GLP-1 Glossary: Key Terms Explained

GLP-1

Glucagon-like peptide-1. A hormone produced in the small intestine after eating. It signals fullness to the brain, slows the rate at which food leaves the stomach (gastric emptying), and helps regulate blood sugar by stimulating insulin release. GLP-1 receptor agonist medications mimic this hormone's effects, amplifying the natural satiety signal. See: What Is a GLP-1? A Plain-English Explainer.

GIP

Glucose-dependent insulinotropic polypeptide. Another incretin hormone, produced in the gut after eating. GIP stimulates insulin secretion and plays a role in fat metabolism and energy storage. Tirzepatide targets both the GIP receptor and the GLP-1 receptor — the dual mechanism is thought to explain its greater average weight loss compared to GLP-1-only drugs.

Incretin

A class of gut hormones — primarily GLP-1 and GIP — released after eating in response to nutrients in the small intestine. Incretins stimulate insulin release from the pancreas in a glucose-dependent way (meaning they only trigger insulin when blood sugar is elevated), which is why GLP-1 medications have a lower risk of causing hypoglycaemia than some older diabetes drugs.

Semaglutide

A GLP-1 receptor agonist medication. Approved as Ozempic (injectable, for type 2 diabetes), Wegovy (injectable, for weight management and MASH with fibrosis), and Rybelsus (oral tablet, for type 2 diabetes). All three contain the same active molecule at different doses and formulations. See: What Is Semaglutide?

Tirzepatide

A dual GIP and GLP-1 receptor agonist. Approved as Mounjaro (for type 2 diabetes) and Zepbound (for weight management and obstructive sleep apnea in adults with obesity). The additional GIP mechanism distinguishes it from semaglutide and is associated with greater average weight loss in head-to-head trials. See: What Is Tirzepatide?

Retatrutide

An investigational triple receptor agonist targeting GLP-1, GIP, and glucagon receptors — a so-called "triple G" mechanism. Phase 3 trials are ongoing; retatrutide is not approved as of 2026. See: Retatrutide vs Ozempic: What to Know.

Cagrilintide

A long-acting amylin analogue (amylin is a hormone co-secreted with insulin that suppresses appetite and slows digestion). Cagrilintide is being developed in combination with semaglutide under the name CagriSema. Not approved as of 2026. See: CagriSema Explained.

Compounded medication

A medication prepared by a licensed pharmacy specifically for an individual patient when a commercially available product doesn't meet their needs — for example, due to an allergy to an inactive ingredient, or a required dose not available commercially. During the 2022–2024 semaglutide shortage, compounding pharmacies could legally prepare compounded semaglutide under a shortage exemption. That exemption ended in February 2025. See: Is Compounded Semaglutide Legal in 2026?

Titration

The process of gradually increasing a medication's dose over a schedule — typically weeks to months — to allow the body to adjust and to minimise side effects. GLP-1 medications are always started at a low dose and titrated upward. The titration schedule is set by the prescribing clinician and should not be accelerated without clinical guidance.

Subcutaneous injection

An injection into the fatty tissue just beneath the skin — not into muscle (intramuscular) and not into a vein (intravenous). Injectable GLP-1 medications like Ozempic, Wegovy, Mounjaro, and Zepbound are all given subcutaneously, typically in the abdomen, thigh, or upper arm, once weekly using a pre-filled auto-injector pen.

MASH

Metabolic dysfunction-associated steatohepatitis. The inflammatory form of fatty liver disease, previously called NASH (non-alcoholic steatohepatitis). MASH can progress to liver fibrosis and cirrhosis. In 2025, semaglutide 2.4mg (Wegovy) received FDA approval specifically for MASH with liver fibrosis, based on the ESSENCE trial. See: GLP-1s and Fatty Liver (MASH).

AHI (Apnea-Hypopnea Index)

The number of breathing interruptions (apneas and hypopneas) per hour of sleep, used to measure the severity of obstructive sleep apnea. Mild OSA is 5–14 events/hour; moderate is 15–30; severe is 30 or more. Tirzepatide (Zepbound) is FDA-approved for moderate-to-severe OSA in adults with obesity. See: GLP-1s and Sleep Apnea.

Telogen effluvium

A form of temporary, diffuse hair shedding triggered by physical or nutritional stress — including rapid weight loss and low protein intake. It typically appears 2–4 months after the stressor and resolves as intake stabilises. It is not caused by the GLP-1 molecule directly. See: GLP-1s and Hair Loss.

BMI (Body Mass Index)

A measure of body weight relative to height (weight in kg divided by height in metres squared). Used as a screening tool for weight-related health risk. GLP-1 medications approved for weight management are generally indicated for adults with a BMI of 30 or above, or 27 or above in the presence of at least one weight-related comorbidity such as type 2 diabetes, hypertension, or dyslipidaemia.