GLP-1 glossary — every drug, mechanism, metric, and trial term

Drugs

Liraglutide: First-generation GLP-1 receptor agonist; active ingredient in Saxenda and Victoza.
Semaglutide: GLP-1 receptor agonist; active ingredient in Wegovy, Ozempic, and Rybelsus.
Tirzepatide: Dual GIP/GLP-1 receptor agonist; active ingredient in Mounjaro and Zepbound.

Mechanism

GIP: Second gut hormone targeted by tirzepatide (Zepbound, Mounjaro). Dual GIP/GLP-1 action drives stronger weight loss than single-agonist drugs.
GLP-1: Glucagon-like peptide-1 receptor agonist — class of drugs that mimic a gut hormone to reduce appetite and slow stomach emptying.
Incretin: Gut hormone (GLP-1 or GIP) that stimulates insulin secretion in response to oral glucose.

Metrics

A1C: Average blood sugar over the past 2-3 months. Healthy: <5.7%. Pre-diabetes: 5.7-6.4%. Diabetes: ≥6.5%.
BMI: Body mass index = weight (kg) / height (m)². Overweight: 25-29.9. Obese: ≥30. FDA threshold for Wegovy/Zepbound: BMI ≥30, or ≥27 with weight-related condition.

Conditions

Type 2 diabetes: Chronic insulin resistance with relative insulin deficiency. Diagnosis: A1C ≥6.5%.

Clinical trials

SCALE: Pivotal trial of Saxenda (liraglutide 3.0 mg) for chronic weight management.
SELECT trial: Landmark 2023 cardiovascular outcomes study showing semaglutide (Wegovy) cut major cardiovascular events by 20% in adults with prior heart disease.
STEP 1: Pivotal 68-week trial that earned Wegovy its FDA weight-loss approval. Average 14.9% body weight loss vs 2.4% placebo.
SURMOUNT-1: Pivotal 72-week trial behind Zepbound's FDA approval. Average 20.9% body weight loss at the 15 mg dose.
SURPASS-2: Head-to-head trial of Mounjaro (tirzepatide) vs Ozempic (semaglutide) in T2D.
SUSTAIN 6: CV outcomes trial of Ozempic (semaglutide) in T2D. 26% MACE reduction.

Regulatory

Compounded: Non-FDA-approved version mixed by a licensed pharmacy. Cheaper than brand-name but quality varies. Only legal when the FDA declares a drug in shortage.
MTC: Rare thyroid cancer; GLP-1s carry an FDA black-box warning for personal or family history of MTC or MEN 2.
NPI: 10-digit identifier for US healthcare providers, publicly searchable via NPPES Registry.
Prior authorization: Insurance step that requires your doctor to document medical necessity before the plan will cover the drug. Adds 3-14 days but is often required for GLP-1s.

Other terms

Titration: Gradual dose increase over weeks to build tolerance and minimize GI side effects. Typical GLP-1 schedule: 4-week steps up to the maintenance dose.

Mechanism

GIP

Second gut hormone targeted by tirzepatide (Zepbound, Mounjaro). Dual GIP/GLP-1 action drives stronger weight loss than single-agonist drugs.

Also known as: glucose-dependent insulinotropic polypeptide.

GLP-1

Glucagon-like peptide-1 receptor agonist — class of drugs that mimic a gut hormone to reduce appetite and slow stomach emptying.

Also known as: GLP-1 agonist, GLP-1 receptor agonist, GLP-1 RA.

Incretin

Gut hormone (GLP-1 or GIP) that stimulates insulin secretion in response to oral glucose.

Metrics

A1C

Average blood sugar over the past 2-3 months. Healthy: <5.7%. Pre-diabetes: 5.7-6.4%. Diabetes: ≥6.5%.

Also known as: HbA1c, hemoglobin A1C.

BMI

Body mass index = weight (kg) / height (m)². Overweight: 25-29.9. Obese: ≥30. FDA threshold for Wegovy/Zepbound: BMI ≥30, or ≥27 with weight-related condition.

Also known as: body mass index.

Clinical trials

SCALE

Pivotal trial of Saxenda (liraglutide 3.0 mg) for chronic weight management.

SELECT trial

Landmark 2023 cardiovascular outcomes study showing semaglutide (Wegovy) cut major cardiovascular events by 20% in adults with prior heart disease.

STEP 1

Pivotal 68-week trial that earned Wegovy its FDA weight-loss approval. Average 14.9% body weight loss vs 2.4% placebo.

Also known as: STEP 1 trial.

SURMOUNT-1

Pivotal 72-week trial behind Zepbound's FDA approval. Average 20.9% body weight loss at the 15 mg dose.

Also known as: SURMOUNT trial.

SURPASS-2

Head-to-head trial of Mounjaro (tirzepatide) vs Ozempic (semaglutide) in T2D.

SUSTAIN 6

CV outcomes trial of Ozempic (semaglutide) in T2D. 26% MACE reduction.

Regulatory

Compounded

Non-FDA-approved version mixed by a licensed pharmacy. Cheaper than brand-name but quality varies. Only legal when the FDA declares a drug in shortage.

Also known as: compounded semaglutide, compounded tirzepatide.

MTC

Rare thyroid cancer; GLP-1s carry an FDA black-box warning for personal or family history of MTC or MEN 2.

Also known as: medullary thyroid carcinoma.

NPI

10-digit identifier for US healthcare providers, publicly searchable via NPPES Registry.

Also known as: National Provider Identifier.

Prior authorization

Insurance step that requires your doctor to document medical necessity before the plan will cover the drug. Adds 3-14 days but is often required for GLP-1s.

Also known as: PA, prior auth.

Every GLP-1 term, explained

Drugs

Mechanism

Metrics

Conditions

Clinical trials

Regulatory

Other terms

Every GLP-1 term, explained

Drugs

Mechanism

Metrics

Conditions

Clinical trials

Regulatory

Other terms