GLP-1 glossary: medical terms in plain English

Medicines and how they work

Active ingredient: the substance in a medicine responsible for its intended effect on the body. Brand name: the commercial name of a particular product. Products with the same ingredient still differ in formulation, strength, device and authorised use.

GLP-1: glucagon-like peptide-1, a hormone involved in the body's response to food. GIP: glucose-dependent insulinotropic polypeptide, another incretin hormone. Receptor agonist: a substance which switches on a receptor. Dual agonist: a medicine acting on two receptor targets. Tirzepatide acts on GIP and GLP-1 receptors.

Formulation: how an ingredient is prepared and delivered, such as a tablet or an injectable solution. Bioavailability: the share of a dose reaching the bloodstream in a usable form. These ideas explain why oral and injectable milligram amounts do not swap directly.

Prescribing and regulation

Indication: the condition and patient group a medicine is authorised for. Marketing authorisation: regulatory permission to supply a named medicine on set terms. A licence does not mean the NHS funds the medicine or that every person suits it.

Off-label: using a licensed medicine outside one of the terms of its authorisation. Unlicensed medicine: a medicine without the relevant marketing authorisation. The two are different. A genuine special clinical need can sometimes justify an unlicensed medicine. Saving money is no such justification.

SmPC: Summary of Product Characteristics, the product information for professionals. PIL: Patient Information Leaflet. Titration: changing a dose step by step to a plan. Maintenance dose: the dose for ongoing treatment after any initial increases, as set by the product or by your prescriber.

Symptoms and safety

Adverse event: something unwanted which happens during treatment, whether or not the treatment caused it. Adverse drug reaction: a harmful, unintended response suspected or shown to be linked to a medicine. A Yellow Card report records a suspicion and does not prove cause on its own.

Hypoglycaemia: low blood glucose. Pancreatitis: inflammation of the pancreas. Aspiration: material entering the airway or lungs, which matters most in talks about anaesthesia. Contraindication: a situation in which the product information says a medicine should not be used.

Research and outcomes

Randomisation: putting study participants into groups by chance. Placebo: a comparison treatment without the active medicine under test. Comparator: the treatment or approach another is measured against. An active comparator contains a real treatment instead of a placebo.

Endpoint: an outcome a study measures. Mean: an arithmetic average, which few people match exactly. Absolute difference: the direct gap between two outcomes. Relative difference: the change expressed against a comparison value. Confidence interval: a statistical range showing the uncertainty around an estimate. These terms help you test a claim, and the study design and population still matter most.

Terms shift meaning between settings

Approved can mean a regulator's authorisation, a clinician's decision to prescribe or an insurer agreeing to pay. Eligible can mean within a product licence or within a narrower funding pathway. Ask what the writer means and which country the statement covers. If a term stays unclear in a consultation, ask for an everyday example. Knowing what a term means for you in practice helps more than memorising the abbreviation, especially when several organisations share your care.