Peptide Terminology Glossary (A–Z)
Every term you will hit reading a peptide guide, a product label, a certificate of analysis or a research paper — defined in plain language, without assuming you already know the neighbouring term.
Around 120 terms covering chemistry, pharmacology, administration, product quality, regulation and research methodology. Definitions are written for a general reader. This is educational content only and not medical advice.
Peptide writing has an unusually steep vocabulary problem. A single product page can throw lyophilized, secretagogue, subcutaneous, COA and RUO at you in one paragraph, and most glossaries define each term using three others you also do not know.
This one tries not to do that. Where a definition depends on another term, it explains the dependency rather than pointing at it. If you are starting from zero, our guides on how peptides work in the body and the different types of peptides are the two worth reading first.
503A
The section of US law covering traditional compounding pharmacies, which prepare medicines for individual patients against a prescription. The "503A bulks list" names the raw substances such pharmacies may legally compound with — which is why peptide regulation discussions keep returning to it.
503B
The section covering outsourcing facilities, which compound in larger batches without patient-specific prescriptions and operate under stricter manufacturing standards than 503A pharmacies.
U-100
The calibration standard for insulin syringes, where 100 units equals exactly 1 millilitre. Almost all peptide dosing guidance assumes this scale. See also units.
Acetate salt
A common form in which peptides are supplied, where the peptide is paired with acetate ions to make it stable and easier to handle. Because the salt adds weight, a vial labelled by salt weight contains slightly less actual peptide than one labelled by free-base weight.
Affinity
How tightly a molecule binds to its receptor. High affinity means it attaches readily and stays bound; low affinity means it detaches quickly. Affinity is about binding strength, not about how large an effect follows.
Agonist
A molecule that binds a receptor and switches it on, producing the same kind of response the body's own signalling molecule would. Most therapeutic peptides are agonists of something.
Amidation
A chemical modification to the tail end of a peptide chain that makes it harder for enzymes to chew through, extending how long it survives in the body.
Amino acid
The building block of every peptide and protein. Twenty standard amino acids are used by human biology, each with a different side group giving it distinct chemical behaviour. String them together and their order determines what the resulting molecule does.
AMPK
AMP-activated protein kinaseAn enzyme acting as the cell's fuel gauge. When it activates, the cell shifts from storing energy to burning it — more glucose uptake, more fat oxidation. Several metabolic compounds are discussed in terms of AMPK activation.
Analog
also analogueA molecule deliberately modified from a natural one, usually to make it last longer, bind more selectively, or resist breakdown. Semaglutide is an analog of GLP-1: recognisably related, but engineered.
Angiogenesis
The growth of new blood vessels. Relevant to healing research because tissue repair depends on blood supply — and relevant to caution, because the same process feeds tumours.
Antagonist
The opposite of an agonist: a molecule that occupies a receptor and blocks it, preventing the normal signal from getting through.
AUC
area under the curveA measure of total drug exposure over time, combining how high the concentration got with how long it stayed up. Two compounds can reach the same peak but deliver very different AUCs.
Bacteriostatic water
BAC waterSterile water containing 0.9% benzyl alcohol as a preservative. The preservative is what makes it reasonable to draw from the same vial repeatedly over days, rather than once. See our reconstitution guide.
Batch
also lotA single production run of a product. Testing applies to a batch, not to a brand — which is why a certificate of analysis is only meaningful if its batch number matches the vial in your hand.
BDNF
brain-derived neurotrophic factorA growth factor supporting the survival of neurons and the formation of new connections between them. Frequently cited in cognitive peptide research. Exercise raises it reliably.
Benzyl alcohol
The preservative in bacteriostatic water, present at 0.9%. It suppresses bacterial growth and has a mild numbing effect. It is also why bacteriostatic water is unsuitable for newborns.
Bioavailability
The proportion of a dose that actually reaches your bloodstream in working condition. Injected peptides score high; swallowed ones usually score very low, because digestion destroys them before absorption.
