The peptide glossary

A traditional compounding pharmacy, compounding for individually identified patients against a prescription.

A compounding facility registered with FDA that may produce larger batches without patient-specific prescriptions, and must follow GMP.

also: receptor agonist, agonists

A molecule that binds a receptor and activates it, producing the same kind of response as the body’s own signal.

also: amino acids, residue

The building block of peptides and proteins; twenty standard amino acids make up nearly all human biology.

also: primary structure, sequence

The exact order of amino acids in a peptide, which determines its identity and everything it does.

also: pramlintide, amylin analog

A hormone co-secreted with insulin that promotes satiety and slows gastric emptying; cagrilintide is a long-acting analog.

also: analogue, peptide analog, peptide analogue

A deliberately modified version of a natural peptide, altered to change its stability, potency, or duration.

also: anecdata, n=1, n of 1

A single person’s experience, offered as evidence — informative about that person, nearly silent about anyone else.

A non-human species used to study a disease or intervention before human testing.

also: receptor antagonist, blocker

A molecule that binds a receptor without activating it, blocking the body’s own signal from getting through.

also: active pharmaceutical ingredient

Active pharmaceutical ingredient — the raw drug substance, before it is formulated into a finished product.

Any analytical procedure that measures the presence, amount, or activity of a substance.

also: bac water, bacwater, bac-water

Sterile water containing about 0.9% benzyl alcohol as a preservative, allowing a vial to be entered more than once.

also: bud

The date after which a compounded or reconstituted preparation should no longer be used — distinct from a manufacturer’s expiry date.

The fraction of an administered dose that reaches systemic circulation intact.

A biological product highly similar to an approved reference biologic, with no clinically meaningful differences.

Two or more peptides pre-mixed in a single vial, as opposed to a stack of separately dosed compounds.

also: blood work, labs, panel

Blood tests, used to monitor markers before, during, and after using a compound.

also: broscience

Confident claims derived from gym-floor tradition and personal experience rather than controlled evidence.

also: coa, coas, cert of analysis

A laboratory report describing the identity, purity, and composition of one specific batch of material.

The plotted output of an HPLC run — the trace of peaks that a purity percentage is calculated from.

also: phase 1, phase 2, phase 3

The staged sequence of human testing: safety and dosing (I), preliminary efficacy (II), then large confirmatory trials (III).

also: cmax, tmax, peak concentration

Cmax is the peak concentration a dose reaches; Tmax is how long it takes to get there.

The unbroken sequence of temperature-controlled storage and transport that keeps a temperature-sensitive product intact.

also: compounding, compounded

A medicine prepared by a pharmacy to suit an individual patient — not FDA-approved, and not reviewed for safety or effectiveness before sale.

also: mg/ml, mcg/ml, strength

How much peptide sits in each millilitre of reconstituted solution — the number that converts a dose into a syringe volume.

A product deliberately misrepresented as a genuine one — wrong ingredient, wrong quantity, or no active ingredient at all.

also: cycling, on-cycle, off-cycle

A defined period of use followed by a deliberate break.

The U.S. National Library of Medicine’s repository of official, current FDA drug labelling.

also: dead volume, residual volume

The liquid left in the syringe hub and needle after the plunger is fully depressed.

Neither participants nor investigators know who received the drug, preventing expectation from shaping the results.

also: co-agonist, twincretin

A single molecule that activates two different receptors — for example tirzepatide at both the GIP and GLP-1 receptors.

also: lps, lal test, pyrogen

Bacterial cell-wall fragments that provoke fever and inflammation, detected by the LAL test — invisible to purity testing.

A grading of how much confidence the underlying research supports — from large human trials down to cell studies and anecdote.

A drug that FDA has reviewed and authorised for a specific use, having judged its benefits to outweigh its risks.

