Glossary

95 terms in plain language — the peptide chemistry, pharmacokinetics and research words the rest of the site uses, each linked to the pages where it comes up.

Peptide chemistry

Acylationalso: fatty-acid acylation, acylated: Attaching a fatty-acid tail to a peptide so it sticks to albumin, a carrier protein in the blood. The peptide is then released slowly, which stretches a same-day compound out to once-weekly.
Aggregation: When peptide molecules clump together in solution instead of staying separate. Clumped peptide is no longer the intact single molecule, so aggregation quietly lowers how much usable compound a mixed vial holds.
Amino acid: The building blocks a peptide is made of. Twenty common ones spell out every natural peptide, and the order they appear in is what makes one peptide different from another.
Amino acid sequencealso: sequence, primary structure: The exact order of amino acids in a peptide, written as a string of letters. It is the peptide's identity — change one letter and it is a different molecule, which is what a mass-spectrometry check confirms.
Analogalso: analogue: A close copy of a natural peptide with a deliberate change or two, made to last longer or act more strongly than the original. Most of the metabolic compounds here are analogs of gut hormones.
C-terminal amidationalso: amidation, amidate, amide: A small tweak that caps one end of the chain with an amide group. It makes many peptides last longer and work better, which is why some names carry an -amide tag.
DAC (Drug Affinity Complex)also: dac, drug affinity complex: A group added to a peptide so it latches onto albumin in the blood and lasts for days instead of minutes. The DAC and no-DAC versions of a compound are different molecules with very different half-lives.
Fc fusionalso: fusion protein, fc-fusion: Fusing a peptide to the Fc piece of an antibody so it borrows the antibody's long life in the blood. It is what lets some GLP-1 compounds be given only once a week.
Fragment: A piece cut out of a larger protein rather than the whole thing. A fragment can keep part of the parent's activity while being much smaller and cheaper to make.
Lyophilizationalso: freeze-drying, lyophilisation, lyophilized, freeze dried: Freeze-drying: pulling almost all the water out of a frozen peptide under vacuum to leave a dry powder. Dry and cold is the most stable a peptide gets, which is why vials arrive as powder to be mixed later.
Molecular weightalso: molecular mass, molar mass, mw: How much one molecule weighs, set by its sequence. Because the number is fixed and predictable, a mass check is a strong way to confirm a vial holds the molecule the label names.
N-terminus and C-terminusalso: n-terminus, c-terminus, termini: The two ends of a peptide chain, named after the chemical group that sits there. Both ends are common places to make a small change that slows how fast the body breaks the chain down.
PEGylationalso: pegylated, peg: Bolting a chain of polyethylene glycol (PEG) onto a peptide to make it bigger and slower to clear. It is another way to turn a short-acting molecule into a long-acting one.
Peptide: A short chain of amino acids joined in a line, like a very small protein. Most compounds on this site are peptides; a few are small molecules or larger proteins grouped alongside them.
Peptide bond: The chemical link that holds one amino acid to the next along the chain. Breaking these bonds is what taking a peptide apart means, and it is why peptides do not survive the stomach well.
Peptide degradationalso: degradation, breakdown, oxidation, deamidation: The slow chemical breakdown of a peptide — chains clipping, unfolding or reacting with oxygen and water. It runs faster when a vial is warm, wet or in the light, and it cannot be reversed once it has happened.
Salt formalso: acetate salt, tfa, trifluoroacetate, acetate: The chemical pairing a dry peptide ships as, usually acetate or trifluoroacetate (TFA). The salt adds weight that is not peptide, so a vial can weigh what the label says while holding a little less actual compound.