Bioregulator
A loose category covering very short peptides — often two to four amino acids — from a mainly Russian research tradition, proposed to act on gene expression rather than by binding receptors. The proposed mechanism is not well established outside that literature.
Blood-brain barrier
The selective filter separating the bloodstream from brain tissue. Most large molecules cannot cross it, so a compound intended to act on the brain has to be small enough, or use a transport route, or be delivered another way.
Bolus
A single dose delivered all at once, as opposed to a continuous infusion.
Certificate of Analysis
COAA laboratory document reporting what testing found in a specific batch — typically identity and purity, sometimes endotoxin. A certificate without a batch number, a named lab and a date proves very little. See understanding purity and COAs.
cGMP
current Good Manufacturing PracticeThe regulated manufacturing standard applied to medicines, covering facilities, documentation, testing and traceability. Research compounds are not made under it, which is the core practical difference between research and pharmaceutical grade.
Chirality
The property of a molecule existing in two mirror-image forms. Biology overwhelmingly uses one form of amino acids; swapping in the mirror version at a specific position is a common trick for making a peptide resist enzymes.
Cmax
The highest concentration a compound reaches in the blood after a dose. Paired with Tmax, the time at which that peak occurs.
Cold chain
Keeping a temperature-sensitive product refrigerated continuously from manufacture to use. A break anywhere in that chain can degrade a peptide invisibly — the powder looks identical either way.
Compounding pharmacy
A licensed pharmacy that prepares customised medicines for individual patients rather than dispensing pre-manufactured products. Which substances may be compounded is tightly controlled, and most research peptides are not on the permitted list.
Concentration
How much peptide sits in each millilitre of solution, expressed as mg/ml. It is set entirely by how much water you added: the same vial can produce any concentration you like. Our reconstitution calculator does the arithmetic.
Confounder
Something that changed alongside the thing you are studying and could explain your result instead. Starting a compound the same month you fixed your sleep means sleep is a confounder.
Crossover trial
A study design where each participant receives both the treatment and the placebo in sequence, so they act as their own comparison. Efficient with small groups, which is why several early peptide studies used it.
Cycling
Running a compound for a set period, then taking a break before resuming. Widely practised. For most research peptides the specific schedules come from convention rather than from studies of tolerance.
Cyclic peptide
A peptide whose two ends are joined into a ring. Having no loose ends makes it far harder for enzymes to break down, so cyclic peptides tend to last considerably longer than linear ones.
Dalton
DaThe unit used for molecular weight. A typical short peptide runs from a few hundred to a few thousand daltons. A thousand daltons is a kilodalton (kDa).
Dead space
The small volume of liquid left inside a syringe and needle after the plunger is fully depressed. It is why a vial rarely yields quite as many doses as the arithmetic suggests.
Desensitisation
A receptor becoming less responsive after sustained stimulation. It is the biological reason behind cycling, and it varies enormously between compounds.
Dipeptide
Two amino acids joined together. Tripeptide is three, tetrapeptide four, and so on. Glutathione, the body's main antioxidant, is a tripeptide.
Disulfide bond
A chemical bridge between two sulphur-containing amino acids that pins a peptide into a particular shape. Peptides with disulfide bonds are generally sturdier; those without are more fragile in handling.
Dose-response curve
A plot of how the effect changes as the dose rises. Often it climbs then plateaus. Sometimes it is bell-shaped, meaning the effect peaks at a middle dose and gets smaller at higher ones — which is the opposite of most people's intuition.
Double-blind
A study in which neither the participants nor the researchers assessing them know who received the real treatment. This is what stops expectation from contaminating the result, and its absence is the main weakness of most peptide research.
DPP-4
dipeptidyl peptidase-4An enzyme that rapidly clips apart certain peptides, including natural GLP-1 — which is why the natural hormone lasts about two minutes. Engineering a molecule to resist DPP-4 is what turns a two-minute peptide into a weekly injection.
