Reference

The glossary.

Name: GLP-1 Glossary
Published: 2026-01-12

Fifty-plus defined terms across regulatory, pharmacology, clinical, trial, and rubric vocabularies. Linked across the site.

Regulatory

503A pharmacy: A pharmacy that prepares patient-specific compounded medications under state pharmacy-board licensure. 503A pharmacies derive their authority from section 503A of the Federal Food, Drug, and Cosmetic Act. Each prescription is individualized to a specific patient; batched preparation is not permitted under this pathway.
503B Bulks List: FDA's list of bulk drug substances that 503B FDA-registered outsourcing facilities may use as starting materials in compounded preparations. A substance must either be on the Bulks List or have a documented clinical need to be compounded from bulk for a specific patient.
503B outsourcing facility: An FDA-registered facility that can prepare batches of compounded medications without patient-specific prescriptions, operating under cGMP-equivalent standards. 503B facilities are subject to FDA inspection and are governed by section 503B of the Federal Food, Drug, and Cosmetic Act.
Certificate of Analysis (CoA): A per-batch document showing the quality testing performed on a specific lot of a compounded preparation. Typically includes sterility (USP <71>), bacterial endotoxin (USP <85>), and potency (HPLC) results. CoA-on-request availability is a positive disclosure signal for compounding pharmacies.
cGMP (current Good Manufacturing Practice): The FDA's quality framework for drug manufacturing facilities, defining the procedures, controls, and documentation required to produce drugs of consistent identity, strength, and quality. 503B outsourcing facilities operate under cGMP-equivalent standards.
Compounding: The pharmacy preparation of a customized medication for a specific patient, or batched preparation by an FDA-registered outsourcing facility. Compounded preparations are not FDA-approved drug products, even when they contain the same active pharmaceutical ingredient as a brand-name drug.
FDA approval: Authorization from the US Food and Drug Administration to market a drug for a specific indication, based on demonstrated safety and efficacy. Compounded preparations are not FDA-approved drug products even when they contain the same active ingredient as an approved drug.
FDA Drug Shortages list: FDA's official list of drugs currently in shortage. Listing creates limited exceptions allowing compounding pharmacies to prepare otherwise-restricted drug products to maintain patient access. Semaglutide and tirzepatide were both removed from the list in 2024–2025.
HPLC potency testing: High-performance liquid chromatography testing for the concentration of the active pharmaceutical ingredient in a compounded preparation. Typically performed on a per-batch basis and reported on the certificate of analysis.
LegitScript: A third-party certification organization for online pharmacies and telehealth providers. LegitScript-verified status is a meaningful but not exhaustive signal of regulatory and operational compliance.
PCAB accreditation: Pharmacy Compounding Accreditation Board — a third-party certification for compounding pharmacies compliant with USP <797> sterile-compounding and related standards. A meaningful disclosure signal.
USP <71> Sterility Testing: United States Pharmacopeia chapter governing sterility testing of compounded sterile preparations. Required on a per-batch basis for injectable compounded medications.
USP <797> Sterile Compounding: USP chapter governing sterile compounding practices, including environmental controls, beyond-use dating, and personnel competency. The foundational standard for 503A sterile compounding pharmacies.
USP <800> Hazardous Drugs: USP chapter governing handling of hazardous drugs in healthcare settings to minimize occupational exposure. Relevant to compounding facilities handling oncology and selected other agents.
USP <85> Bacterial Endotoxins Test: USP chapter governing bacterial-endotoxin testing of compounded sterile preparations. Endotoxins are pyrogenic substances from gram-negative bacterial cell walls; their detection above threshold disqualifies a batch from release.