Pharmacokinetics

Accumulation ratioalso: accumulation: How much higher the steady level is than a single dose's peak. The closer the gap between doses is to the half-life, the more a compound stacks up.
Agonist: A compound that switches a receptor on, copying the body's own signal. Most metabolic and growth peptides here are agonists of a natural hormone's receptor.
Antagonist: A compound that blocks a receptor so the normal signal cannot act, the opposite of an agonist.
Area under the curvealso: auc: The total exposure from a dose, found by adding up the blood level across all the hours it is present (the area under the level-versus-time curve). It captures the whole dose, not just the peak.
Bioavailability: The share of a dose that actually reaches the bloodstream intact. A shot under the skin is close to fully available; the same peptide swallowed is often near zero, because the gut breaks it apart.
Clearance: How quickly the body removes a compound, mostly through the liver and kidneys. Faster clearance means a shorter half-life and more frequent dosing.
Downregulation: When a cell cuts back the number of receptors on its surface after being signalled at non-stop. It is why a steady, constant push can produce less effect over time.
Efficacy: The size of the largest effect a compound can produce, no matter how much is given. High potency and high efficacy are separate things.
First-pass metabolismalso: first pass: The chunk of a swallowed dose destroyed by the gut and liver before it ever reaches general circulation. It is a big reason most peptides are injected rather than taken by mouth.
Half-lifealso: elimination half-life, t1/2, half life: The time it takes for the amount in the body to fall by half. After three half-lives about an eighth is left; it is the single number that most shapes how often a compound is given.
Peak concentrationalso: cmax, c max, tmax, time to peak: The highest level a dose reaches in the blood (Cmax), and how long it takes to get there (Tmax). A slow route under the skin gives a lower, gentler peak than the same amount straight into a vein.
Pharmacodynamicsalso: pd: What the compound does to the body — the link between how much is present and the size of the effect. It is the other half of the pair with pharmacokinetics, which tracks the amount over time.
Pharmacokineticsalso: pk: What the body does to a compound: how it is absorbed, spread around, broken down and cleared out. It is the maths behind how long a dose lasts and how often one is given.
Potency: How little of a compound it takes to get an effect. A more potent compound reaches the same result at a smaller amount — it says nothing about how large the top effect can be.
Protein bindingalso: albumin binding, plasma protein binding: How tightly a compound sticks to carrier proteins such as albumin in the blood. Strong, deliberate binding is a common trick to make a peptide last for days.
Receptor: A protein switch on or inside a cell that a signal fits into like a key in a lock. A peptide works by binding its receptor; which receptor it fits decides what it does.
Steady state: The level a compound settles at once the amount cleared between doses matches the amount added. It is reached after roughly five half-lives of regular dosing.
Titrationalso: dose escalation, escalation: Stepping an amount up (or down) gradually rather than starting at the full figure. The GLP-1 compounds are titrated over weeks to let the body settle and to limit stomach upset.
Tolerance: The same amount producing a smaller effect the longer it is used, often because of downregulation. A break is what lets receptors recover and tolerance fade.

Compound classes

Amylin analogalso: amylin, amylin analogue: A copy of amylin, a hormone released with insulin that curbs appetite and slows the stomach. These are studied alongside or blended with GLP-1 compounds.
Body protective compoundalso: bpc, bpc-157, body protection compound: A short peptide drawn from a protein found in the stomach, studied in animals for tissue repair. BPC-157 is the well-known member; its human evidence is thin.
Copper peptidealso: ghk-cu, copper tripeptide: A peptide that carries a copper atom, best known as GHK-Cu. Most of its solid evidence is for skin applied on the surface rather than for injection.
Dual and triple agonistalso: co-agonist, dual agonist, triple agonist, multi-agonist: One molecule built to switch on two or three hormone receptors at once — for example GLP-1 plus GIP, or those two plus glucagon. Combining signals is the idea behind the newest weight compounds.
Ghrelin mimeticalso: ghrp, growth hormone releasing peptide, ghrelin: A compound that copies ghrelin, the hunger hormone, to trigger a pulse of growth hormone. These pair up with GHRH analogs, which push the same system through a different door.
GHRH analogalso: ghrh, growth hormone releasing hormone: A copy of the natural signal (GHRH) that tells the pituitary gland to make growth hormone. Sermorelin, tesamorelin and CJC-1295 are members of this class.
GIP receptor agonistalso: gip, glucose-dependent insulinotropic polypeptide: A compound acting on the receptor for GIP, a second gut hormone that works with GLP-1. Tirzepatide hits both GIP and GLP-1 at once.
GLP-1 receptor agonistalso: glp-1, glp1, glucagon-like peptide-1: A compound that copies the gut hormone GLP-1, which nudges insulin up after a meal and slows the stomach. This class is studied heavily for blood-sugar control and weight, and includes semaglutide and liraglutide.
GnRH agonistalso: gnrh, gonadotropin-releasing hormone, gonadorelin: A copy of the brain signal (GnRH) that tells the body to make sex hormones. A steady dose and a pulsed dose of this class can have opposite results, which is a key quirk of it.
Growth hormone secretagoguealso: ghs, gh secretagogue, secretagogue: A compound that prods the body to release its own growth hormone in pulses, rather than adding growth hormone from outside. It is an indirect nudge that works with the body's own on-off control.
IGF-1also: igf-1, insulin-like growth factor 1, igf1: Insulin-like growth factor 1, the hormone that carries out many of growth hormone's downstream effects in tissue. Modified versions such as IGF-1 LR3 are made to last longer than the natural one.
Incretin: The family name for gut hormones — GLP-1 and GIP — that tell the body to release insulin after eating. The metabolic peptides here mostly copy or combine these signals.
Kisspeptin: A peptide that sits at the top of the chain controlling the body's sex hormones, kicking off the release of the hormones that drive reproduction. Human studies of it use short infusions into a vein.
Melanocortin receptor agonistalso: melanocortin, mc4r, mc1r: A compound acting on melanocortin receptors, which sit behind skin pigment, appetite and sexual arousal depending on the receptor. The class includes the tanning and libido peptides.
Mitochondrial-derived peptidealso: mitochondrial peptide, mdp: A small peptide encoded inside the mitochondria, the cell's power plants, rather than the main genome. MOTS-c and humanin are the examples catalogued here, studied for metabolism and ageing.
Nootropic peptidealso: nootropic, cognitive peptide: A peptide studied for effects on focus, mood or memory, most of them acting in the brain. Semax and Selank are the best-known examples here.
Peptide blendalso: blend, stack, fixed-ratio blend: Several peptides sold in one vial at a fixed ratio, drawn together as a whole. A blend has no single half-life because its parts clear at different speeds, so each one is charted separately.
Thymic peptidealso: thymic, thymosin: A peptide first found in the thymus, a gland that trains immune cells. This group is studied for its effects on immune signalling.

