GLP-1 Glossary
Every term you'll encounter in GLP-1 conversations, plainly defined. Bookmark this page — most articles on the site link back here.
GLP-1 medicine is full of abbreviations, hormone names, lab values, and clinic jargon that nobody bothers to translate. This glossary translates them. Terms are grouped alphabetically; clinical numbers are written so they make sense without a textbook nearby. If a term is missing, it usually means it has not come up in patient conversations often enough to need defining — message us and we will add it.
A–C
A1c (HbA1c)
A blood test that reflects your average blood sugar over the past two to three months. Reported as a percentage. Under 5.7% is normal, 5.7 to 6.4% is prediabetes, and 6.5% or higher is diabetes. GLP-1s typically lower A1c by 1 to 2 percentage points.
Agonist
A drug that activates a receptor the way the body's own signaling molecule would. A GLP-1 receptor agonist mimics the gut hormone GLP-1 by binding to and turning on the same receptor.
AHI (Apnea-Hypopnea Index)
The number of breathing pauses per hour of sleep, used to grade obstructive sleep apnea. Tirzepatide (Zepbound) carries an FDA indication for moderate-to-severe OSA in adults with obesity based on AHI reduction in trials.
BMI (Body Mass Index)
Weight in kilograms divided by height in meters squared. A blunt screening number — useful for population-level thresholds but a poor measure of an individual's body composition. Insurance and FDA labels still use it.
BMR (Basal Metabolic Rate)
The calories your body burns at rest to keep basic systems running — breathing, circulation, temperature. Roughly 60 to 70% of total daily energy expenditure.
Compounded GLP-1
A version of semaglutide or tirzepatide mixed by a compounding pharmacy rather than manufactured by Novo Nordisk or Eli Lilly. Legal status has shifted as FDA shortages have resolved. Identity, dosing accuracy, and sterility vary by pharmacy.
D–G
DPP-4
Dipeptidyl peptidase-4, the enzyme that breaks down natural GLP-1 within minutes. Modern GLP-1 drugs are engineered to resist DPP-4, which is why they last a week instead of a few minutes.
eGFR
Estimated glomerular filtration rate, a measure of how well your kidneys filter blood. Reported in mL/min/1.73 m². Above 60 is generally normal. Many providers want a baseline eGFR before starting a GLP-1.
Food noise
The patient-coined term for the constant, intrusive mental chatter about food — thinking about the next meal while finishing the current one. GLP-1s quiet it for most people, and the quiet is often the most surprising effect.
Gastric emptying
The rate at which food leaves the stomach into the small intestine. GLP-1s slow it — which is why small meals feel filling and why fatty or large meals can trigger nausea.
GIP
Glucose-dependent insulinotropic polypeptide, another gut hormone released after eating. Tirzepatide is a dual GIP and GLP-1 agonist; semaglutide hits GLP-1 only. The added GIP activity is one hypothesis for tirzepatide's larger weight effect.
GLP-1
Glucagon-like peptide-1, a hormone secreted by L-cells in the gut after eating. It triggers insulin release, slows gastric emptying, suppresses glucagon, and signals satiety to the brain. The drug class is named after the hormone they mimic.
H–M
Half-life
How long it takes for half the drug to clear from the bloodstream. Semaglutide's half-life is about a week, which is why dosing is once weekly and why a missed dose still leaves plenty of drug on board for a few days.
Hypoglycemia
Low blood sugar. GLP-1s rarely cause hypoglycemia on their own because they only stimulate insulin in response to glucose. Risk rises when stacked with insulin or a sulfonylurea.
Incretin
An umbrella term for gut hormones released after eating that boost insulin secretion. GLP-1 and GIP are the two main human incretins. "Incretin mimetic" is an older name for the GLP-1 drug class.
MACE
Major Adverse Cardiovascular Events — typically defined as cardiovascular death, non-fatal heart attack, and non-fatal stroke. Wegovy carries an FDA indication for reducing MACE in adults with established cardiovascular disease and obesity, based on the SELECT trial.
MEN-2 (Multiple Endocrine Neoplasia type 2)
A rare inherited syndrome that causes medullary thyroid cancer and other tumors. A personal or family history of MEN-2 is a label contraindication for all GLP-1 receptor agonists.
MTC (Medullary Thyroid Carcinoma)
A specific, rare form of thyroid cancer. GLP-1 labels carry a boxed warning because rodent studies showed thyroid C-cell tumors at high doses. Human data has not confirmed an increased risk, but a personal or family history of MTC is a contraindication.
N–Z
NSV (Non-Scale Victory)
A progress marker that has nothing to do with the scale: rings fitting again, walking up stairs without losing breath, fewer migraines, a smaller dose of blood pressure medication. NSVs often precede scale changes and outlast them.
Off-label
A prescription written for a use that is not on the drug's FDA label. Ozempic prescribed for weight loss is the most common GLP-1 off-label example — the drug is approved for type 2 diabetes only.
Pancreatitis
Inflammation of the pancreas. A rare but serious GLP-1 side effect. Signature symptom: severe upper abdominal pain that radiates to the back, usually with vomiting. Stop the drug and seek care immediately if suspected.
Plateau
A stretch of weeks where the scale stops moving despite continued treatment. Real plateaus exist and are biological, not failures. Often they break with a dose increase, a protein audit, or simply more time.
Sarcopenia
Loss of muscle mass and strength. A concern on any rapid-weight-loss regimen, including GLP-1s. Protected by adequate protein intake and resistance training during weight loss.
Sulfur burps
Belches that smell strongly of rotten eggs, caused by hydrogen sulfide gas from slowed gastric emptying. A common, harmless, deeply unpleasant side effect — usually responds to smaller meals and lower-fat choices.
TDEE (Total Daily Energy Expenditure)
The total calories you burn in a day — BMR plus activity plus the thermic effect of food. Used to set a calorie target for weight maintenance or loss.
Telogen effluvium
A reversible form of hair shedding triggered by a metabolic stressor — rapid weight loss being one of them. Typically begins three to four months after the stressor and resolves over six to nine months. Not unique to GLP-1s.
Titration
The scheduled, gradual increase in GLP-1 dose over the first months of treatment. Designed to let the gut adapt — every label requires a starter dose well below the therapeutic dose.
Keep exploring
Most terms here link to deeper articles elsewhere on the site. Start at the Resources hub to browse by topic, or jump to the newcomer guide if you are still in your first weeks.