Reference65 terms

Peptide glossary

This field borrows vocabulary from pharmacology, from regulation, and from forums — and then uses all three interchangeably. A "protocol" can mean a trial design or a screenshot. "FDA-approved" gets used as a badge rather than a statement about one specific indication. These are the definitions this site works from, including, where it matters, what a term is not.

A

Accelerated approval: A US regulatory pathway that lets a drug reach the market on a surrogate measure — a lab value or biomarker thought to predict benefit — rather than on proof of the outcome that matters to patients. It is a real approval, but a provisional one: confirmatory trials are still owed. A compound approved this way is not the same as one that met a hard clinical endpoint.
Adverse event: Any unwanted medical occurrence recorded during a trial, whether or not it was caused by the compound. Because the definition is deliberately wide, an adverse event count is not a side-effect count — separating the two is the job of the trial report, not the headline.
Agonist: A molecule that binds a receptor and switches it on, mimicking the body’s own signal. The opposite is an antagonist, which binds and blocks. Words like "dual agonist" or "triple agonist" simply mean the molecule activates two or three different receptors.
Amino acid: The individual building blocks that chain together to form peptides and proteins. There are twenty that the human body uses to build its own proteins. A single amino acid is not a peptide — you need at least two, joined by a peptide bond. The difference between the three is the most common point of confusion in the field.
Analog: A molecule deliberately modified from a natural one — an amino acid swapped, a chain shortened, a chemical group added — usually to change how long it lasts or how strongly it binds. An analog is a different molecule with different properties. Evidence collected on the original does not automatically transfer to it, which is one of the most frequently ignored distinctions in peptide marketing.
Approved abroad: Registered as a medicine by a regulator outside the US — commonly Russia, China, or the EU — but not by the FDA. It means real regulatory review happened somewhere, though standards, published trial data, and the approved formulation may all differ from what people actually buy.

B

Bacteriostatic water: Sterile water containing 0.9% benzyl alcohol, a preservative that inhibits bacterial growth inside a vial that will be punctured repeatedly. It is bacteriostatic, not bacteriocidal — it slows growth, it does not sterilise a contaminated vial. Full comparison in bacteriostatic vs. sterile water.
Bioavailability: The fraction of a dose that actually reaches the bloodstream intact. Route decides it: injected compounds are close to fully available, while most peptides swallowed as capsules are broken down by digestion before absorption. This is why an oral trial result rarely says anything useful about an injected form of the same compound.
Blend: Community usage: several peptides supplied premixed in one vial, sold under a coined name. What it means in practice is a fixed ratio chosen by a seller. No blend on the market has been trialled as a blend, so its evidence is at best the separate evidence of its parts — and combining components does not add evidence, it only adds variables.

C

Cardiolipin: A distinctive phospholipid found almost exclusively in the inner membrane of mitochondria, where it helps organise the machinery that produces cellular energy. Some compounds are described as "cardiolipin-targeting" because they concentrate at that membrane rather than acting on a conventional receptor.
Certificate of Analysis (COA): A lab document stating what a batch was tested for and what the test found — typically identity, purity by HPLC, and mass by spectrometry. A COA is only worth what the testing lab is worth: it should name a third-party lab, match the batch number on the vial, and be recent. A generic PDF with no batch number attached tells you nothing.
Compounded: Prepared by a compounding pharmacy for an individual, rather than manufactured and approved as a finished commercial product. Compounded versions of an approved drug are not themselves FDA-approved, and are not required to match the approved product’s formulation, testing, or labelling.
Concentration: How much compound sits in each unit of liquid, expressed as mg/mL. It is the single number that connects a mass you want to a volume a syringe can measure: peptide in the vial divided by water added. Nothing downstream works without it, which is why an unlabelled reconstituted vial is a dead end. Worked through in converting mg to mL.
Crossover trial: A trial design in which each participant receives both the compound and the comparator, in sequence, acting as their own control. It removes person-to-person variation and needs fewer participants, but is unsuitable when an effect might carry over into the next period.
Cycling: Community usage: running a compound for a set stretch, then deliberately stopping for a stretch before resuming. The stated rationale is usually avoiding receptor downregulation or tolerance. The on/off patterns circulated in forums are convention, not findings — very few of them correspond to any published schedule.