Research methods

Certificate of analysisalso: coa, cofa, certificate of analysis: The lab document that says what is in a vial — its identity, its purity and often its water content. It is the main evidence a buyer has that the powder matches the label.
Clinical trial phasesalso: phase 1, phase 2, phase 3, phase i, phase ii, phase iii: The steps a compound moves through in people: phase 1 checks safety in a few volunteers, phase 2 looks for an effect and a workable amount, and phase 3 tests it in a large group.
Dose-ranging studyalso: dose-finding, dose ranging: A study that compares several amounts to find the one with the best balance of effect and side effects. This site only shows a schedule table where a human dose-ranging study backs it.
Double-blindalso: double blind, blinding: A study set up so neither the volunteers nor the staff know who is getting the real compound and who is getting the placebo. It stops expectations on either side from bending the result.
Evidence tieralso: tier, evidence grade: This site's A-to-D grade for how much dosing evidence stands behind a compound: A is a real human trial at the route used, D is little or no human data. It is shown so a reader knows how solid a figure is.
HPLCalso: high-performance liquid chromatography, high performance liquid chromatography: High-performance liquid chromatography, the test that answers “how much of this is the right molecule?” It reports purity as the main peak's share of everything the detector saw.
In vitro: Latin for “in glass”: an experiment run in a dish or test tube, on cells or isolated molecules. It is fast and cheap but a long way from how a whole body behaves.
In vivo: An experiment run in a living body, usually an animal before it is a person. In-vivo results carry more weight than in-vitro ones but still may not transfer between species.
Lot numberalso: batch number, lot, batch: The code marking one specific production run. A certificate of analysis only describes the lot it names, so its number should match the vial in hand.
Mass spectrometryalso: mass spec, ms: A test that weighs the molecule to answer “is this the right compound?” Because a peptide's weight is fixed by its sequence, a matching mass is strong proof of identity.
Peptide contentalso: net peptide content, water content: The share of a vial's weight that is actual peptide, after water and salt are set aside. It is a different number from purity, and a vial can be very pure yet hold less peptide than its milligram label suggests.
Placebo: A dummy with no active ingredient, given to some volunteers in a study so a real effect can be told apart from expectation and the natural ups and downs of a condition.
Preclinicalalso: pre-clinical: Research done before any human study — in cells or in animals. Many compounds here rest on preclinical work only, which is a weak basis for guessing what happens in a person.
Purity: The share of the peptide in a vial that is the right peptide, usually read off an HPLC chart. It says nothing about how much peptide the vial holds by weight — that is peptide content.
Randomized controlled trialalso: rct, randomised controlled trial, randomized: A study that splits volunteers at random into a group getting the compound and a group getting a dummy, then compares them. It is the strongest ordinary way to tell a real effect from chance.
Third-party testingalso: third party testing, independent testing: Sending a vial to an outside lab, rather than trusting the seller's own sheet, and publishing what comes back. It is the usual answer to the obvious conflict of interest in a seller-supplied certificate.

