Reference
Glossary
The vocabulary of peptide research, defined plainly. Every term links to a fuller plain-English explanation — no biochemistry degree required.
107 terms
Pharmacology
- Adverse event
- An adverse event is anything harmful recorded during a trial, whether or not the drug caused it — which is why placebo groups report them too.
- Agonist
- An agonist is a molecule that binds a receptor and switches it on, triggering the same response the body's own signal would.
- Analog (analogue)
- An analog is a molecule built to closely resemble another, with small changes that improve how it works — often longer-lasting or more potent.
- Antagonist
- An antagonist binds a receptor but doesn't switch it on — it blocks the receptor so the body's natural signal can't get through.
- Binding affinity
- Binding affinity is how tightly a molecule holds onto its binding partner, such as a peptide binding to a receptor.
- Bioavailability
- Bioavailability is the fraction of a dose that actually reaches your bloodstream intact — and it's why most peptides are injected, not swallowed.
- cAMP
- cAMP is a messenger molecule inside cells that relays a receptor's signal into actual cell activity.
- Clearance
- Clearance is how quickly your body removes a compound from the blood — the underlying rate that sets a drug's half-life.
- Contraindication
- A contraindication is a specific reason a drug should not be used in a particular person — a hard no, not a caution.
- dose-dependent
- dose-dependent means an observed effect changes when the dose changes; a stronger effect at higher doses is one common pattern.
- DPP-4
- DPP-4 is an enzyme that rapidly clips and inactivates natural GLP-1, limiting how long the hormone can signal.
- Dual and triple agonists
- A dual agonist activates two different receptors at once; a triple agonist activates three — the design behind newer metabolic peptides.
- Efficacy
- Efficacy is how large an effect a treatment can produce under ideal trial conditions — separate from potency, which is how much dose that takes.
- Endogenous
- Endogenous means produced inside your own body; exogenous means introduced from outside, like an injection.
- Endogenous vs exogenous
- Endogenous means made inside the body or cell; exogenous means supplied from outside that body or cell.
- Half-life
- Half-life is the time it takes for half of a substance to clear from your body — a quick guide to how long its effect lasts and how often to dose.
- Ligand
- A ligand is a molecule that binds a biological target such as a receptor; binding alone does not say whether it activates or blocks the target.
- Metabolite
- A metabolite is what is left after your body breaks a compound down — sometimes inert, sometimes still active in its own right.
- Nootropic
- A nootropic is a compound claimed to improve memory, focus, or learning; the label alone does not prove efficacy, safety, or approval.
- Pharmacodynamics
- Pharmacodynamics is what a drug does to your body — the effects it produces — the mirror image of pharmacokinetics.
- Pharmacokinetics
- Pharmacokinetics is what your body does to a compound — how it's absorbed, distributed, broken down, and cleared over time.
- Potency
- Potency is how much dose a compound needs to produce its effect — a potent drug works at a small dose, which is not the same as working better.
- Pulsatile release
- Pulsatile release means a hormone comes out in bursts separated by quieter periods, rather than flowing at a constant rate.
- Receptor
- A receptor is a protein on or inside a cell that a specific molecule locks onto, triggering a response — the lock that a peptide 'key' fits.
- Receptor desensitization
- Receptor desensitization is a cell reducing its response after repeated stimulation, so the same signal produces less effect.
- Receptor desensitization
- Desensitization is receptors dialling down their response to constant stimulation, so the same dose produces less effect over time.
- Receptor selectivity
- Receptor selectivity is how strongly a compound prefers its intended receptor over other receptors at the same concentration.
- Receptor selectivity
- Selectivity is how narrowly a compound hits its intended receptor instead of several — the usual explanation for fewer off-target effects.
- Secretagogue
- A secretagogue is a substance that tells a gland to release (secrete) its own hormone — instead of adding that hormone from outside the body.
- senolytic
- A senolytic is a compound designed to selectively clear senescent cells that stopped dividing but remain active.
- Steady state
- Steady state is the dosing plateau where the amount of drug entering the body matches the amount cleared, so average blood levels stop rising.
- Systemic
- Systemic means a compound reaches the bloodstream and acts throughout the body, rather than staying where it was applied.
- Systemic vs local effect
- The systemic vs local effect distinction tells whether a substance acts across the body or mainly at the place where it was applied.
- Tolerability
- Tolerability is how manageable a treatment's observed side effects are for the people receiving it.
- Tolerance
- Tolerance is when the same dose produces less effect over time, so more is needed to get what the first dose gave.
Delivery & dosing
- Bacteriostatic water
- Bacteriostatic water is sterile water with 0.9% benzyl alcohol added to stop bacterial growth — the usual liquid for reconstituting peptides.