D

DAC / no-DAC: DAC stands for Drug Affinity Complex, a modification that binds a peptide to albumin in the blood so it clears over days rather than minutes. Two versions of the same base compound with and without DAC behave completely differently in the body — the difference is measured in orders of magnitude of duration, not in nuance. See CJC-1295 and ipamorelin.
Dead space: The small volume of liquid left in the needle hub and barrel after the plunger is fully depressed. On a fixed-needle insulin syringe it is negligible; on a detachable-needle syringe it can be a meaningful fraction of a small draw. It is a source of quiet loss, not a measurement error you can see.
Dose-ranging study: A trial run specifically to find out which doses do anything and which cause harm, usually early in development. Its absence is significant: when no dose-ranging study exists for a compound, every circulating figure is somebody’s convention rather than a finding.
Draw: Pulling solution from the vial into the syringe — and, by extension, the amount pulled. A single reconstituted vial is normally drawn from many times, which is what makes the choice of diluent and the vial’s stability window matter.

E

Evidence tier: This site’s four-level shorthand for how much human evidence stands behind a compound: approved (FDA-approved for at least one indication), human trials (substantial clinical data but not approved for the use discussed), early human data (small, old, single-group, or a different route than people use), and preclinical only (animal or mechanistic data plus convention). The tier describes the evidence, not the compound’s promise.

F

FDA-approved: Reviewed and authorised by the US Food and Drug Administration for one specific indication, in a specific formulation, at specific doses. Approval attaches to that indication only. "FDA-approved peptide" used as a general badge is close to meaningless — the question is always: approved for what?

G

Gauge: Needle thickness, on an inverted scale — a higher gauge number means a thinner needle. Insulin syringes commonly run 29G to 31G. Gauge affects comfort and how fast liquid moves; it has no bearing on the dose measured.
Ghrelin receptor: The receptor (formally GHS-R1a) that ghrelin, the so-called hunger hormone, acts on — and a second, separate route to growth hormone release alongside GHRH. Compounds acting here are often described as ghrelin mimetics or GH secretagogues.
GHRH: Growth hormone-releasing hormone: the natural signal from the hypothalamus that tells the pituitary to release growth hormone in pulses. Several research peptides are GHRH analogs, meaning they push the same lever rather than supplying growth hormone directly.
GIP: Glucose-dependent insulinotropic polypeptide, a gut hormone released after eating that works alongside GLP-1 on insulin release. It appears in the peptide world mainly because some newer metabolic drugs act on the GIP receptor as well as the GLP-1 receptor.
GLP-1: Glucagon-like peptide-1, a gut hormone that increases insulin release when blood glucose is high, slows stomach emptying, and reduces appetite. "A GLP-1" is now used loosely to mean any drug in the GLP-1 receptor agonist class — a shorthand that blurs together compounds with very different approval status and trial evidence. Background in GLP-1 and semaglutide.

H

Half-life: The time it takes for half the compound present to be cleared from the body. It shapes how long an effect can persist and how frequently a compound is administered in studies. Half-life describes clearance, not benefit — a long half-life says nothing about whether a compound works.

I

In vitro: Literally "in glass" — experiments on cells, tissue, or isolated molecules in a dish. In vitro work shows a mechanism is possible. It cannot show that anything happens in a living body, at reachable concentrations, without being cleared or broken down first.
In vivo: In a living organism. Unqualified, it almost always means animals — rodents, most often. In vivo evidence is a real step up from a dish, and still a long way short of a human result.
Insulin syringe: A small-volume syringe (commonly 0.3, 0.5, or 1 mL) with a fine fixed needle and a barrel marked in units rather than millilitres. It is the standard measuring instrument in this field because peptide volumes are far too small to read accurately on a conventional syringe.
Intramuscular (IM): Injection into muscle tissue, deeper than subcutaneous and generally with a longer needle. Absorption differs from the subcutaneous route, so doses and timings from an IM study do not transfer directly to a subcutaneous one.
Intranasal: Delivered as a spray or drops into the nose, absorbed across the nasal lining. This matters more than it sounds: several compounds whose clinical evidence comes entirely from an approved intranasal product are bought and injected instead, in which case the trial data describes a different route at a different dose.
Intravenous (IV): Delivered directly into a vein, usually by infusion under supervision. IV is the reference point for full bioavailability — and IV trial doses are the ones most often misquoted as if they applied to a subcutaneous syringe. They do not.
Investigational: Currently in clinical trials, not approved by any regulator. It signals that legitimate human research is under way and that the outcome is still unknown. An investigational compound sold outside a trial carries no approved formulation, dose, or label.

