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Glossary

Every word we use, defined once.

The regulatory vocabulary of compounding and the pharmacology our monographs run on, in one plain-English list. Definitions only. Nothing here says what a molecule does for you or whether you can get it — that lives on the molecule's own page.

78 terms51 plain-English scienceEighth-grade reading level
78 of 78

Six distinctions the category keeps collapsing

Most explainers get the buckets right and the consequences wrong. These six carry a plain statement of the wrong reading, and then the correction.

#

503A

Regulatory#

A pharmacy that compounds a medication for one named patient against a prescription, under section 503A of the federal drug law.

Most peptide compounding people ask about would happen here, and only for substances the law lets a 503A pharmacy use.

Full explanation · 503A vs 503B, and the three doors

503B

Regulatory#

An outsourcing facility that compounds in batches for clinics to keep on hand, registered with the FDA and inspected against manufacturing standards.

A 503B batch can exist without a prescription in hand; the substances it may use are a different list from 503A's.

Full explanation · 503A vs 503B, and the three doors

“503B registered”

Regulatory#

The FACILITY is registered with the FDA as an outsourcing facility — the DRUG it makes is not FDA-approved.

Not the same as Commonly confused with: the drug being FDA-approved, or the formula having been reviewed. Neither follows. Registration is a status held by a building and a company, not by a product. Conflating the two is the single most common error in this category.

Full explanation · 503A vs 503B, and the three doors
A

agonist

Science#

A molecule that switches a receptor on, the way the body's own signal would.

Appears on: Semaglutide, Tirzepatide

amino acid

Science#

One of the small building blocks the body strings together to make peptides and proteins.

amylin

Science#

A hormone released with insulin that slows digestion and signals fullness.

Appears on: Cagrilintide

analog

Science#

A molecule built to closely resemble a natural one, with small changes — often to make it last longer or bind more tightly.

Appears on: Sermorelin, Tesamorelin

angiogenesis

Science#

The growth of new small blood vessels into a tissue.

It is a repair mechanism, and it is also why a molecule that drives it gets asked about carefully in anyone with a cancer history.

Appears on: BPC-157, TB-500

animal-dominant evidence

Science#

A body of research made up mostly of animal studies, with few or no human trials behind it.

It is the most common evidence state in this category, and it is why so many grades sit low.

Appears on: BPC-157, TB-500, Epitalon

apoptosis

Science#

The body's orderly way of shutting a cell down and clearing it away.

Appears on: FOXO4-DRI, Epitalon
B

banned in sport

Science#

On the World Anti-Doping Agency's prohibited list, so a tested athlete who uses it can be sanctioned.

Appears on: BPC-157, TB-500

bioavailability

Science#

How much of a substance actually reaches your bloodstream after you take it.

Most peptides are destroyed by digestion, which is why swallowing them rarely works.

Appears on: BPC-157, Semax

bioregulator

Science#

A term used by a Russian research school for very short peptides claimed to regulate specific organs.

Western validation is thin, and we say so on each one.

Appears on: Epitalon, Vilon, Pinealon

bulks list

Regulatory#

The list of bulk drug substances a compounder is allowed to start from, kept separately for 503A and 503B.

A peptide with no bulks-list entry has no legitimate starting material for a compounder to use.

Full explanation · Category 1 vs 2 vs 3, explained
C

cardiolipin

Science#

A fat molecule in the inner membrane of your mitochondria.

Some peptides are studied because they bind to it.

Appears on: SS-31 / Elamipretide

Category 1

Regulatory#

The FDA's bucket for bulk substances it considers eligible for enforcement discretion while their nomination is evaluated.

Not the same as Commonly confused with: FDA approval, and with a statement that the substance works. It is neither. Category 1 is a queue position, not a verdict on safety or efficacy.

Full explanation · Category 1 vs 2 vs 3, explained

Category 2

Regulatory#

The FDA's bucket for bulk substances it has identified significant safety risks with, which it does not intend to allow in compounding.

Full explanation · Category 1 vs 2 vs 3, explained

Category 3

Regulatory#

The FDA's bucket for nominated substances whose paperwork was too incomplete to evaluate.

Full explanation · Category 1 vs 2 vs 3, explained

cathelicidin

Science#

A family of natural antimicrobial peptides the body makes as part of its first-line defence.

Appears on: LL-37

certificate of analysis

Regulatory#

A lab document stating what a specific batch was tested for and what the results were.

It is only as good as who ran the tests and which tests they ran — a certificate is a document, not a guarantee.

Full explanation · Research grade vs human grade

cGMP

Regulatory#

Current Good Manufacturing Practice — the enforceable standards a facility follows so every batch is made the same way and documented.

Full explanation · Research grade vs human grade

clinical need

Regulatory#

A documented reason the approved product cannot meet a patient's need — an allergy to an inactive ingredient, or a strength that is not made.

Not the same as Commonly confused with: cost, insurance denial, or convenience. The FDA has stated that affordability and insurance coverage do not constitute clinical need.

Full explanation · 503A vs 503B, and the three doors

clinician of record

Regulatory#

The named, licensed prescriber responsible for a specific patient's care and for the prescription itself.