- Blood-brain barrier
- The blood-brain barrier is a selective filter around brain blood vessels; a molecule must cross or bypass it to act directly in brain tissue.
- Depot injection
- A depot is a slow-release reservoir of drug left at the injection site that trickles into the blood over days or weeks.
- Intramuscular injection
- An intramuscular injection goes deep into a muscle, where rich blood flow absorbs it faster than a shot under the skin.
- Intranasal
- Intranasal means delivered as a spray or drops into the nose, absorbed through the nasal lining instead of swallowed or injected.
- Needle gauge
- Needle gauge measures a needle's outer thickness on a reverse scale: the higher the number, the thinner the needle.
- Reconstitution
- Reconstitution is mixing a freeze-dried peptide powder with a sterile liquid, usually bacteriostatic water, to make an injectable solution.
- Sterile water for injection
- Sterile water for injection is preservative-free water used to dissolve or dilute injectable drugs; once opened, the container is single-use.
- Subcutaneous injection
- A subcutaneous injection goes into the fat layer just under the skin, absorbed slowly and steadily — the most common route for peptides.
- Titration
- Titration means starting at a low dose and raising it in small steps, giving the body time to adjust and revealing side effects early.
- Topical
- Topical means applied to the skin surface — which is not the same as absorbed, since most peptides are too large to cross it passively.
Chemistry
- acetylation
- Acetylation adds a small chemical group to a peptide, often capping its N-terminus and making that end harder for enzymes to attack.
- Amino acid
- An amino acid is one of roughly 20 building blocks your body links in a precise order to make peptides and proteins.
- Amino acid sequence
- An amino acid sequence is the exact order of amino acids in a peptide or protein — and that order determines its shape and what it does.
- Amino acid side chain
- An amino acid side chain, or R group, is the variable chemical branch that gives each amino acid its identity and behavior.
- DAC peptide
- DAC (Drug Affinity Complex) is a chemical handle that latches a peptide onto blood albumin so it lasts days instead of minutes.
- Disulfide bond
- A disulfide bond is a chemical clip between two cysteines that locks a peptide into its working shape — break it and activity is usually lost.
- Drug affinity complex (DAC)
- A drug affinity complex (DAC) is an add-on that binds a peptide to blood albumin so it lasts days instead of minutes.
- Essential amino acid
- An essential amino acid is one your body cannot synthesize in enough quantity, so you must get it from food.
- HPLC
- HPLC separates a sample into its components to measure how much of it is the intended peptide — the source of the purity percentage on a COA.
- L-form amino acid
- An L-form amino acid is the mirror-image form biology usually uses to build proteins; the L names its three-dimensional arrangement.
- Lipidation
- Lipidation attaches a fatty acid chain to a peptide so it binds albumin and can remain in circulation much longer.
- Lyophilized (freeze-dried)
- Lyophilized means freeze-dried — water is removed under vacuum, leaving a stable powder that must be mixed with liquid before it can be used.
- Mass spectrometry
- Mass spectrometry weighs a molecule to confirm its identity — the COA test that checks you got the right peptide, not just a pure one.
- Molecular formula
- A molecular formula lists exactly which atoms a molecule contains and how many of each — its fingerprint, where molecular weight is just the total.
- Molecular weight
- Molecular weight is the mass of one molecule, usually given in daltons — for peptides it roughly tracks how many amino acids are in the chain.
- N-terminus and C-terminus
- A peptide has two ends — the N-terminus (start) and C-terminus (finish) — and sequences are written from N to C.
- N-terminus and C-terminus
- The N-terminus is a peptide's free amino end; the C-terminus is its free carboxyl end. Sequences are written from N to C.
- N-terminus and C-terminus
- Every peptide chain has two ends — the N-terminus and the C-terminus — and sequences are always written from N to C.
- Net peptide content
- Net peptide content is the share of vial powder that is peptide rather than counterion salt, water, or other non-peptide material.
- Peptide
- A peptide is a short chain of amino acids linked together — the same building blocks as proteins, just far fewer of them.
- Peptide acetate
- Peptide acetate is a peptide paired with acetate counterions; unless content is stated on a free-base basis, some powder mass is acetate.
- Peptide purity
- Purity is the share of detected material that is the target peptide—a peak-area percentage, not a measure of how much peptide is in the vial.
- Peptide vs protein
- Peptides and proteins are both chains of amino acids; the difference is size — peptides are short (roughly under 50), proteins are long and folded.
- Proteinogenic
- A proteinogenic amino acid is one that cells genetically encode and insert into proteins as ribosomes build them.
- Recombinant
- Recombinant means made by engineered living cells given the gene for a protein — the route used for larger molecules that are impractical to build chemically.