Dual agonist
A single molecule that activates two different receptors. Tirzepatide is the well-known example, acting on both GLP-1 and GIP receptors. A triple agonist activates three.
EC50
The concentration producing half of a compound's maximum possible effect. It is a potency measure: a lower EC50 means less is needed. Potency is not the same as effectiveness — a very potent compound can still do something unhelpful.
Effect size
How large a difference a treatment made, as distinct from whether the difference was statistically detectable. A result can be highly significant and still too small to notice.
Endogenous
Produced inside your own body. Insulin, oxytocin and GLP-1 are all endogenous peptides. The opposite is exogenous — administered from outside.
Endotoxin
Fragments of bacterial cell wall that survive sterilisation and cause fever and inflammation when injected. Critically, a purity test does not detect them — endotoxin needs its own assay, which many certificates omit.
Excipient
An inactive ingredient added alongside the active compound — bulking agents, stabilisers, pH adjusters. Mannitol is a common one in lyophilized peptide vials.
Exogenous
Coming from outside the body. An injected peptide is exogenous, even when the molecule is chemically identical to one you produce yourself.
FDA
US Food and Drug AdministrationThe American regulator responsible for approving medicines. Its decisions shape the peptide market well beyond the United States, because supply chains and compounding rules follow them.
First-pass metabolism
The processing a swallowed substance undergoes in the gut wall and liver before reaching general circulation. It is one reason oral versions of injectable compounds deliver so much less.
Fragment
A section cut out of a longer peptide or protein and used on its own. BPC-157 is a fifteen-residue fragment of a larger gastric protein. A fragment does not necessarily behave like the whole molecule.
Free base
The peptide weighed without any accompanying salt. Labels quoted as free base indicate slightly more active material than the same number quoted as salt weight — worth asking about when precision matters.
Gauge
GNeedle thickness, counted backwards: a higher gauge number means a thinner needle. Insulin syringes typically use very fine needles, which is a large part of why the injection is less unpleasant than people expect.
GHK-Cu
A naturally occurring three-amino-acid peptide bound to a copper ion, studied for skin and wound applications. Commonly called a copper peptide.
GHRH
growth hormone-releasing hormoneThe hypothalamic signal telling the pituitary to release growth hormone. Sermorelin, CJC-1295 and tesamorelin are all built on this pathway. See how growth hormone peptides work.
GHRP
growth hormone-releasing peptideA separate class prompting growth hormone release through the ghrelin receptor rather than the GHRH receptor. Ipamorelin belongs here. Because the two classes use different doors, they are often discussed together.
GLP-1
glucagon-like peptide-1A gut hormone released after eating that reduces appetite, slows stomach emptying and prompts insulin release. The basis of the modern weight-loss drug class. See how GLP-1 peptides work.
Grey market
Trade that is not straightforwardly illegal but sits outside normal regulatory oversight. Most research peptide sales occur here, which is why product quality varies so much between suppliers.
Growth hormone
GH, somatropinA 191-amino-acid hormone from the pituitary, released in pulses and largest during deep sleep. Because it pulses, a single blood test of GH itself tells you very little — IGF-1 is measured instead.
Half-life
How long it takes for half of a compound to be cleared from the blood. It drives dosing frequency. Note that a short half-life does not always mean a short effect — some compounds trigger changes that outlast their own presence.
HbA1c
A blood test reflecting average blood sugar over roughly the previous three months. Because it averages, retesting sooner than about twelve weeks tells you little.
Human equivalent dose
HEDAn estimate of the human dose corresponding to one used in animals, calculated by scaling for body surface area rather than simply by weight. Mouse-to-human conversion divides by roughly twelve — which is why animal doses translate to much smaller human numbers than they first appear.
HPLC
high-performance liquid chromatographyThe standard technique for measuring purity. It separates a sample into its components and reports what fraction is the intended molecule. It confirms proportion, not identity — that requires mass spectrometry.