The persistent, intrusive mental chatter about food that many people report going quiet on GLP-1 drugs.

also: delayed gastric emptying, gastroparesis

The rate at which food leaves the stomach; GLP-1 drugs slow it, which drives both satiety and nausea.

also: ghrelin agonist, ghs-r agonist

A compound that mimics ghrelin, the hunger hormone, at its receptor — usually to trigger growth hormone release.

also: growth hormone releasing hormone, ghrh analog

Growth hormone-releasing hormone — the hypothalamic signal that tells the pituitary to release growth hormone.

also: growth hormone releasing peptide, ghrps

Growth hormone-releasing peptides — ghrelin-mimetic compounds that trigger growth hormone release through a different receptor than GHRH.

also: glucose-dependent insulinotropic polypeptide, gastric inhibitory polypeptide

The other major incretin hormone; tirzepatide targets its receptor alongside the GLP-1 receptor.

also: glucagon-like peptide-1, glp1, glp-1 receptor agonist

Glucagon-like peptide-1 — an incretin hormone that increases insulin secretion, slows gastric emptying, and reduces appetite.

The hormone that raises blood glucose — and, at the receptor level, a target for increasing energy expenditure.

also: good manufacturing practice, cgmp

Good Manufacturing Practice — the regulated system of processes and documentation required to make a medicine consistently.

also: gray market

The trade in products sold outside the regulated pharmaceutical channel, typically under a research-use-only label.

also: t1/2, elimination half-life

The time it takes for the concentration of a drug in the body to fall by half.

also: icp-ms, elemental impurities

Testing, usually by ICP-MS, for metallic contaminants at parts-per-billion levels.

also: high performance liquid chromatography, rp-hplc

High-performance liquid chromatography — the standard method for measuring how pure a peptide sample is.

also: insulin-like growth factor 1, igf1

Insulin-like growth factor 1 — the hormone, made largely by the liver in response to growth hormone, that mediates most of growth hormone’s effects.

Literally "in glass" — experiments on cells or tissues outside a living organism.

Experiments performed in a living organism, whether animal or human.

Analysis performed by the seller’s own laboratory rather than an independent one.

A gut hormone released after eating that amplifies insulin secretion — GLP-1 and GIP are the two main human incretins.

Systematically varying the injection location to avoid tissue damage and erratic absorption.

also: slin pin, slin-pin, u-100 syringe

A fine-gauge syringe graduated in insulin units rather than millilitres; the standard tool for small subcutaneous peptide doses.

also: im, i.m.

Injection into muscle tissue, producing faster absorption than subcutaneous injection but requiring a longer needle.

also: nasal spray

Delivery through the nasal mucosa, used for peptides such as selank, semax, oxytocin, and PT-141 in some formulations.

also: ind, investigational new drug

A compound under study in clinical trials but not yet approved for marketing.

Community shorthand for a boxed set of vials sold together, often ten at a stated strength.

The breakdown of stored triglycerides into fatty acids that can be used for energy.

also: front load, front-loading, frontloading

A larger initial dose intended to reach steady-state concentrations faster than regular dosing would.

also: batch number, batch, lot

The identifier for one specific production run, linking a physical vial to the certificate that describes it.

also: lyophilized, lyo, freeze-dried

Freeze-dried under vacuum — the state most research peptides ship in, because dry powder is far more stable than solution.

The steady dose taken once titration is complete and the intended effect has been reached.

also: ms, mass spec, lc-ms

A method that measures molecular mass, used to confirm that a sample is the peptide it claims to be.

also: moa, mechanism

The specific biochemical route by which a drug produces its effect — which receptor, which pathway, which tissue.

also: melanocortin receptor, mc4r, mc1r

A receptor family governing pigmentation, appetite, and sexual arousal — the target of PT-141 and melanotan II.

also: systematic review

A study that statistically pools the results of multiple prior studies to produce a combined estimate.

Taking a fraction of a standard dose, usually more frequently, in the hope of retaining benefit while reducing side effects.

also: mdv

A vial designed to be entered more than once, relying on a preservative to prevent microbial growth between uses.

also: national drug code

The National Drug Code — a unique identifier carried by every drug marketed in the United States.

also: peptide content, net content

The proportion of the vial’s total mass that is actually peptide, as opposed to water, salts, counter-ions, and bulking agents.

also: cognitive enhancer, smart drug

A substance claimed to improve cognition; among peptides, selank and semax are the most commonly discussed.

Prescribing an approved drug for an indication, dose, or population other than the one it was approved for.

also: ozempic butt, glp-1 face

Facial gauntness and sagging following rapid weight loss on a GLP-1 drug — caused by the weight loss, not by the drug itself.

