Peptide and GLP-1 glossary

The vial

Lyophilised

Freeze-dried under vacuum. The stable shipping form for research peptides — a dry pellet or film at the bottom of a sealed vial.

Reconstitution

Dissolving a lyophilised peptide in a diluent to produce a solution of known concentration. See reconstitution explained.

Bacteriostatic water

Sterile water containing 0.9% benzyl alcohol as a preservative, used for vials that will be accessed more than once.

Sterile water for injection

Water with no preservative, intended for single use. Not interchangeable with bacteriostatic water for multi-dose vials.

Diluent

Any liquid used to dissolve or dilute a product. For research peptides this is usually bacteriostatic water; approved products specify their own.

Concentration

Amount of substance per unit volume, e.g. mg/mL. For lyophilised vials you create it; for finished solutions the manufacturer sets it.

Beyond-use date (BUD)

The date assigned by a compounding pharmacy after which its preparation should not be used. Distinct from a manufacturer expiry date.

In-use window

How long a product remains usable after first puncture or first use, which is generally much shorter than the printed expiry.

Lot / batch number

The manufacturer's identifier for a production run. The single most useful thing to record for traceability.

Certificate of analysis (COA)

A document stating a batch's test results, such as purity by HPLC and identity by mass spectrometry. Its value depends entirely on the credibility of the testing laboratory.

The syringe

U-100

An insulin syringe calibrated so 100 units span 1 mL. One unit is therefore 0.01 mL of volume — not an amount of peptide.

U-40

A syringe calibrated at 40 units per mL, still used in some veterinary contexts. One unit is 0.025 mL.

Unit (syringe)

A volume marking on an insulin syringe. The most overloaded word in peptide logging — see reading an insulin syringe.

IU (International Unit)

A measure of biological activity rather than mass, used for some hormones and vitamins. Not the same thing as a syringe unit, despite the shared word.

Gauge

Needle thickness. Higher gauge numbers mean thinner needles; insulin syringes are typically in the 29–31G range.

Dead space

The small volume retained in a syringe and needle hub after the plunger is fully depressed. Low-dead-space designs reduce it.

Subcutaneous (SC / SubQ)

Into the fatty layer beneath the skin. The route used for most self-administered injectables discussed on this site.

Intramuscular (IM)

Into muscle tissue. A different route with different technique and different absorption.

The schedule

Titration

Stepping a medication's amount up (or down) over time according to a prescriber-directed schedule. See GLP-1 titration tracking.

Every-N-day

A schedule that repeats on a fixed interval rather than on weekdays. Unless N is 7, it drifts against the calendar — see every-N-day schedules.

Cycling / on-off

Alternating a period of use with a defined break, repeating. A schedule shape, described here descriptively rather than recommended.

Stack

Several separately supplied compounds used over the same period, each with its own vial and schedule. See blends and stacks.

Blend

A single vial containing more than one peptide, pre-mixed by the supplier at fixed ratios.

Backdating

Recording an entry with its actual past date and time rather than the moment you logged it. Essential to an accurate record.

Adherence

The proportion of scheduled entries actually taken. Only computable if skipped entries are recorded explicitly.

Half-life

The time for the amount of a substance in circulation to fall by half. It is what determines whether a schedule is daily or weekly.

Pharmacology

Peptide

A short chain of amino acids linked by peptide bonds. Longer chains are called proteins; the boundary is conventional rather than exact.

Agonist

A molecule that binds a receptor and activates it. An antagonist binds and blocks it instead.

GLP-1

Glucagon-like peptide-1, a gut hormone released after eating that influences insulin secretion, gastric emptying and appetite.

GIP

Glucose-dependent insulinotropic polypeptide, the other principal human incretin. Tirzepatide acts on both GIP and GLP-1 receptors.

Incretin

A gut hormone that increases insulin secretion in response to eating. GLP-1 and GIP are the two main ones.

Secretagogue

A substance that causes a gland to secrete something it already produces — as distinct from administering that substance directly.

GHRH

Growth-hormone-releasing hormone, the hypothalamic signal that prompts pituitary growth hormone release. Sermorelin is its active fragment.

Analogue

A molecule structurally modified from a natural one, usually to change stability, half-life or receptor selectivity.

Regulatory and legal

Approved / licensed

Authorised by a regulator for a specific indication after review of safety, efficacy and manufacturing. Carries labelling, pharmacovigilance and legal accountability.

Compounded

Prepared by a pharmacy rather than an original manufacturer, to meet a need an approved product does not. Not FDA-approved and not reviewed the same way. See compounded GLP-1.

Research use only (RUO)

A designation stating a product is not intended for human or veterinary use. It is the legal basis on which most research peptides are sold.

Off-label

Prescribing an approved medicine for a use outside its licensed indication. Legal and common, but a clinical decision made by a prescriber.

Indication

The specific condition and population a medicine is approved to treat. Two products with the same ingredient can have different indications.

Prohibited list

The list of substances and methods banned in tested sport, revised annually by anti-doping authorities. Most compounds on this site appear on it.