Regulatory
- Boxed warning
- A boxed warning is the FDA's strongest warning on a drug label — a serious risk flagged in a box, not a ban.
- Compounding (503A/503B)
- Compounding is a licensed pharmacy custom-making a medication for a specific need — 503A pharmacies serve one patient, 503B facilities make batches.
- Controlled substance
- A controlled substance is one the DEA places on a schedule with criminal penalties — a category most peptides do not sit in.
- Dietary supplement
- A dietary supplement is a swallowed product labeled to supplement the diet and containing at least one legally qualifying dietary ingredient.
- FDA bulks list
- The FDA bulks lists identify bulk drug substances that compounders may use under specific federal compounding pathways.
- FDA bulks list Category 2
- The FDA bulks lists sort substances compounders may use; Category 2 flags significant safety risks and gets no enforcement discretion.
- FDA warning letter
- An FDA warning letter states alleged legal violations and requests a reply; it is official FDA notice, not a court ruling or ban.
- Investigational drug
- An investigational drug is being formally studied in clinical trials but is not FDA-approved; the status is a stage, not a verdict.
- Off-label use
- Off-label means a doctor prescribing an FDA-approved drug for a use the FDA never approved — legal, common, and different from research-use-only.
- Research-use-only (RUO)
- Research-use-only means a product is sold only for laboratory research, not human or animal use — it isn't FDA-approved as a medicine.
- USADA
- USADA is the United States Anti-Doping Agency; it tests U.S. Olympic and Paralympic athletes and enforces WADA's Prohibited List.
- WADA Prohibited List peptides
- The WADA Prohibited List names substances banned in sport; peptide hormones and GH secretagogues sit in class S2.
General
- Biohacking
- Biohacking is self-directed experimentation on your biology, from tracking sleep to using research peptides outside a clinical trial.
- Biomarker
- A biomarker is something measurable — a blood level, a scan — used as a stand-in for an outcome that is harder or slower to measure.
- Certificate of analysis (COA)
- A certificate of analysis is a lab report on the identity, purity, and content of one tested batch of a product.
- Clinical trial endpoint
- A clinical trial endpoint is the specific, preplanned outcome used to judge what a study found.
- Clinical trial phases
- Clinical trials run in phases: Phase 1 tests safety and dose, Phase 2 tests whether it works, Phase 3 tests it against a comparator at scale.
- Crossover trial
- In a crossover trial, each participant receives both treatment and control in sequence, serving as their own comparison.
- Effect size
- Effect size is how large a difference or relationship actually was, separate from whether the result was statistically significant.
- Endotoxin
- Endotoxins are fever-causing fragments left behind by dead bacteria — a vial can be sterile and still contain them.
- Evidence tier
- An evidence tier ranks how solid a claim's proof is — from human randomized trials at the top down to animal, test-tube, and anecdotal reports.
- GLP-1
- GLP-1 is a gut hormone that boosts insulin, curbs appetite, and slows digestion — the target drugs like semaglutide mimic for diabetes and weight loss.
- In vitro vs in vivo
- In vitro means in a dish or test tube; in vivo means in a living body. A result in isolated cells doesn't always hold up in a whole organism.
- Incretin
- Incretins are gut hormones released after you eat that signal the pancreas to release insulin — GLP-1 and GIP are the two main ones.
- Meta-analysis
- A meta-analysis statistically combines compatible results from multiple studies into one weighted estimate.
- Microgram
- A microgram (mcg) is one thousandth of a milligram, a mass unit common in peptide dosing where an mg/mcg mix-up creates a 1,000-fold error.
- n=1
- In research, n counts the subjects studied; n=1 means one person's experience—real information about them, but proof of nothing general.
- Observational study
- Researchers watch what people already do rather than assigning treatment, so the study can find associations but cannot prove cause.
- Open-label study
- In an open-label study everyone knows who received the drug, so expectation can inflate results — especially subjective ones like pain or mood.
- Peer review
- Peer review is expert assessment of a manuscript before publication to help an editor decide whether to publish it; it is a filter, not proof.
- Placebo
- A placebo is a dummy treatment given to a control group so researchers can separate a drug's real effect from expectation and time.
- Placebo effect
- The placebo effect is real symptom improvement driven by expectation and treatment context, not a treatment's specific active ingredient.
- Primary endpoint
- An endpoint is the specific outcome a trial set out to measure — and a biomarker endpoint is not the same as a result you would feel.
- Randomized controlled trial (RCT)
- A randomized controlled trial splits people randomly into treatment and control groups — the strongest way to prove a compound causes an effect.
- Sterility
- Sterility means the absence of viable microorganisms; for a vial, the claim requires separate microbiological evidence.
- Systematic review
- A systematic review gathers every study on a question by a set method; a meta-analysis pools their numbers into one estimate.