a peptide page.

47 terms.

Agonist: A molecule that binds to a receptor and activates it — the receptor responds as if its natural ligand bound.
Anabolicalso: anabolism: Building tissue — muscle, bone, collagen. Opposite of catabolic (breaking down). GH and IGF-1 are anabolic signals.
Angiogenesis: Growth of new blood vessels. Healing peptides like BPC-157 use angiogenesis to bring repair crews (blood, oxygen, nutrients) to injury sites.
Antagonist: A molecule that binds to a receptor without activating it, blocking the natural ligand from binding.
Anxiolytic: Anti-anxiety effect. Selank is a peptide anxiolytic that doesn't sedate like benzodiazepines do.
Autophagy: "Self-eating" — your cells recycle damaged parts. Triggered by fasting, exercise, and some peptides. Considered a key longevity mechanism.
Bacteriostatic Water (BAC)also: bacteriostatic water, BAC water: Sterile water with 0.9% benzyl alcohol added as a preservative. Used to reconstitute lyophilized peptides; safe to use the same vial for ~28 days.
Bioavailability: The fraction of a dose that actually reaches systemic circulation. Subcutaneous injection ≈ 50–100%; oral peptides usually <2%.
C-cell tumoralso: medullary thyroid carcinoma, MTC: A rare thyroid cancer originating from calcitonin-producing C-cells. GLP-1 drugs carry an FDA black-box warning for it (based on rat studies; human risk is uncertain but the warning is mandatory).
C-max: Peak concentration in blood after a dose.
Clinical trial phases: Phase 1 = safety in small healthy group. Phase 2 = efficacy + dose finding. Phase 3 = large-scale efficacy vs standard. Phase 4 = post-approval surveillance.
Compounding pharmacy: A pharmacy that prepares custom medications. In the US, 503A compounding is for individual prescriptions; 503B is bulk for clinics.
DACalso: drug affinity complex: Drug Affinity Complex. A chemical tag that binds the peptide to blood albumin so it lasts way longer in your body. CJC-1295 with DAC = weekly dose; without DAC = daily.
Fastedalso: fasting state: Empty stomach — at least 3 hours since your last meal. Many peptides (GH-releasers especially) work much better fasted because insulin blunts the response.
Ghrelin: Your "hunger hormone" — released by the stomach when empty, signals the brain to eat. Some peptides activate the ghrelin receptor to trigger GH release (with hunger as a side effect).
GHRHalso: growth hormone releasing hormone: Growth Hormone Releasing Hormone. Your brain's signal to release GH. Sermorelin, CJC-1295, and Tesamorelin mimic this signal.
GHRPalso: growth hormone releasing peptide: Growth Hormone Releasing Peptide. A different signal that ALSO triggers GH release (via the ghrelin receptor). Ipamorelin is a GHRP. Stacking GHRH + GHRP gives the biggest GH pulse.
GIP: Glucose-dependent insulinotropic polypeptide. An incretin hormone like GLP-1; tirzepatide is a dual GLP-1/GIP agonist.
GLP-1 agonist: A compound that activates the GLP-1 receptor — increases insulin, slows gastric emptying, suppresses appetite. Examples: semaglutide, tirzepatide, retatrutide.
Glucagon receptor: Receptor whose activation increases hepatic glucose output and energy expenditure. Retatrutide hits this in addition to GLP-1/GIP.
Growth Hormonealso: GH, hGH, human growth hormone: The pituitary hormone that drives growth in kids and tissue repair in adults. Peptides like Ipamorelin and Sermorelin tell your body to make more of its own GH.
Half-lifealso: half-life, t½: Time for blood concentration to drop by half. Determines dose frequency. Sema/reta ≈ 1 week; BPC-157 ≈ minutes (in vitro).
HPG axisalso: hypothalamic-pituitary-gonadal axis: Hypothalamus → Pituitary → Gonads (testes/ovaries). The hormonal chain that controls testosterone and estrogen production. Kisspeptin and AAS both act on it.