IGF-1
insulin-like growth factor 1A hormone produced largely by the liver in response to growth hormone. Because it is far more stable in blood than GH itself, it is the standard marker clinicians use to judge growth hormone activity.
Incretin
A gut hormone released in response to food that boosts insulin secretion. GLP-1 and GIP are the two main ones, and both underpin current metabolic drug development.
Insulin syringe
A fine-needled syringe marked in units rather than millilitres, used for most peptide injections. Barrel sizes vary; the unit scale does not. See dosing and injection basics.
Intramuscular
IMInjection into muscle, using a longer needle than subcutaneous. Rarely used for peptides, which are generally given into the fat layer instead.
Intranasal
Delivered as a spray into the nose, absorbing through the nasal lining. This is the route used in the Russian clinical work on Semax and Selank, which matters when comparing to injectable versions.
In vitro
Literally "in glass" — an experiment in cells or isolated tissue rather than a living organism. In vivo means in a living animal or person. An in vitro finding is a starting point, not evidence about people.
IU
international unitA measure of biological activity rather than weight, used for some hormones. It is not interchangeable with milligrams, and confusing the two is a recognised source of dosing error.
Joint pain
arthralgiaA recognised effect of growth-hormone-axis compounds, generally attributed to fluid retention in and around the joints. It typically appears early and often eases at lower exposure.
Kd
dissociation constantA number describing binding affinity. A lower Kd means tighter binding. It measures attachment strength, whereas EC50 measures how much effect follows.
kDa
kilodaltonOne thousand daltons. Used for larger molecules — proteins are usually described in kDa, short peptides in plain daltons.
LAL test
The standard assay for bacterial endotoxin in injectable products. If a certificate does not mention endotoxin or LAL, that testing was probably not done.
Ligand
Any molecule that binds to a receptor. A neutral term — it covers agonists, antagonists and anything else that attaches.
Lipidation
Attaching a fatty acid chain to a peptide so it binds to albumin in the blood and circulates far longer. This is the modification behind weekly rather than daily dosing in several approved drugs.
Lipohypertrophy
A firm, rubbery thickening of fat tissue caused by injecting the same small area repeatedly. It is not just cosmetic — the damaged tissue absorbs unpredictably, so identical doses can behave differently. Poor site rotation and needle reuse are the main causes.
Loading phase
An initial period at a higher frequency or amount, followed by a lower maintenance schedule. Common in community protocols; rarely derived from published trials.
Lyophilized
freeze-driedWater removed under vacuum at low temperature, leaving a dry powder that is far more stable than a solution. Almost all research peptides ship this way and must be reconstituted before use.
Mass spectrometry
MS, LC-MSThe technique confirming what a molecule actually is, by measuring its mass. Purity testing tells you how much of the sample is one thing; mass spectrometry tells you whether that thing is what the label claims.
Melanocortin receptors
MC1R–MC5RA family of five receptors. MC1R governs pigmentation, MC3R and MC4R affect appetite and sexual arousal, MC5R relates to sebaceous glands. A compound hitting several of them produces effects across all those systems at once.
Meta-analysis
A study that statistically pools results from multiple earlier trials to get a more reliable overall estimate. Generally stronger evidence than any single trial — though only as good as the studies it combines.
Metabolite
What a compound becomes after the body starts breaking it down. Some metabolites are inactive; some are active in their own right. Bremelanotide is a metabolite of Melanotan II.
mcg
microgram, µgOne thousandth of a milligram. 1 mg = 1,000 mcg. Confusing the two is the most common and most consequential arithmetic error in peptide use.
Multi-dose vial
A vial designed to be entered more than once, which is only safe when the solution contains a preservative. Bacteriostatic water carries a 28-day in-use window from first puncture.
NAD+
A coenzyme central to energy metabolism and to a family of repair and signalling enzymes. Levels decline with age, which is why it appears constantly in longevity discussion. See NAD+ injections explained.
N-terminus
The starting end of a peptide chain; the other end is the C-terminus. Sequences are conventionally written N-terminus first, and many enzymes attack from one specific end.