A molecule that activates a receptor but cannot produce the full maximal response, even at saturating doses.

also: peptides

A short chain of amino acids joined by peptide bonds — larger than a single amino acid, smaller than a protein.

also: bioregulators, khavinson peptides

Very short peptides, often two to four amino acids, claimed to regulate gene expression in specific tissues.

also: pd

What the drug does to the body: the relationship between concentration and effect.

also: pk, adme

What the body does to the drug: absorption, distribution, metabolism, and excretion.

also: pin, pinned

Community slang for injecting.

An inert comparator that lets researchers separate a drug’s effect from the effect of being treated at all.

Research conducted before any human testing — in cells, tissues, or animals.

also: rx, rx-only, legend drug

A drug that may only be dispensed on the authorisation of a licensed prescriber.

A long amino-acid chain, conventionally more than about fifty residues, usually folded into a defined three-dimensional structure.

also: pmid, pmc, pubmed

The U.S. National Library of Medicine’s index of biomedical literature; a PMID is a study’s unique identifier within it.

also: gh pulse, pulsatility

The body releases growth hormone in bursts, mostly at night, rather than at a constant level.

also: area purity, hplc purity

The proportion of the detectable material in a sample that is the target peptide rather than peptide-related impurities.

also: rct, randomized controlled trial

A study in which participants are randomly assigned to treatment or control, isolating the drug’s effect from everything else.

A protein, usually on a cell surface, that a signalling molecule binds to in order to trigger a response inside the cell.

also: desensitisation, desensitization, tolerance

Cells reduce the number or sensitivity of receptors in response to persistent stimulation, blunting a drug’s effect over time.

also: recon, reconstitute, mixing

Dissolving a freeze-dried peptide powder into liquid — almost always bacteriostatic water — to make an injectable solution.

also: ruo, not for human consumption, research chemical

A label declaring a product is not intended for human use — which is what makes it saleable without approval.

also: reshipping, seizure

A vendor’s promise to resend an order that is seized in customs or lost in transit.

Traces of the organic solvents used during synthesis and purification that remain in the finished powder.

also: tfa salt, acetate salt, trifluoroacetate

The counter-ion paired with a peptide — commonly trifluoroacetate (TFA) or acetate — which contributes mass but no activity.

also: sarms, selective androgen receptor modulator

A selective androgen receptor modulator — a class that acts on the androgen receptor, and which MK-677 is routinely and wrongly lumped into.

also: growth hormone secretagogue, ghs

A substance that causes a gland to secrete a hormone the body already makes, rather than supplying the hormone directly.

also: sema, tirz, tirze

Community abbreviations for semaglutide, tirzepatide, retatrutide, and cagrilintide.

also: storage, stability

How long a peptide remains within specification under defined storage conditions.

also: source, sources

The practice — and the forum discussion — of finding a supplier for unapproved compounds.

also: stacking

Using two or more compounds together, typically chosen for complementary or additive mechanisms.

The point at which the amount of drug entering the body equals the amount leaving, so concentrations plateau.

also: swfi, sterile water

Preservative-free sterile water, intended for single use only.

The absence of viable microorganisms — a requirement for anything injected, tested separately from purity and identity.

also: subq, sub-q, sc

Injection into the fatty layer beneath the skin — the standard route for most peptide administration.

also: egg burps

Foul, sulphurous belching commonly reported on GLP-1 drugs, attributed to delayed gastric emptying.

also: biomarker endpoint

A measurable proxy — a blood marker, a scan — used to stand in for the outcome anyone actually cares about.

A rapid loss of response to a drug after repeated administration, occurring over hours or days rather than weeks.

also: independent testing, independent lab

Analysis performed by an independent laboratory with no commercial interest in the result.

also: titrate, titrate up, dose escalation

Increasing a dose gradually over weeks to let the body accommodate before reaching the target dose.

A single molecule activating three receptors — retatrutide targets GLP-1, GIP, and glucagon receptors.

also: underground lab, underground laboratory

Underground lab — an unlicensed operation producing or repackaging drugs outside any regulatory framework.

also: iu, insulin units, u-100

On a U-100 insulin syringe, 100 units = 1 mL. A unit is a volume, not a quantity of drug.

also: wada, banned substance, doping

The World Anti-Doping Agency’s annually updated list of substances prohibited in sport.

A drug-free interval long enough for a compound to clear the body before something else begins.

The community name for combining BPC-157 and TB-500, after the comic-book character’s regenerative healing.