L

Loading dose: Community usage: a larger initial amount used at the start of a course, on the theory that it reaches a working level faster. The concept is genuine in clinical pharmacology, where loading doses are calculated from a drug’s known distribution and half-life. Applied to research peptides, the numbers are typically borrowed from forum convention with no such calculation behind them.
Lyophilised: Freeze-dried. The peptide is frozen and the water removed under vacuum, leaving a dry cake or powder that is stable far longer than a solution. The white puck at the bottom of a fresh vial is the lyophilised peptide, waiting to be reconstituted. Also spelled lyophilized.

M

Maintenance dose: Community usage: the steady ongoing amount that follows an initial or titration phase. In approved medicines this is a labelled figure derived from trials. For most research peptides there is no labelled maintenance dose — only a number that circulated widely enough to sound official.
mcg vs mg: Units of mass, a thousandfold apart: 1 mg = 1,000 mcg (micrograms). Some compounds are conventionally discussed in milligrams and others in micrograms, and a slipped decimal between them is the most consequential arithmetic error in this field. Convert everything into one unit before doing any other step.
Mitochondrial-derived peptide: A short peptide encoded within mitochondrial DNA rather than the cell’s nuclear genome — an unusual arrangement, and the reason this small family is studied separately. They are typically investigated for roles in metabolic and cellular stress signalling.

O

Off-label: Prescribing an approved drug for a condition, population, or dose other than the one on its label. Off-label use is legal and common in medicine, and it is not the same thing as unapproved: the drug itself has been reviewed, the specific use has not.
Open-label extension: A phase after the controlled portion of a trial in which everyone knows they are receiving the compound and there is no placebo group. Extensions are useful for spotting longer-term safety signals, and weak as efficacy evidence, because expectation and the absence of a control both push results in the same direction.

P

Pentadecapeptide: A peptide fifteen amino acids long. Nothing more is implied — the prefix is a count, not a category or a quality claim. It shows up frequently because one widely discussed recovery compound is described that way in the literature.
Peptide: A short chain of amino acids joined by peptide bonds, generally under about fifty. Peptides are how the body signals to itself — hormones, growth factors, and messengers are largely peptides. The word describes a molecular size class, not a drug category and not a benefit. Start with what peptides are.
Phase 1 / 2 / 3: The three stages of human drug testing. Phase 1 asks whether a compound is tolerated, usually in a small group of healthy volunteers. Phase 2 looks for a signal of effect and a workable dose in patients. Phase 3 is the large randomised test that approval decisions rest on. A compound "in trials" at Phase 1 and one at Phase 3 are separated by years and by most of the evidence.
Placebo-controlled: A trial in which a comparison group receives an inactive substitute, so that the measured effect can be separated from expectation and from natural improvement over time. Without a control group, an uncontrolled improvement is just an observation.
Preclinical: Everything before human testing: cell work, animal studies, mechanistic modelling. Preclinical results describe what might happen. Many compounds with impressive preclinical files have failed in humans, so a strong rodent literature is a reason to keep studying something — not evidence that it works.
Primary endpoint: The single outcome a trial is designed and statistically powered to answer, declared before the trial starts. When a trial misses its primary endpoint but reports positive secondary findings, those findings are hypothesis-generating — the trial did not demonstrate what it set out to demonstrate.
Protein: A long amino acid chain — roughly fifty residues and up — folded into a specific three-dimensional shape. The boundary with "peptide" is a convention of length rather than a hard chemical line, but the practical difference is real: proteins fold, and the fold is usually what does the work.
Protocol: In research, the written plan governing a study: who, what dose, how often, what is measured. In community usage, the word has drifted to mean any circulating dose-and-schedule recipe. Those two meanings are not equivalent, and a "protocol" passed between forums has none of the design, oversight, or measurement the word implies.

