GLP-1 Glossary
Plain-English definitions for 51 terms — drugs, trials, mechanisms, side effects, pharmacy concepts, and dosing. Each entry links to the Weight Loss Rankings article that carries the verified primary-source evidence.
This glossary is part of Weight Loss Rankings' living editorial database — 100+ research articles and 158+ clinically-reviewed GLP-1 telehealth providers, sourced only from primary FDA labels and peer-reviewed PubMed literature.
Drugs and brands
FDA-approved GLP-1 medications and their generic active ingredients.
- Wegovy
Once-weekly injectable semaglutide approved by the FDA in 2021 for chronic weight management. Same active ingredient as Ozempic but at higher doses (0.25 to 2.4 mg weekly).
- Ozempic
Once-weekly injectable semaglutide FDA-approved for type 2 diabetes (0.5, 1, 2 mg). Same molecule as Wegovy but lower target doses; commonly prescribed off-label for weight loss.
- Rybelsus
Oral semaglutide tablets (3, 7, 14 mg daily) FDA-approved for type 2 diabetes. The pivotal pharmacokinetic source for the 33% levothyroxine AUC interaction warning.
- Saxenda
Once-daily injectable liraglutide 3.0 mg, FDA-approved 2014 for chronic weight management. Shorter half-life (~13 hours) than the once-weekly GLP-1s requires daily dosing.
- Zepbound
Once-weekly injectable tirzepatide FDA-approved 2023 for chronic weight management. Dual GLP-1/GIP receptor agonist; produced ~21% body weight reduction at 15 mg in SURMOUNT-1.
- Mounjaro
Once-weekly injectable tirzepatide FDA-approved 2022 for type 2 diabetes. Same molecule as Zepbound. Carries the same 4-week backup-contraception warning on oral hormonal contraceptives.
- Foundayo
Orforglipron tablets, the first oral non-peptide GLP-1 receptor agonist, FDA-approved April 2026 by Eli Lilly. Daily oral dosing on empty stomach with a 30-minute fast window.
- Semaglutide
Generic name for the active ingredient in Wegovy, Ozempic, and Rybelsus. GLP-1 receptor agonist with ~7-day half-life enabling once-weekly subcutaneous dosing.
- Tirzepatide
Generic name for the active ingredient in Mounjaro and Zepbound. Dual GLP-1 and GIP receptor agonist with ~5-day half-life. The only injectable GLP-1 with an FDA-mandated oral contraceptive interaction warning.
- Orforglipron
Generic name for Foundayo. The first oral non-peptide GLP-1 receptor agonist. Different mechanism for the oral-contraceptive warning (co-localization in the GI tract) vs tirzepatide's gastric-emptying delay.
- Retatrutide
Eli Lilly's investigational triple agonist (LY3437943) targeting GLP-1, GIP, and glucagon receptors. Phase 2 (NEJM 2023, Jastreboff et al.) showed up to 24.2% body weight reduction at 48 weeks at the highest dose. The first phase 3 readout, TRIUMPH-4 (Dec 2025), reported 28.7% mean weight loss in adults with obesity and knee osteoarthritis. Not yet FDA-approved.
View term page →Retatrutide: Lilly's triple agonist evidence →
- CagriSema
Novo Nordisk's investigational fixed-dose combination of cagrilintide (long-acting amylin analog) plus semaglutide (GLP-1 agonist). REDEFINE 1 reported 20.4% mean weight loss at 68 weeks (22.7% adherent estimand) versus 14.9% with semaglutide alone. Novo has filed an NDA. The result missed Novo's 25% guidance benchmark but still beat semaglutide monotherapy.
- Cagrilintide
Novo Nordisk's long-acting amylin analog. Studied alone (11.5% weight loss at 68 weeks in REDEFINE 1) and as the amylin component of CagriSema combined with semaglutide. Distinct mechanism from GLP-1 agonists — works on amylin receptors that signal satiety via the brainstem.
- Survodutide
Boehringer Ingelheim and Zealand Pharma's investigational dual agonist of GLP-1 and glucagon receptors. Phase 2 reported up to 19% weight loss at 46 weeks. The phase 3 SYNCHRONIZE program is enrolled; not yet FDA-approved.
View term page →GLP-1 pipeline: survodutide, MariTide, ecnoglutide →
- MariTide (Maridebart Cafraglutide)
Amgen's investigational once-monthly conjugate combining a GLP-1 receptor agonist with a GIP receptor antagonist. Phase 2 (NEJM 2025) reported 16-20% weight loss. The mechanism is unique: opposite GIP direction versus tirzepatide (which is a GIP agonist). Not yet FDA-approved.