Supplies & measurement

Bacteriostatic wateralso: bac water, bacteriostatic: Sterile water with a small amount of benzyl alcohol added as a preservative, so one vial can be entered many times over weeks. It is what most freeze-dried peptides are mixed with.
Cold chainalso: cold-chain, cold shipping: Keeping a compound cold every step from maker to fridge, since every warm hour subtracts a little from what is left and never comes back. A cold pack that arrives still cold is the easy check.
Concentration: How much compound sits in each millilitre of a mixed vial — the vial's amount divided by the water added. It decides how many syringe units a given dose lands on.
Cost per dosealso: cost per draw, price per dose: What a single draw works out to once a vial's price is spread across the doses it holds — including any that stay stuck in a part-used vial. It is the honest way to compare vial sizes.
Injection penalso: cartridge pen, pen: A reusable device that dials a dose in fixed clicks instead of being read off a barrel. A dose that falls between two clicks has to round to one of them, which the calculators account for.
Intramuscularalso: im, intra-muscular: Into a muscle, abbreviated IM, using a longer needle than a subcutaneous shot. The route changes how fast a compound is absorbed, so a figure measured one way does not carry to the other.
Intranasalalso: nasal, intra-nasal: Through the nose, as a spray or drops. Some peptides, such as Semax and Selank, are used this way where they are sold.
Intravenousalso: iv, intra-venous: Straight into a vein, abbreviated IV. It puts the whole dose into the blood at once, giving a sharp peak — several compounds here were only ever studied in people this way.
Milligram and microgramalso: mg, mcg, microgram, milligram, µg: Units of weight one thousand apart: one milligram (mg) is a thousand micrograms (mcg). Mixing the two up is a thousandfold error, so this site keeps vial sizes in mg and doses in mcg where that reads clearer.
Reconstitutionalso: reconstitute, mixing: Adding liquid to a freeze-dried powder to turn it back into a solution that can be drawn up. How much liquid you add is a free choice that sets the concentration.
Sterile wateralso: sterile water for injection: Plain water with no preservative, meant for a single use. Because nothing holds microbes in check, a vial mixed with it is not meant to be kept and re-entered like one mixed with bacteriostatic water.
Subcutaneousalso: subq, sc, sub-q, under the skin: The fat layer between skin and muscle, abbreviated sc or subQ. Most research peptides are described going here, where a short needle reaches and the compound is absorbed gradually.
U-100 syringealso: u100, u-100, insulin syringe: The standard insulin syringe, marked for a liquid holding 100 units per millilitre. On it one unit is 0.01 mL, so a full 1 mL syringe reads 100 units.
Unitalso: insulin unit, iu: A mark on an insulin syringe measuring volume, not amount of compound. Ten units is 0.1 mL whatever is dissolved in it — how much compound that holds depends entirely on the concentration.

Regulatory & legal

Compounding pharmacyalso: compounding, compounded: A pharmacy that makes a medicine to order — mixing or adjusting ingredients for one person — instead of selling a mass-produced pack. Some peptides reach people through this route where it is allowed.
Controlled substancealso: scheduled substance, controlled drug: A compound a government restricts by law because of misuse risk, with penalties for handling it outside the rules. Most peptides here are not scheduled, but the category matters for anything that is.
GMPalso: good manufacturing practice, gmp-grade: Good Manufacturing Practice: a formal standard for how a compound is made, tracked and tested. A vial made to GMP has documentation behind it that a plain research-chemical vial usually does not.
GRASalso: generally recognized as safe, generally recognised as safe: “Generally Recognized as Safe,” a US label for a food ingredient with a long safe track record. It is a food-law status, not a sign a compound has been reviewed as a medicine.
Grey marketalso: gray market, grey-market: The trade in compounds that are legal to sell as research chemicals but not cleared for the human use buyers often have in mind. It is where most peptides here are actually bought.
Investigational New Drugalso: ind, investigational: In the US, the filing that lets a not-yet-licensed compound be given to people in a study. A compound at the IND stage is being tested, not cleared for sale.
Licensed medicinealso: licensed drug, approved medicine: A compound a regulator has cleared for sale as a medicine in a given country, after reviewing its evidence. A minority of entries here are licensed somewhere; each such entry says where.
Not for human usealso: nfhu, research use only, ruo: The label a research chemical carries, marking it as sold for lab study rather than for a person. It sets the terms the whole grey market runs on.
Off-labelalso: off label: Using a licensed medicine for a purpose, group or amount it was not licensed for. It is legal and common in ordinary medicine, and it is different from using an unlicensed compound.
Research chemicalalso: research chemicals, rc: A compound sold for laboratory work and labelled not for human use. Most entries on this site fall here — the label is a legal line, and it is why nothing on the site is a recommendation to use anything.
USP gradealso: usp, united states pharmacopeia: A quality standard set by the US Pharmacopeia for the purity and testing of an ingredient. Bacteriostatic water sold as USP grade has met that published bar.