Nootropic
A loose label for anything claimed to improve cognition. It describes an intention rather than a mechanism or an evidence standard, and covers everything from caffeine to unstudied research compounds.
n
The number of participants in a study. A result from n=6 and a result from n=6,000 are not comparable, and a great deal of peptide research sits at the small end.
Off-label
Prescribing an approved medicine for a purpose other than its approved one. Legal and common in medical practice. It applies only to approved drugs — an unapproved compound cannot be used off-label, because there is no label.
Oligopeptide
A short peptide, conventionally under about twenty amino acids. The boundaries between oligopeptide, polypeptide and protein are conventions rather than biological facts.
Open-label
A study where everyone knows who is getting what. Easier to run and far weaker as evidence, because expectation affects both participants and assessors. Several impressive-looking peptide results come from open-label studies.
Oxidation
A degradation reaction that damages certain amino acids on exposure to air, light or heat. One of the reasons vials are sealed, shielded from light and kept cold.
PEGylation
Attaching polyethylene glycol chains to a molecule to slow its clearance and extend its duration. An alternative strategy to lipidation for the same problem.
Peptide
A chain of amino acids joined by peptide bonds, conventionally up to around fifty of them. Longer chains that fold into stable shapes are called proteins. The line is a naming convention, not a biological switch.
Peptide bond
The chemical link joining one amino acid to the next, formed by releasing a water molecule. It is the backbone of every peptide and protein.
Peptidase
proteaseAn enzyme that cuts peptides apart. Your body is full of them, which is why unmodified peptides survive minutes rather than hours and why swallowing them mostly does not work.
Pharmacodynamics
PDWhat the drug does to the body — which receptors it hits and what follows. The companion to pharmacokinetics, which is what the body does to the drug.
Pharmacokinetics
PKWhat the body does to the drug: absorption, distribution, metabolism and elimination. Half-life, Cmax and bioavailability are all PK measures.
Phase 1, 2, 3
The stages of human drug testing. Phase 1 checks safety in a small group; Phase 2 looks for efficacy and workable dosing; Phase 3 is the large controlled trial that supports approval. Most research peptides have never reached Phase 1.
Placebo
An inactive comparison treatment. Placebos produce real measurable improvements, particularly in subjective outcomes — which is precisely why a study without one cannot tell you much.
Polypeptide
A longer amino acid chain, roughly above twenty residues. Every protein is a polypeptide; not every polypeptide has folded into a protein.
Preclinical
Research done before any human testing — cells, tissue and animals. Necessary groundwork, and not evidence that something works in people.
Purity
The percentage of a sample that is the intended peptide, usually by HPLC. The remainder is typically truncated chains left over from synthesis. Purity says nothing about identity or about endotoxin.
p-value
A statistic estimating how likely a result this extreme would be if the treatment did nothing. Below 0.05 is the conventional threshold for "statistically significant" — which indicates detectability, not importance.
Quality control
QCThe testing a manufacturer performs to confirm a batch meets specification. In regulated manufacturing it is mandatory and documented; for research compounds it is entirely at the supplier's discretion.
Randomised controlled trial
RCTA study where participants are assigned by chance to treatment or control. Randomisation is what makes the groups comparable, and it is the design most peptide claims are missing.
Receptor
A protein, usually on a cell surface, that recognises a specific molecule and triggers a response when it binds. Peptides work by fitting receptors — which is why a small change to a sequence can change everything.
Reconstitution
Dissolving lyophilized powder in liquid to make an injectable solution. How much liquid you add sets the concentration and therefore how far along the syringe you draw.
Residue
An individual amino acid within a chain. A "fifteen-residue peptide" has fifteen amino acids in it.
Research use only
RUOA labelling statement meaning the seller is not claiming the product is fit for human use. It is a legal position, not a safety classification, and it does not indicate that anything was tested or cleared. See research vs pharmaceutical peptides.
