Reference · not medical advice

Glossary

The vocabulary that shows up on vials, syringes and forums — defined once, plainly.

GLP-1

Glucagon-like peptide-1: a hormone the gut releases after eating. It prompts insulin release, slows stomach emptying and reduces appetite. Semaglutide and liraglutide are GLP-1 analogues.

GLP-2

A real hormone from the same proglucagon precursor as GLP-1, involved in maintaining the gut lining. Unrelated to weight medication, despite vendors using the name as a product tier.

“GLP-3”

Not a hormone. Informal shorthand for retatrutide, a triple agonist.

GIP

Glucose-dependent insulinotropic polypeptide: the other main incretin hormone. Tirzepatide activates the GIP receptor as well as GLP-1's.

Incretin

The family of gut hormones — GLP-1 and GIP — that signal the pancreas after a meal.

Agonist

A molecule that binds a receptor and switches it on, mimicking the natural hormone.

Dual / triple agonist

One molecule that activates two or three different receptors. Tirzepatide is dual (GIP + GLP-1); retatrutide is triple (GIP + GLP-1 + glucagon).

Amylin analogue

A different hormone axis again — cagrilintide is the example — usually paired with a GLP-1 rather than replacing it.

INN

International Non-proprietary Name: the generic molecule name (semaglutide) as opposed to the brand name (Ozempic, Wegovy).

Reconstitution

Adding liquid to a freeze-dried powder to make an injectable solution.

Bacteriostatic water

Sterile water containing 0.9% benzyl alcohol as a preservative, which is what allows a multi-dose vial to be entered more than once.

Concentration (mg/mL)

How much drug sits in each millilitre: vial strength divided by the water added. It is the number that turns a volume into a dose.

Unit (U-100 syringe)

A volume mark, not an amount of drug. On the standard U-100 syringe, 100 units = 1 mL. What a unit is worth in mg depends entirely on the concentration.

Half-life

How long blood levels take to fall by half. It sets how often a drug is dosed and how long it lingers after the last one.

tₘₐₓ

Time from injection to peak blood concentration.

Titration

Stepping a dose up over weeks, following the schedule printed in the product's own label.

Compounded

Prepared by a pharmacy rather than the original manufacturer. In the US this is a regulated channel, separate from the approved pen products.

Definitions only — not medical advice, and never a recommendation about your medication or dose.

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