GLP-1 Glossary: 56 Terms Defined

5

503A pharmacy

A traditional compounding pharmacy operating under section 503A of the Federal Food, Drug, and Cosmetic Act. 503A pharmacies prepare compounded medications for individually identified patients based on a valid prescription. They are regulated primarily by state boards of pharmacy and must comply with USP General Chapters including <797> for sterile preparations.

503B outsourcing facility

A pharmaceutical compounding facility registered with the FDA under section 503B of the FD&C Act. Unlike 503A pharmacies, 503B facilities can prepare compounded medications in bulk without patient-specific prescriptions and operate under current Good Manufacturing Practices (cGMP).

A

AGI (active glucagon-like peptide)

The biologically active form of GLP-1. Native GLP-1 has a half-life of about 2 minutes due to rapid degradation by the enzyme DPP-4. Synthetic GLP-1 receptor agonists like semaglutide are engineered to resist DPP-4 degradation.

B

Bremelanotide

Generic name for PT-141, a melanocortin receptor agonist used for hypoactive sexual desire disorder (HSDD) in women. Sold under the brand name Vyleesi.

BMI (body mass index)

Weight in kilograms divided by height in meters squared. Used as a screening tool for weight category. FDA labeling for Wegovy and Zepbound requires BMI ≥30, or BMI ≥27 with at least one weight-related comorbidity.

Boxed warning

The FDA's most serious medication warning, formerly called a 'black box warning,' applied when there is reasonable evidence of a serious hazard with a drug. GLP-1 receptor agonists carry a boxed warning regarding thyroid C-cell tumors based on rodent studies.

C

cGMP (current Good Manufacturing Practice)

FDA regulations governing pharmaceutical manufacturing. 503B outsourcing facilities operate under cGMP; 503A pharmacies do not but must comply with USP standards.

Compounded medication

A medication prepared by a licensed pharmacist for a specific patient. Compounded preparations are not FDA-approved as finished drugs but the active ingredients used must be FDA-approved or otherwise permitted under FDA compounding policy.

D

DPP-4 inhibitor

A class of oral diabetes medication that inhibits the enzyme dipeptidyl peptidase-4, prolonging the action of endogenous GLP-1. Includes sitagliptin (Januvia), linagliptin (Tradjenta), and saxagliptin (Onglyza).

Dual GIP/GLP-1 receptor agonist

A medication that activates both the GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptors. Tirzepatide is the only FDA-approved dual GIP/GLP-1 agonist.

E

Endotoxin

A toxin associated with the cell wall of Gram-negative bacteria. USP <85> Bacterial Endotoxins Test is the standard for endotoxin testing in injectable preparations.

F

FDA Drug Shortage List

The FDA's official registry of drugs in shortage. Compounded versions of FDA-approved drugs may be prepared under section 503A while the brand-name product is on this list, subject to additional conditions.

Flat-rate pricing

A pricing model in which the patient pays the same monthly amount regardless of dose. Contrasts with tiered titration pricing, in which monthly cost increases as the patient titrates to higher doses.

Foundayo (orforglipron)

An oral GLP-1 receptor agonist approved by the FDA in 2026. Manufactured by Eli Lilly. The first oral GLP-1 with weight-loss efficacy approaching injectable agents.

G

Generic drug

A pharmaceutical product approved under an Abbreviated New Drug Application (ANDA) that is bioequivalent to the reference listed drug. There is no FDA-approved generic version of semaglutide, tirzepatide, or any branded GLP-1 as of May 2026.

GHK-Cu

Copper tripeptide-1, a small peptide combining glycine, histidine, lysine, and copper. Studied for tissue repair, wound healing, and skin barrier function.

GIP (glucose-dependent insulinotropic polypeptide)

An incretin hormone secreted by K-cells in the duodenum and jejunum. Stimulates insulin secretion in response to glucose. The GIP receptor is the second target of tirzepatide.

GLP-1 (glucagon-like peptide-1)

An incretin hormone secreted by L-cells in the ileum and colon in response to nutrient intake. Stimulates glucose-dependent insulin secretion, suppresses glucagon release, slows gastric emptying, and promotes satiety.

GLP-1 receptor agonist (GLP-1 RA)

A class of medication that activates the GLP-1 receptor. Includes semaglutide (Ozempic, Wegovy, Rybelsus), liraglutide (Victoza, Saxenda), dulaglutide (Trulicity), exenatide (Byetta, Bydureon), and others.

H

HSA/FSA

Health Savings Account (HSA) and Flexible Spending Account (FSA). Tax-advantaged accounts that can typically be used to pay for FDA-approved medications. Compounded medications' HSA/FSA eligibility varies by plan administrator.

I

Incretin

A hormone secreted by the gut in response to nutrient intake that stimulates insulin secretion. The two main incretins in humans are GLP-1 and GIP.

Indication

The medical condition or use for which a drug has been approved by the FDA. Off-label use refers to prescribing a drug for an indication not on its FDA-approved label.

Injection site reaction

Localized redness, swelling, itching, or bruising at the site of injection. Common with subcutaneous GLP-1 administration; typically transient and self-resolving.

L

LegitScript certification

A third-party certification program for online pharmacies and telemedicine services. Certified providers meet LegitScript's standards for legal compliance, transparency, and patient safety.

Liraglutide

A GLP-1 receptor agonist with a 13-hour half-life requiring daily injection. Sold as Victoza (for type 2 diabetes) and Saxenda (for chronic weight management). Manufacturer: Novo Nordisk.

M

MASH (metabolic dysfunction-associated steatohepatitis)

Formerly NASH. Liver inflammation and damage caused by fat accumulation in the liver in patients with metabolic syndrome. GLP-1 RAs are under active study for MASH treatment.