Rotation
site rotationSystematically moving injection sites so no small area is used repeatedly. It is the main defence against lipohypertrophy, and structured rotation works far better than choosing at random.
Secretagogue
A substance prompting the body to release its own hormone, rather than supplying that hormone from outside. A growth hormone secretagogue tells your pituitary to release GH; it is not GH itself.
Selectivity
How narrowly a compound hits its intended target. High selectivity means fewer off-target effects. Low selectivity is often the direct explanation for a long side-effect list.
Sequence
The order of amino acids in a peptide, written from N-terminus to C-terminus. It determines the shape, and the shape determines what the molecule does.
Solubility
How readily a compound dissolves. Most peptides dissolve straightforwardly in bacteriostatic water; a few need a different solvent, which is worth checking before opening the vial.
Somatostatin
The hormone that brakes growth hormone release. Because it works against GH, compounds that suppress somatostatin can raise GH indirectly.
Solid-phase peptide synthesis
SPPSThe dominant manufacturing method: the chain is built one amino acid at a time on a resin bead, then cut off. Each coupling step is efficient but imperfect, which is where truncated impurities come from.
Stacking
Running two or more compounds together. Common practice, almost never studied, and it makes attributing any effect — good or bad — to a particular compound impossible.
Steady state
The point at which the amount going in each dosing interval matches the amount being cleared, so levels stop climbing. Usually reached after about four to five half-lives, which is why early readings can mislead.
Sterile water
Water for injection with no preservative. Suitable for a single use only, because nothing in it prevents bacterial growth once the vial has been entered.
Subcutaneous
SC, SubQInto the fat layer just beneath the skin — the standard route for peptides. Absorption is slower and steadier than intramuscular, and the needle required is short and fine.
Systematic review
A structured survey of all the research on a question using pre-declared criteria, rather than a selective summary. Often paired with a meta-analysis.
Tachyphylaxis
A rapid drop in response after repeated doses, occurring over hours or days rather than weeks. Faster and more abrupt than ordinary tolerance.
TFA
trifluoroacetateA residue left over from the acid used to release finished peptides from the synthesis resin. It can carry through into the product unless a salt exchange is performed, and is one of the impurities good manufacturing controls for.
Titration
Adjusting a dose gradually to find the balance between effect and tolerability. Upward titration is standard for GLP-1 medicines specifically because starting at the target amount causes nausea severe enough to make people quit.
Tmax
How long after dosing the peak blood concentration occurs. Together with Cmax it describes the shape of the rise.
TUE
therapeutic use exemptionFormal permission for an athlete to use an otherwise prohibited substance for a documented medical need. It must be granted in advance, and unapproved substances generally do not qualify.
Units
The markings on an insulin syringe. On the standard U-100 scale, 100 units is 1 ml, so 20 units is 0.2 ml. Units measure volume, not milligrams — the same unit mark delivers different amounts of peptide depending on how you reconstituted.
USP
United States PharmacopeiaThe body setting quality standards for medicines and compounding in the US. Its chapters define things like sterile preparation requirements and in-use periods for multi-dose vials.
Vasoactive
Affecting blood vessel diameter and therefore blood pressure and flow. Vasoactive compounds commonly cause flushing, and warrant particular care for anyone with cardiovascular history.
Vial
The sealed glass container peptides ship in, closed with a rubber stopper you draw through rather than remove. Standard peptide vials hold 3 ml, which is the practical ceiling on how much water you can add.
WADA
World Anti-Doping AgencyThe body publishing the Prohibited List used in tested sport. Its S0 category captures any substance with no approval from any government health authority — which describes most research peptides, whether or not they are named individually.
Washout period
A deliberate break long enough for a compound to clear completely. Used in crossover trials to stop one phase contaminating the next, and useful personally for testing whether an effect was real.
X-ray crystallography
A technique for determining a molecule's three-dimensional structure by crystallising it and analysing how it scatters X-rays. It is how researchers work out the shapes that explain receptor binding.