It is the third door: without a clinician taking that responsibility, nothing legitimate is being prescribed.

Full explanation · Are peptides legal? The three-door test

compounded

Regulatory#

Made to order by a pharmacy for a specific patient or clinic, rather than manufactured as an approved product — compounded medications are not FDA-approved.

Nothing about a compounded preparation has been reviewed by the FDA for safety, efficacy or quality.

Full explanation · 503A vs 503B, and the three doors

compounding

Regulatory#

The practice of combining, mixing or altering ingredients to create a medication for an individual patient.

Full explanation · 503A vs 503B, and the three doors

copper peptide

Science#

A short peptide bound to a copper atom, studied in skin repair and used in cosmetic formulations.

Appears on: GHK-Cu (topical)

cytoprotective

Science#

Protecting cells from damage, rather than making new tissue.

Appears on: BPC-157, KPV
E

endotoxin

Science#

A toxic fragment left behind by dead bacteria, which can cause fever and worse even when nothing living remains.

enforcement discretion

Regulatory#

The FDA signalling that it does not currently intend to act against a compounder over a substance, provided the other conditions are met.

Not the same as Commonly confused with: approval. It is not approval. No review of safety, efficacy or manufacturing has taken place, and the position can change without a rule changing.

Full explanation · Category 1 vs 2 vs 3, explained

essentially a copy

Regulatory#

A compounded preparation that is close enough to an approved commercial product that the law does not allow it to be compounded.

It is the test that decides whether a compounded version of an approved drug may exist at all.

Full explanation · 503A vs 503B, and the three doors
G

ghrelin receptor

Science#

The docking point for ghrelin, the hunger signal, which also triggers a growth-hormone pulse when it is switched on.

Appears on: Ipamorelin, MK-677 (Ibutamoren), Hexarelin

GHRH analog

Science#

A copy of the brain signal that tells the pituitary gland to release growth hormone.

Appears on: Sermorelin, Tesamorelin, CJC-1295

GIP

Science#

A second gut hormone in the same family as GLP-1, acting on a different receptor.

Appears on: Tirzepatide, Retatrutide

GLP-1

Science#

One of the gut hormones released after a meal; it slows the stomach, signals fullness, and prompts insulin release.

Appears on: Semaglutide, Tirzepatide, Orforglipron

GnRH

Science#

The brain signal that tells the body to make sex hormones.

Appears on: Gonadorelin, Triptorelin, Kisspeptin
H

half-life

Science#

How long it takes the body to clear half of a substance from the blood.

It is the main reason two molecules aimed at the same target are taken on completely different schedules.

Appears on: CJC-1295, Ipamorelin
I

identity testing

Science#

Confirming that what is in the vial is the substance the label names, and not something else.

IGF-1

Science#

A growth signal made mostly by the liver in response to growth hormone; it is what actually reaches most tissues.

Appears on: IGF-1 LR3, PEG-MGF / MGF, Sermorelin

incretin

Science#

A gut hormone released when you eat that tells the pancreas to release insulin.

Appears on: Semaglutide, Tirzepatide, Retatrutide

IND

Regulatory#

An Investigational New Drug application — the FDA filing that lets a sponsor give an unapproved substance to people in a trial.

Full explanation · The FDA Peptide Tracker

intranasal

Science#

Given as a spray into the nose, so the lining of the nose absorbs it.

Appears on: Semax, Selank, PT-141

investigational

Regulatory#

A substance still in clinical study, which may be given to people only inside an authorised trial.

Full explanation · The FDA Peptide Tracker
K

Khavinson class

Science#

The group of very short peptides described by the Russian researcher Vladimir Khavinson and his colleagues.

Nearly all of the published work comes from one research lineage, which is a limit on the evidence, not a detail.

Appears on: Epitalon, Vilon, Pinealon
M

mechano-growth factor

Science#

A version of IGF-1 that muscle produces locally after it has been stressed or damaged.

Appears on: PEG-MGF / MGF

melanocortin

Science#

A family of body signals involved in skin pigment, inflammation, appetite and sexual arousal.

Appears on: PT-141

mitochondrial-derived peptide

Science#

A short peptide encoded inside the mitochondria's own DNA rather than the cell's.

Appears on: MOTS-c, Humanin

mTOR

Science#

A control switch inside cells that decides whether to grow and build or to conserve and recycle.

Appears on: Rapamycin, Metformin

myostatin

Science#

A body signal that puts a ceiling on muscle growth.

Appears on: Follistatin-344
N

neurotrophic

Science#

Supporting the survival, growth or repair of nerve cells.

Appears on: Cerebrolysin, Dihexa, PE-22-28

NNMT

Science#

An enzyme that uses up part of the raw material cells need for NAD+ production.

Appears on: 5-Amino-1MQ

nootropic

Science#

A substance taken in the hope of improving memory, focus or mental stamina.

Appears on: Semax, Selank, Cerebrolysin
O

off-label

Regulatory#

Prescribing an approved drug for a use, group or route that is not on its approved labelling.

It is legal medical practice and it is not the same thing as compounding an unapproved substance.

