GLP-1 glossary.
Plain-English definitions of the terms you'll run into on prescriptions, insurance forms, telehealth intake, and clinical trials. Updated as the field evolves.
A
- Anti-obesity medication (AOM)
- An FDA-approved medication used to treat obesity as a chronic disease. The modern AOM class is dominated by GLP-1 and dual GLP-1/GIP agonists (e.g., Wegovy, Zepbound) but also includes older agents like phentermine/topiramate.
B
- BMI (Body Mass Index)
- A weight-to-height ratio used to classify underweight, normal weight, overweight, and obesity. A BMI of 30+ generally defines obesity; 27+ with a weight-related comorbidity often qualifies patients for GLP-1 therapy. BMI calculator →
C
- Compounded GLP-1
- A semaglutide or tirzepatide preparation made by a compounding pharmacy rather than the brand manufacturer. Not FDA-approved for safety, efficacy, or purity. Legality depends on current FDA shortage determinations and the compounding pharmacy's 503A/503B authorization.
D
- Dual agonist
- A drug that activates two receptors simultaneously. Tirzepatide is a dual agonist at the GLP-1 and GIP receptors, which is thought to account for its greater weight-loss efficacy compared to single-agonist GLP-1s.
F
- FDA-approved indication
- The specific medical condition a drug is FDA-approved to treat, as listed on its labeling. The same molecule can have different approved indications under different brand names — e.g., tirzepatide is Mounjaro for diabetes and Zepbound for obesity. Mounjaro vs Zepbound →
- Formulary
- The list of medications your insurance plan will cover, typically organized into tiers that determine your copay. Whether a GLP-1 is on your formulary — and at which tier — largely determines what you'll pay.
G
- GIP (glucose-dependent insulinotropic polypeptide)
- A gut hormone released after meals that stimulates insulin secretion. Tirzepatide activates the GIP receptor in addition to the GLP-1 receptor, producing greater effects on weight and blood sugar than GLP-1 agonism alone.
- GLP-1 (glucagon-like peptide-1)
- A gut hormone that regulates insulin release, slows stomach emptying, and reduces appetite. Synthetic GLP-1 receptor agonists (Ozempic, Wegovy, Saxenda, etc.) leverage this pathway to treat type 2 diabetes and obesity.
- Gastric emptying
- The rate at which food leaves your stomach for the small intestine. GLP-1 drugs slow gastric emptying, which contributes to reduced appetite and caloric intake but can also cause nausea and reflux.
H
- Half-life
- The time it takes for the blood concentration of a drug to fall by half. Semaglutide has a ~7-day half-life and tirzepatide a ~5-day half-life, which is why these drugs are dosed weekly.
I
- Injectable GLP-1
- A GLP-1 medication delivered by subcutaneous injection, usually once weekly via a pre-filled pen or vial-and-syringe. Wegovy, Ozempic, Zepbound, Mounjaro, and Saxenda are injectables. How to inject →
L
- Lean mass
- All body tissue that is not fat — muscle, organs, bone, water, and connective tissue. Rapid weight loss of any kind (GLP-1, surgery, very-low-calorie diet) tends to drive 25-40% lean mass loss unless deliberately mitigated by protein and resistance training. Preserving muscle →
- LillyDirect
- Eli Lilly's direct-to-consumer channel for self-pay patients. Offers Zepbound at a discounted cash price (single-dose vials) through a partner telehealth network. LillyDirect vs NovoCare →
M
- Maintenance dose
- The lowest ongoing dose that holds a patient's weight loss once they have reached their goal. An increasingly common approach rather than fully stopping therapy, as discontinuation typically leads to substantial regain.
- MTC (medullary thyroid carcinoma)
- A rare thyroid cancer that forms the basis of the boxed warning on all GLP-1 drugs, originating from rodent studies. No causal link has been established in humans. Personal or family history of MTC or MEN 2 is a contraindication to GLP-1 therapy.
- Mounjaro
- Brand name for tirzepatide when prescribed for type 2 diabetes. Manufactured by Eli Lilly. The same molecule is sold as Zepbound for chronic weight management.
N
- NovoCare
- Novo Nordisk's direct-to-consumer program for self-pay patients, offering Wegovy at a discounted cash price through partner telehealth providers.
O
- Off-label use
- Prescribing a medication for an indication other than those on its FDA-approved label. Ozempic prescribed for weight loss (rather than type 2 diabetes) is the most common off-label use in the GLP-1 class.
- Orforglipron
- Eli Lilly's oral, non-peptide GLP-1 receptor agonist. Approved by the FDA in 2026. Notable for being the first oral GLP-1 that can be taken without the strict food and water restrictions of Rybelsus. Orforglipron explained →
- Ozempic
- Brand name for injectable semaglutide when prescribed for type 2 diabetes. Manufactured by Novo Nordisk. The same molecule at higher doses is sold as Wegovy for weight management.
P
- Pen (auto-injector)
- A pre-filled, disposable injector used to administer GLP-1 doses subcutaneously. Each pen typically delivers one or more pre-set doses and includes a hidden needle that retracts after use.
R
- Retatrutide
- Eli Lilly's investigational triple agonist (GLP-1 + GIP + glucagon). In Phase 3 trials it has produced the largest weight-loss numbers seen in the class to date. Not yet FDA-approved. Retatrutide explained →
- Rybelsus
- Oral semaglutide approved for type 2 diabetes, manufactured by Novo Nordisk. Must be taken on an empty stomach with strict water and food restrictions to be absorbed effectively.
S
- Saxenda
- Brand name for liraglutide for weight management. A once-daily injectable GLP-1. Generally produces smaller weight loss than weekly semaglutide or tirzepatide.
- Semaglutide
- A once-weekly GLP-1 receptor agonist. Sold as Ozempic for diabetes, Wegovy for weight management, and Rybelsus as an oral tablet. Novo Nordisk is the manufacturer.
- STEP trials
- Novo Nordisk's clinical trial program evaluating semaglutide for weight management. STEP-1 through STEP-8 establish the efficacy and safety basis for Wegovy's FDA approval.
- SURMOUNT trials
- Eli Lilly's clinical trial program evaluating tirzepatide for chronic weight management and its complications (sleep apnea, heart failure, etc.). The basis for Zepbound's FDA approval.
T
- Telehealth program
- A direct-to-consumer service that connects patients with licensed prescribers online and arranges medication fulfillment, often on a monthly subscription. Major GLP-1 telehealth programs include Mochi, Form Health, Hims, PlushCare, and the manufacturer direct programs. Program comparison →
- Telogen effluvium
- A temporary hair-shedding condition triggered by major physiological stress, including rapid weight loss. It typically begins 2-4 months after the trigger and resolves over 6-12 months as the underlying stressor is removed. GLP-1 and hair loss →
- Tirzepatide
- A once-weekly dual GLP-1 / GIP receptor agonist. Sold as Mounjaro for type 2 diabetes and Zepbound for chronic weight management. Eli Lilly is the manufacturer.
- Titration
- The gradual dose escalation used to introduce a GLP-1 to the body and minimize gastrointestinal side effects. Most GLP-1s begin at a non-therapeutic starting dose and increase monthly until the maintenance dose is reached. Dose timeline →
W
- Wegovy
- Brand name for injectable semaglutide (2.4 mg weekly) approved for chronic weight management in adults with obesity or overweight with a comorbidity. Manufactured by Novo Nordisk.
Z
- Zepbound
- Brand name for tirzepatide approved for chronic weight management and obstructive sleep apnea in adults with obesity. Manufactured by Eli Lilly. Same molecule as Mounjaro.
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