IGF-1: Insulin-like growth factor 1. Liver makes it in response to growth hormone; mediates most of GH's anabolic effects.
Incretin: A gut hormone released when you eat. GLP-1 and GIP are incretins — they tell the pancreas to release insulin and the brain that you're full.
Insulin resistance: When your cells stop responding well to insulin's "absorb the sugar" signal. Leads to high blood sugar, fat storage, and eventually type 2 diabetes.
Intramuscularalso: IM, intramuscular: Injection directly into a muscle (deltoid, quad, glute). Faster absorption than SubQ; used when you need quicker onset or for oily compounds.
Intravenousalso: IV, intravenous: Injection directly into a vein. 100% bioavailability, immediate effect. Almost always a clinic-only route.
IUalso: international unit: International Unit. A standardized activity measurement, not a weight. Used for HGH and insulin because batch potency varies.
Lyophilized: Freeze-dried. How most peptides ship — stable as a powder, must be reconstituted with sterile water before injection.
mcgalso: microgram, micrograms: Microgram. 1/1000 of a milligram. Many peptides are dosed in mcg because they're potent at tiny amounts (e.g. 250 mcg = 0.25 mg).
Melanocortin receptoralso: MC1R, MC2R, MC3R, MC4R, MC5R: A family of 5 receptors (MC1R–MC5R) hit by α-MSH and synthetic analogs. MC1R → skin pigmentation; MC4R → libido + appetite. PT-141 and Melanotan-2 work here.
Microdosealso: microdosing: Using sub-therapeutic doses, often to reduce side effects while keeping some effect. Common with Retatrutide and Tirzepatide (start at 0.25 mg vs full 12-15 mg).
Mitochondriaalso: mitochondrial: The energy factories inside every cell. They turn food into ATP (cellular fuel). MOTS-c, NAD+, and SS-31 all target mitochondrial function.
Nootropic: A compound used to improve cognition — memory, focus, processing speed. Selank and Semax are peptide nootropics; coffee is the most-used non-peptide nootropic.
Pancreatitis: Inflammation of the pancreas. Sharp belly pain radiating to the back — medical emergency. Rare but real risk with GLP-1 drugs; stop immediately if suspected.
PK / PDalso: pharmacokinetics, pharmacodynamics: Pharmacokinetics (what the body does to the drug — absorption, distribution, metabolism, excretion) and pharmacodynamics (what the drug does to the body).
RCTalso: randomized controlled trial: Randomized Controlled Trial. The gold standard for evidence — participants randomly assigned to drug vs placebo, neither side knows which. "Phase 3 RCT" is the strongest signal a drug works.
Receptor: A protein on or in a cell that responds to a specific molecule. Peptide drugs work by binding receptors and changing cell behavior.
Reconstitutionalso: reconstitute: Adding sterile/bacteriostatic water to a lyophilized peptide vial to make it injectable.
Secretagogue: Any compound that causes your body to release something it already makes. "GH secretagogues" tell your pituitary to release growth hormone.
Subcutaneousalso: SubQ, SC, SQ, subcutaneous: Injection into fat just under the skin — usually belly, thigh, or upper arm. Most peptides are dosed this way; absorption is slower than IM.
Tachyphylaxis: Your body's response gets weaker with repeated doses. Some peptides (especially GH secretagogues) are cycled on/off to avoid it.
Titratealso: titration: Gradually step up a dose, usually to manage side effects. Standard practice for GLP-1s — start low, step up every 4 weeks.
TRTalso: testosterone replacement therapy: Testosterone Replacement Therapy. Prescription testosterone for men with low natural levels. Often discussed alongside peptides for stacking context.
VEGFalso: vascular endothelial growth factor: Vascular Endothelial Growth Factor. The main signaling molecule that drives new blood vessel growth. BPC-157 upregulates VEGF locally at injury sites.
α-MSHalso: alpha-MSH, alpha melanocyte stimulating hormone: Alpha-Melanocyte Stimulating Hormone. The natural hormone that activates melanocortin receptors — drives tanning and libido. PT-141 and Melanotan-2 are synthetic analogs.