Full explanation · Are peptides legal? The three-door test

outsourcing facility

Regulatory#

The formal name for a 503B compounder.

Full explanation · 503A vs 503B, and the three doors
P

PCAC

Regulatory#

The Pharmacy Compounding Advisory Committee, an outside panel that advises the FDA on which bulk substances belong on the compounding lists.

Full explanation · What a PCAC “yes” actually buys

PCAC recommendation

Regulatory#

A vote by the advisory committee. It is advisory only — FDA rulemaking must follow before anything changes in practice.

Not the same as Commonly confused with: approval, authorisation to compound, and a change in what a pharmacy may actually make. It is none of the three. The FDA is not bound by the vote, and the rulemaking that would give it effect takes its own course.

Full explanation · What a PCAC “yes” actually buys

peptide

Science#

A short chain of amino acids — smaller than a protein, and usually built to act like a signal in the body.

Some things people call peptides are not peptides at all, and we label those plainly on the molecule's own page.

Appears on: BPC-157, MK-677 (Ibutamoren)

Phase 1 / 2 / 3

Regulatory#

The three stages of human trials: first safety in a small group, then whether it works in a larger one, then confirmation at scale.

A molecule in Phase 3 is still investigational; the phase describes progress, not permission.

Full explanation · The FDA Peptide Tracker

placebo-controlled

Science#

A study where some people get the real thing and others get a look-alike with nothing in it, so the effect can be separated from expectation.

Appears on: BPC-157, Semaglutide

potency

Science#

Whether a vial actually contains the amount of substance its label claims.

Appears on: BPC-157

preclinical

Science#

Research done before humans — in cells, tissue or animals.

Appears on: TB-500, MOTS-c
R

receptor

Science#

A docking point on a cell that changes what the cell does when the right molecule attaches to it.

removal from Category 2

Regulatory#

The FDA taking a substance out of the bucket it had flagged for safety risk.

Not the same as Commonly confused with: placement in Category 1, and with permission to compound. It is neither. Removal from Category 2 changes one classification and authorises nothing.

Full explanation · Category 1 vs 2 vs 3, explained

research use only

Science#

A label that lets a seller skip FDA oversight, sterility testing and manufacturing standards by declaring the product is not for humans.

It transfers the entire risk to the buyer.

Appears on: BPC-157, IGF-1 LR3

rulemaking

Regulatory#

The formal process by which the FDA writes a change into the rules, including public notice and comment.

It is the step between an advisory vote and anything a pharmacy may actually do, and it is measured in months to years.

Full explanation · What a PCAC “yes” actually buys
S

secretagogue

Science#

A substance that prompts your body to release something it already makes, rather than supplying it directly.

Growth-hormone secretagogues nudge your own production instead of adding external hormone.

Appears on: Ipamorelin, MK-677 (Ibutamoren), Hexarelin

senescent cell

Science#

A cell that has stopped dividing, refuses to die, and leaks signals that irritate the tissue around it.

Appears on: FOXO4-DRI

senolytic

Science#

A substance studied for clearing out worn-out cells that have stopped dividing but have not died.

Appears on: FOXO4-DRI

shortage list

Regulatory#

The FDA's published list of drugs in short supply, which temporarily widens what compounders may make.

Coming off that list closes the opening again, which is the mechanism behind the compounded GLP-1 wind-down.

Full explanation · 503A vs 503B, and the three doors

splice variant

Science#

A different version of a protein the body builds from the same gene by reading its instructions differently.

Appears on: PEG-MGF / MGF

state board of pharmacy

Regulatory#

The state agency that licenses pharmacies and pharmacists and can act against them, alongside federal rules.

It is the second door: a substance can clear federal questions and still be limited by the state you are in.

Full explanation · Are peptides legal? The three-door test

sterility

Science#

Whether a product is free of living microbes — the thing that matters most for anything injected.

subcutaneous

Science#

Into the layer of fat just under the skin, rather than into a muscle or a vein.

Appears on: Sermorelin, Semaglutide
T

third-party batch testing

Science#

Testing of a specific batch by a lab that did not make it and does not profit from selling it.

thymic peptide

Science#

A peptide originally identified in the thymus, the gland that trains immune cells.

Appears on: Thymosin Alpha-1, Thymalin

TREK-1

Science#

A channel in brain cells that has been studied as a target in depression.

Appears on: PE-22-28

troche / ODT

Science#

A lozenge or fast-dissolving tablet held in the mouth so the lining of the mouth absorbs it instead of the stomach.

U

USP monograph

Regulatory#

A published quality standard for a substance — what it must contain, how pure it must be, and how to test it.

Its absence is one of the reasons a substance can sit outside compounding eligibility for years.

Full explanation · Category 1 vs 2 vs 3, explained
W

WADA S0 / S2

Science#

Two categories on the World Anti-Doping Agency's prohibited list: S0 covers substances with no approval for human use anywhere, S2 covers hormones and growth factors.

Appears on: BPC-157, TB-500, Ipamorelin
Maintained by the Peptós.LIFE editorial team · Last updated June 2026. Definitions are educational, not medical advice, and not a statement about any molecule's status or availability. Compounded medications are not FDA-approved.
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