View term page →GLP-1 pipeline: survodutide, MariTide, ecnoglutide →
- Ecnoglutide
Sciwind Biosciences' biased GLP-1 receptor agonist (licensed to Pfizer for China). Phase 3 SLIMMER trial reported positive results in Lancet Diabetes Endocrinology 2025. Approved by China's NMPA. Not FDA-approved and not in active US development.
View term page →GLP-1 pipeline: survodutide, MariTide, ecnoglutide →
Mechanism
How GLP-1 receptor agonists work — receptors, gastric emptying, and the satiety pathway.
- GLP-1 receptor
G-protein coupled receptor that responds to glucagon-like peptide-1. Activation by GLP-1 medications suppresses appetite, slows gastric emptying, and improves glucose-dependent insulin secretion.
- GIP receptor
Glucose-dependent insulinotropic polypeptide receptor. Tirzepatide is a dual agonist of both GLP-1 and GIP receptors, which is the proposed basis for its larger gastric-emptying delay than the semaglutides.
- Dual agonist
A medication that activates two receptors at once. Tirzepatide is the GLP-1/GIP dual agonist currently on the market; CagriSema (cagrilintide + semaglutide) and survodutide (GLP-1/glucagon) are in late-stage trials.
View term page →GLP-1 pipeline: survodutide, maridebart, ecnoglutide →
- Gastric emptying
The rate at which food and oral medications leave the stomach. GLP-1 medications slow gastric emptying — the same mechanism that produces appetite suppression also drives the oral-contraceptive and levothyroxine drug interactions.
- Food noise
Patient term for persistent intrusive thoughts about food and eating. Most patients on GLP-1s report food noise reducing within the first 4-8 weeks. Not a formal medical term but widely reported in cohort studies.
- Triple agonist
A peptide that activates three different metabolic receptors simultaneously — typically GIP, GLP-1, and glucagon. Retatrutide is the first triple agonist in clinical development for weight loss. The glucagon component is hypothesized to add an energy-expenditure effect on top of GLP-1 and GIP appetite suppression.
- Amylin
A pancreatic hormone co-secreted with insulin that signals satiety via brainstem receptors. Long-acting amylin analogs (cagrilintide) are being studied alone and combined with GLP-1 drugs (CagriSema) to amplify weight loss beyond what GLP-1 monotherapy achieves. Distinct receptor pathway from GLP-1.
Major trials
The pivotal Phase 3 trials and post-approval cardiovascular, kidney, and sleep-apnea outcome studies.
- STEP-1
Pivotal Phase 3 trial of semaglutide 2.4 mg weekly vs placebo in 1,961 adults with overweight/obesity (Wilding et al, NEJM 2021, PMID 33567185). Mean weight loss 14.9% at 68 weeks.
- SURMOUNT-1
Pivotal Phase 3 trial of tirzepatide 5/10/15 mg weekly vs placebo in 2,539 adults with overweight/obesity (Jastreboff et al, NEJM 2022, PMID 35658024). Mean weight loss 20.9% at 15 mg over 72 weeks.
- SELECT
Cardiovascular outcomes trial of semaglutide 2.4 mg in 17,604 non-diabetic adults with overweight/obesity and established CV disease (Lincoff et al, NEJM 2023). Major adverse cardiovascular events reduced 20% (HR 0.80, 95% CI 0.72-0.90).
- FLOW
Trial of semaglutide 1 mg weekly in chronic kidney disease + type 2 diabetes (NEJM 2024). Composite kidney outcome (eGFR decline, kidney failure, renal/CV death) reduced 24%, HR 0.76.
- SURMOUNT-OSA
Trial of tirzepatide 10/15 mg weekly in obstructive sleep apnea + obesity. Apnea-hypopnea index improved approximately 50% in the tirzepatide arm vs placebo.
- STEP-TEENS
Trial of semaglutide 2.4 mg in adolescents 12-17 with obesity (Weghuber et al, NEJM 2022). Mean weight reduction 16.7% vs 0.6% placebo. Pediatric trials do not measure facial appearance as an outcome.
Side effects
Adverse events on the FDA labels, with the canonical evidence anchors.
- Cholelithiasis
Gallstones. Listed in Section 5 of every FDA-approved GLP-1 label. Wegovy reports 1.6% vs 0.7% placebo; Saxenda reports 2.2% vs 0.8%. The He et al 2022 meta-analysis pooled the GLP-1 risk at RR 1.37 (95% CI 1.23-1.52).
- Ileus
Functional bowel obstruction. Added to Section 6.2 (Postmarketing Experience) of every GLP-1 label in 2023. Sodhi JAMA 2023 cohort found HR 4.22 for bowel obstruction; the Ueda Scandinavian cohort 2024 found HR 0.83 — evidence is mixed.