R

Randomised controlled trial (RCT): A study in which participants are assigned by chance to the compound or a control, so that the groups differ only in what they received. Randomisation is what makes causal claims possible. It is also the design most conspicuously missing behind most peptide claims.
Receptor: A protein, usually on a cell surface, that a signalling molecule binds to in order to trigger a response inside the cell. Which receptors a compound binds — and how tightly — determines what it does. Broadly explained in how peptides work in the body.
Reconstitution: Adding a sterile diluent to a lyophilised vial to dissolve the powder into a measurable solution. The volume chosen is not fixed by the vial — it sets the concentration, and therefore how easy the resulting numbers are to measure. Our reconstitution calculator runs the arithmetic, and how much water to add covers the choice itself.
Research use only: A supply-side label meaning the material is sold for laboratory work and is not approved, tested, or intended for human use. It is not a legal status: Health Canada stated in April 2026 that the label confers none, and it says nothing about purity or safety either. The beginner’s guide covers what the label does and does not tell you.

S

Secretagogue: A compound that causes the body to secrete more of something it already makes. A growth hormone secretagogue prompts the pituitary to release its own growth hormone rather than supplying growth hormone from outside — a genuinely different mechanism, and often blurred in marketing copy.
Sequence: The specific order of amino acids in a peptide, the thing that defines its identity. A sequence written on a vial label or a COA is checkable; a coined product name is not. Two products with the same trade name and different sequences are different compounds.
Stack: Community usage: two or more compounds used together, either premixed or administered separately. Stacks are almost never studied as stacks, so their evidence is the sum of the parts at best — and interactions, whether helpful or harmful, are exactly what has not been tested. A worked example is the so-called Wolverine stack.
Sterile water for injection: Water that has been sterilised, with nothing added. It dissolves a lyophilised peptide just as well as bacteriostatic water, but contains no preservative — so once the seal is punctured, standard practice treats the vial as single-use.
Subcutaneous (SC/SubQ): Injection into the fat layer just under the skin, the route most research peptides are administered by. Absorption is slower and steadier than intravenous. It is also, notably, the route that most peptide trial data was not collected on.

T

Telomerase: The enzyme that rebuilds telomeres, the protective caps at the ends of chromosomes that shorten as cells divide. It is a recurring theme in longevity research because telomere shortening is a marker of cellular ageing — though a marker moving is not the same as ageing changing. Context in the telomere peptide article.
Tetrapeptide: A peptide four amino acids long. Like other length prefixes — dipeptide, tripeptide, pentadecapeptide — it counts residues and implies nothing else.
Titration: Stepping an amount up gradually rather than starting at the target, usually to let tolerability catch up. For approved drugs the titration schedule is on the label and came from trials. Elsewhere the word is often borrowed to dress up a self-designed ramp.

U

U-100: The concentration standard almost all insulin syringes are calibrated to: 100 units per millilitre. It is why 1 unit equals 0.01 mL, and why multiplying millilitres by 100 gives units. U-40 syringes exist on a different scale, so the barrel is worth checking before trusting the arithmetic.
Unit: A mark on an insulin syringe barrel measuring volume, not compound: on a U-100 syringe, 1 unit is 0.01 mL. "Ten units" therefore means nothing on its own — the amount of peptide it contains depends entirely on the concentration in the vial. Explained in what units mean on an insulin syringe.

V

Vial: The small sealed glass container a peptide is supplied in, closed with a rubber septum that a needle passes through without opening it. Labelled vial contents are stated as mass (e.g. 5 mg), which is why concentration only exists once a diluent has been added and recorded.

W

Withdrawn: Formerly approved, then removed from the market. Withdrawal is not automatically a safety verdict — products are also discontinued commercially — so the reason matters, and it is usually documented.

Definitions describe how terms are used, not what any compound does. Nothing here is a dose, a protocol, or medical advice — see the editorial policy, and if a definition is wrong, say so.