Pharmacology

DPP-4 inhibitor: Dipeptidyl peptidase-4 inhibitor — an oral medication class for type 2 diabetes that works by slowing the degradation of endogenous GLP-1 and GIP. DPP-4 inhibitors (e.g., sitagliptin) produce smaller glucose and weight effects than GLP-1 receptor agonists.
Glucagon-like peptide-1 (GLP-1): An incretin hormone secreted by intestinal L-cells that enhances glucose-dependent insulin secretion, slows gastric emptying, and reduces appetite. Synthetic GLP-1 receptor agonists (semaglutide, liraglutide, dulaglutide, exenatide) are the foundational class of GLP-1 therapy.
Glucose-dependent insulinotropic polypeptide (GIP): An incretin hormone secreted by intestinal K-cells in response to food intake. GIP enhances glucose-dependent insulin secretion. Tirzepatide is the first approved drug agonizing both GIP and GLP-1 receptors.
Incretin: A gut hormone secreted in response to food intake that enhances insulin secretion. The two main incretins are GLP-1 and GIP. Incretin-based therapies include GLP-1 receptor agonists, dual GLP-1/GIP agonists, and DPP-4 inhibitors.
LillyDirect: Eli Lilly's direct-to-consumer pharmacy program offering reduced cash-pay pricing on selected products, including tirzepatide single-dose vials. Sits between brand-name list pricing and compounded telehealth pricing.
Liraglutide: A once-daily GLP-1 receptor agonist (Saxenda for obesity at 3.0 mg, Victoza for T2D at 1.2/1.8 mg). The first GLP-1 receptor agonist approved for chronic weight management (2014). Largely superseded by once-weekly semaglutide and tirzepatide.
Mechanism of action (MoA): The specific biochemical pathway by which a drug produces its effect. The MoA of GLP-1 receptor agonists includes glucose-dependent insulin secretion, slowed gastric emptying, and central appetite suppression.
Mounjaro: Brand name for tirzepatide as approved by FDA for the treatment of type 2 diabetes. Manufactured by Eli Lilly. The same molecule is marketed as Zepbound for chronic weight management and OSA.
Ozempic: Brand name for semaglutide as approved for type 2 diabetes. Manufactured by Novo Nordisk. The same molecule is marketed as Wegovy for chronic weight management at higher dose, and as Rybelsus in oral formulation.
Retatrutide: Eli Lilly's investigational triple agonist of GLP-1, GIP, and glucagon receptors. Phase-3 obesity trials reported mean weight loss of 22–24% at the 12 mg dose. Not yet FDA-approved; submission anticipated late 2026.
Rybelsus: Brand name for oral semaglutide for type 2 diabetes. Manufactured by Novo Nordisk. The only oral GLP-1 receptor agonist currently FDA-approved.
Saxenda: Brand name for liraglutide 3.0 mg as approved for chronic weight management. Manufactured by Novo Nordisk. The first GLP-1 receptor agonist approved for obesity (2014).
Semaglutide: A long-acting GLP-1 receptor agonist, the active ingredient in Ozempic (T2D), Wegovy (obesity, CV risk), and Rybelsus (oral, T2D). Manufactured by Novo Nordisk. Originally approved in 2017.
Tirzepatide: A long-acting dual agonist of GLP-1 and GIP receptors, the active ingredient in Mounjaro (T2D), Zepbound (obesity, OSA). Manufactured by Eli Lilly. Originally approved in 2022.
Wegovy: Brand name for semaglutide 2.4 mg as approved for chronic weight management and (since 2024) for cardiovascular risk reduction in adults with overweight/obesity and established CVD. Manufactured by Novo Nordisk.
Zepbound: Brand name for tirzepatide as approved for chronic weight management and (since December 2024) for moderate-to-severe obstructive sleep apnea in adults with obesity. Manufactured by Eli Lilly.