Medical necessity

Documentation by a prescribing clinician that a medication is required for the individual patient's clinical care. Required for compounded GLP-1 prescribing under FDA's 2025 enforcement framework.

Methylcobalamin

The active form of vitamin B12. Frequently included in compounded GLP-1 formulations to mitigate fatigue and support energy metabolism during titration.

MTC (medullary thyroid carcinoma)

A rare thyroid cancer. GLP-1 RAs are contraindicated in patients with a personal or family history of MTC or with multiple endocrine neoplasia syndrome type 2 (MEN 2).

Mounjaro

Brand name for tirzepatide approved by the FDA in May 2022 for type 2 diabetes. Manufacturer: Eli Lilly.

N

NAFLD (non-alcoholic fatty liver disease)

Fat accumulation in the liver not caused by alcohol. Now often called metabolic dysfunction-associated steatotic liver disease (MASLD). Strongly associated with obesity and insulin resistance.

O

Off-label use

Prescribing a drug for an indication, dose, route, or patient population not included in its FDA-approved labeling. Legal in the U.S. but the prescribing clinician must document medical necessity.

Orange Book

The FDA's 'Approved Drug Products with Therapeutic Equivalence Evaluations,' the official source of FDA-approved drugs.

Orforglipron

An oral, non-peptide GLP-1 receptor agonist approved by the FDA in 2026 under the brand name Foundayo. Manufactured by Eli Lilly. Unlike Rybelsus, orforglipron does not require fasting for absorption.

Ozempic

Brand name for semaglutide approved by the FDA in December 2017 for type 2 diabetes. Dosed once weekly. Manufacturer: Novo Nordisk.

P

Pancreatitis

Inflammation of the pancreas. A rare but serious potential adverse event with GLP-1 RAs; patients with a history of pancreatitis are not typically candidates for GLP-1 therapy.

Pen injector

A pre-filled, multi-dose injection device used to administer subcutaneous GLP-1 medications. Ozempic, Wegovy, Mounjaro, and Zepbound are supplied in pen injectors.

Prior authorization (PA)

A coverage requirement imposed by an insurance carrier in which the prescribing clinician must document clinical criteria before the insurer will pay for a medication. Wegovy and Zepbound typically require PA.

PT-141

Bremelanotide. See entry above.

R

Rybelsus

Brand name for oral semaglutide tablets approved by the FDA in September 2019 for type 2 diabetes. Requires fasting administration. Manufacturer: Novo Nordisk.

S

Saxenda

Brand name for liraglutide approved by the FDA in December 2014 for chronic weight management. Dosed once daily. Manufacturer: Novo Nordisk.

Semaglutide

A GLP-1 receptor agonist with a ~1-week half-life enabling once-weekly dosing. Sold as Ozempic (type 2 diabetes), Wegovy (chronic weight management), and Rybelsus (oral, type 2 diabetes). Manufacturer: Novo Nordisk.

Sermorelin

A growth hormone-releasing hormone (GHRH) analog used in compounded preparations to stimulate endogenous growth hormone secretion.

Subcutaneous (SC, SQ)

Beneath the skin. Subcutaneous injection is the standard route of administration for injectable GLP-1 RAs. Common sites: abdomen, thigh, upper arm.

Sublingual

Under the tongue. Some compounded GLP-1 preparations are marketed for sublingual administration; bioavailability of sublingual GLP-1 is not well-characterized in peer-reviewed literature.

T

Tachyphylaxis

Decreasing response to a drug despite continued administration. Not a recognized phenomenon with GLP-1 RAs at standard doses.

Telehealth

The delivery of health services by remote means using telecommunications technology. Telehealth prescribing for GLP-1 medications is permitted in all 50 U.S. states under varying state-specific rules.

Tesamorelin

A growth hormone-releasing hormone analog FDA-approved for HIV-associated lipodystrophy. Sometimes used off-label or in compounded preparations for abdominal fat reduction.

Tirzepatide

A dual GIP/GLP-1 receptor agonist with a ~5-day half-life enabling once-weekly dosing. Sold as Mounjaro (type 2 diabetes), Zepbound (chronic weight management; obstructive sleep apnea). Manufacturer: Eli Lilly.

Titration

Gradual dose escalation. GLP-1 RAs are typically titrated up over 12-20 weeks to improve gastrointestinal tolerance.

U

USP <85>

United States Pharmacopeia General Chapter 85: Bacterial Endotoxins Test. The reference standard for endotoxin testing in injectable preparations.

USP <797>

United States Pharmacopeia General Chapter 797: Pharmaceutical Compounding — Sterile Preparations. The reference standard for the preparation of sterile compounded medications.

USP <800>

United States Pharmacopeia General Chapter 800: Hazardous Drugs — Handling in Healthcare Settings.

V

Victoza

Brand name for liraglutide approved by the FDA in January 2010 for type 2 diabetes. Dosed once daily. Manufacturer: Novo Nordisk.

W

Wegovy

Brand name for high-dose semaglutide approved by the FDA in June 2021 for chronic weight management. Dosed once weekly with titration to 2.4 mg. Manufacturer: Novo Nordisk.

Z

Zepbound

Brand name for tirzepatide approved by the FDA in November 2023 for chronic weight management. Also FDA-approved in December 2024 for moderate-to-severe obstructive sleep apnea in adults with obesity. Manufacturer: Eli Lilly.

Missing a term?

The glossary is a living document. If you encounter a term in our coverage that isn't defined here, email glpagonists@gmail.com and we'll add it.