Yield
The proportion of theoretical maximum product a synthesis actually produces. Long peptides have lower yields because small failures at each step compound — which is part of why longer sequences cost more.
Z-score
also SDS, standard deviation scoreA way of expressing a lab result relative to the normal range for your age and sex, rather than as a raw number. IGF-1 is commonly reported this way, because what counts as normal shifts substantially with age.
Common Questions
What is the difference between a peptide and a protein?
Chain length, by convention rather than biology. Peptides are generally under about fifty amino acids; longer folded chains are called proteins. Sources put the line anywhere between forty and a hundred, and insulin at fifty-one residues gets called both.
Why are doses in mcg when vials are in mg?
Because many peptides are active at very small amounts, and writing 0.00025 g is unworkable. The conversion is 1 mg = 1,000 mcg. Mixing the two up by a factor of a thousand is the most consequential arithmetic error in this field.
What is the difference between purity and identity testing?
Purity, by HPLC, tells you what proportion of a sample is a single dominant substance. Identity, by mass spectrometry, tells you whether that substance is the one on the label. A product can be 99% pure and 100% the wrong compound.
Does "research use only" mean it has been tested?
No — that reading is exactly backwards. It means the seller is not claiming the product is fit for human use, which removes obligations that would otherwise apply. It is a legal position, not a certification.
Why do units and millilitres get confused?
Because insulin syringes are marked in units, since that is how insulin is dosed. On a U-100 syringe, 100 units is 1 ml. The units mean nothing about how many milligrams you are drawing — that depends entirely on how much water you added.
Is there a term I should know that isn't here?
Quite possibly — this covers the vocabulary that recurs across guides, labels and papers, not every term in peptide chemistry. Message us with anything you have hit that is not defined here and we will add it.
Hit a term that still doesn't make sense?
Send it to us and we'll explain it plainly — and add it to this page if it's one other people are likely to run into too.
Contact Us on WhatsAppImportant disclaimer: This glossary is general educational content only. It is not medical advice, a prescription, or a personalized recommendation. Definitions are written for general comprehension and are necessarily simplified; technical terms carry more precise meanings in scientific and regulatory contexts, and usage varies between disciplines and publications. Several boundaries described here — including the distinction between peptides and proteins — are naming conventions rather than fixed biological or legal definitions, and different sources draw them differently. No dosing figures appear on this page by design, and inclusion of a term does not imply that any compound associated with it is safe, effective, legal or appropriate for any individual. Most peptides sold by Peptides Costa Rica are not approved by the FDA, the EMA, or Costa Rica's Ministerio de Salud as finished pharmaceutical drugs for human use and are sold as research compounds intended for laboratory and scientific study. Regulatory terminology reflects the position at the time of writing and may change. Always consult a qualified healthcare professional before beginning any peptide protocol. Products sold by Peptides Costa Rica are intended for laboratory and research purposes only.
- National Human Genome Research Institute and StatPearls (National Institutes of Health): Standard definitions of amino acids, peptides and the conventional chain-length boundaries between peptides, polypeptides and proteins.
- IUPAC Compendium of Chemical Terminology: Reference definitions for chemical terms including peptide bond, chirality, isomerism and molecular mass units.
- United States Pharmacopeia: Standards covering sterile compounding, bacteriostatic water composition, multi-dose vial in-use periods and analytical procedure validation.
- U.S. Food and Drug Administration: Definitions relating to drug approval phases, 503A and 503B compounding, bulk drug substances lists, and the interpretation of protein versus peptide for regulatory purposes.
- World Anti-Doping Agency: Prohibited List structure, the S0 non-approved substances category, and therapeutic use exemptions.
- Clinical pharmacology reference literature: Standard definitions of pharmacokinetic and pharmacodynamic parameters including half-life, Cmax, Tmax, AUC, steady state, bioavailability, EC50 and dissociation constant.
- Published injection technique consensus recommendations: Terminology relating to subcutaneous administration, needle gauge, site rotation and lipohypertrophy.