Clinical

Apnea–hypopnea index (AHI): The number of apnea and hypopnea events per hour of sleep. Used to grade obstructive sleep apnea severity: AHI 5–14 mild, 15–29 moderate, ≥30 severe. AHI <5 is the typical clinical-remission threshold.
Body mass index (BMI): A weight-for-height index calculated as weight in kilograms divided by the square of height in meters. Used as a population-level screening tool for underweight, normal weight, overweight, and obesity. BMI ≥ 30 is the standard obesity threshold; BMI ≥ 27 with a weight-related comorbidity qualifies for most FDA-approved weight-loss medications.
HbA1c (glycated hemoglobin): A measure of average blood glucose over the prior 2–3 months, expressed as a percentage. Normal < 5.7%; prediabetes 5.7–6.4%; diabetes ≥ 6.5%. The primary glycemic outcome in T2D trials.
MASH (metabolic dysfunction-associated steatohepatitis): A progressive form of fatty liver disease with hepatocyte injury, inflammation, and risk of fibrosis and cirrhosis. Formerly NASH. GLP-1 therapies show promise on MASH histology in phase-2 trials but are not yet FDA-approved for the indication.
Medullary thyroid carcinoma (MTC): A rare form of thyroid cancer arising from parafollicular C-cells. Personal or family history of MTC is a contraindication to GLP-1 receptor agonists based on observations in rodent studies, though the human relevance is uncertain.
Multiple Endocrine Neoplasia syndrome type 2 (MEN 2): A hereditary cancer syndrome that includes medullary thyroid carcinoma. A contraindication to GLP-1 receptor agonists.
NASH (non-alcoholic steatohepatitis): Former name for MASH. The terminology was updated in 2023 to better reflect the metabolic etiology and to avoid the stigmatizing implication of the older 'non-alcoholic' framing.
Obstructive sleep apnea (OSA): A condition characterized by repeated upper-airway collapse during sleep, producing apneas and hypopneas. Severity graded by AHI. Tirzepatide became the first medication FDA-approved for moderate-to-severe OSA in adults with obesity in December 2024.
Polycystic ovary syndrome (PCOS): A common endocrine disorder characterized by ovulatory dysfunction, hyperandrogenism, and polycystic ovarian morphology. Often coexists with insulin resistance and obesity. GLP-1 therapies are used off-label in PCOS for weight and metabolic management.

Trial

SELECT trial: Cardiovascular outcomes trial of semaglutide 2.4 mg in 17,604 adults with overweight/obesity and established CVD, no diabetes. Established a 20% MACE reduction with semaglutide; led to FDA label expansion for CV risk reduction (2024).
STEP trials: Semaglutide Treatment Effect in People with obesity — the pivotal phase-3 program for semaglutide 2.4 mg in obesity. STEP-1 (NEJM 2021) established 14.9% mean weight loss over 68 weeks.
SURMOUNT trials: Pivotal phase-3 trial program for tirzepatide in obesity (SURMOUNT-1 through SURMOUNT-4) and obstructive sleep apnea (SURMOUNT-OSA). SURMOUNT-1 established 22.5% mean weight loss at the 15 mg dose.
SURPASS trials: Pivotal phase-3 trial program for tirzepatide in type 2 diabetes (SURPASS-1 through SURPASS-5). SURPASS-2 (NEJM 2021) established head-to-head superiority over semaglutide 1 mg.
SUSTAIN trials: Pivotal phase-3 trial program for semaglutide in type 2 diabetes (SUSTAIN-1 through SUSTAIN-10). SUSTAIN-6 (NEJM 2016) established CV risk reduction in T2D at high CV risk.

Rubric

Clinical Protocol pillar: 20 points of 100. Evaluates whether a verifiable, named MD/DO directs clinical practice, individualized prescribing protocols, and documented clinical-oversight structure.
Lab Integration & Follow-up pillar: 15 points of 100. Evaluates Quest/LabCorp integration, baseline lab panel completeness, and the documented cadence of clinician check-ins at 4, 12, 26, and 52 weeks.
Outcomes pillar: 20 points of 100. Evaluates published cohort outcomes, transparent adverse-event reporting, and documented discontinuation rates. Most providers score 12–17 due to industry-wide absence of published data.
Pharmacy Traceability pillar: 20 points of 100. Evaluates named pharmacy-partner disclosure, 503A or 503B pathway specification, USP testing practices, and CoA-on-request availability.
Pricing Transparency pillar: 15 points of 100. Evaluates whether monthly pricing is flat across the full titration ladder or stepped, with no hidden dose-based upcharges or contingent fees.
Regulatory Clarity pillar: 10 points of 100. Evaluates whether the provider clearly distinguishes compounded preparations from FDA-approved drug products, accurate description of 503A vs 503B pathway, and active tracking of FDA shortage and Bulks-List status.
Transparency-compliant: Designation under our v3.0 rubric for a provider that clears 70% of each of the six transparency pillars. Under the current rubric, only one provider in the 2026 ranking — NexLife — qualifies.
v3.0 rubric: GLP Review's current scoring framework for provider transparency. 100 points across six pillars; 70% per-pillar pass threshold for transparency-compliant designation. Updated from v2.0 in February 2026.