- Telogen effluvium
Diffuse hair shedding triggered by rapid weight loss or metabolic stress. Typically self-resolving over 3-6 months with adequate protein and micronutrient intake.
- Ozempic face
Patient term for facial volume loss with rapid weight loss on a GLP-1. The 2025 Otolaryngology imaging cohort (PMID 40407186) quantified it at median 9% midfacial volume loss with about 7% loss per 10 kg total weight lost.
- Medullary thyroid carcinoma (MTC)
Rare neuroendocrine tumor of thyroid C-cells. GLP-1 medications carry a black-box warning based on rodent data; no increased human MTC incidence has been demonstrated. Contraindicated in patients with personal/family history of MTC or MEN-2.
- Lean mass loss
Loss of muscle, bone, and other non-fat tissue with rapid weight loss. STEP-1 DEXA sub-analysis found roughly 39% of weight lost was lean mass. Mitigated with adequate protein and resistance training.
View term page →Semaglutide and muscle mass: STEP DEXA sub-analyses →
Pharmacy and drug forms
Compounded vs FDA-approved, 503A vs 503B, and the accreditation programs that distinguish them.
- Compounded GLP-1
Prescription GLP-1 medications prepared from bulk active ingredient by a 503A or 503B pharmacy rather than the FDA-approved branded product. Legality and quality vary; FDA-approved products are off the shortage list as of late 2024.
- 503A pharmacy
Traditional state-licensed compounding pharmacy that prepares medications for individual patients with a prescription. Subject to USP <797> standards but not FDA pre-approval of finished products.
- 503B outsourcing facility
FDA-registered facility licensed to compound medications without a patient-specific prescription, in larger volumes than a 503A. Subject to FDA inspection and stricter quality oversight than 503A.
- PCAB accreditation
Pharmacy Compounding Accreditation Board certification, administered by ACHC. A voluntary third-party quality program covering sterility, potency verification, and facility standards. Required for some 503B outsourcing facilities.
Insurance and regulatory
Coverage barriers, FDA enforcement, and the off-label vs on-label distinction.
- FDA Warning Letter
Formal FDA enforcement document citing specific regulatory violations and demanding corrective action. We track every warning letter sent to compounded GLP-1 telehealth providers and pharmacies.
View term page →FDA warning letters to GLP-1 providers (live database) →
- Step therapy
Insurance requirement to try cheaper or older medications before authorizing newer/more expensive options. A common access barrier for GLP-1 weight-loss drugs.
View term page →GLP-1 insurance coverage: Medicare, Medicaid, commercial →
- Off-label use
Prescribing an FDA-approved drug for a condition or population not on its label. Legal and common — Ozempic for weight loss is the canonical example. Insurance coverage may not extend to off-label indications.
- FDA Drug Shortage List
Public FDA database tracking medications in short supply. Compounded GLP-1s were widely produced under the shortage exemption while semaglutide and tirzepatide were on the list (off the list as of late 2024).
View term page →Compounded GLP-1 price movement (12-month analysis) →
Dosing
Titration, half-life, washout, and missed-dose practical concepts.
- Titration
Gradual dose escalation to minimize side effects. Tirzepatide's standard schedule steps every 4 weeks (2.5 → 5 → 7.5 → 10 → 12.5 → 15 mg). Slower titration reduces nausea and the rate of facial volume change.
- Half-life
Time for plasma concentration to fall by half. Semaglutide ~7 days. Tirzepatide ~5 days. Liraglutide ~13 hours (daily dosing). Orforglipron ~36 hours. Determines weekly vs daily dosing and washout timing.
- Washout period
Time between stopping one GLP-1 and starting another (or before pregnancy planning). The Wegovy label recommends discontinuing at least 2 months before a planned pregnancy.
- Missed dose
Skipped weekly injection. For semaglutide and tirzepatide: take within 5 days of the missed dose; if more than 5 days have passed, skip the missed dose and resume the schedule.
Patient experience
Plain-language patient-community terms — plateau, microdosing, switching.
- Plateau
Stalling weight loss after months of progress. Mechanisms include metabolic adaptation, behavior drift, and dose ceiling. Often resolves with re-titration, dietary review, or resistance training.
- Microdosing
Off-label use of sub-therapeutic GLP-1 doses to minimize side effects or extend supply. Limited evidence; the published RCT data was conducted at the FDA-approved doses.
- Switching GLP-1s
Moving from one GLP-1 to another (e.g., semaglutide to tirzepatide). Generally requires re-titration; the prior drug's washout time and the new drug's titration plan both matter.
Looking for more depth?
The glossary is the index. The deep evidence lives in our research articles, tools, and provider reviews:
- Research articles — 100+ PubMed-cited deep dives.
- Tools and calculators — 27 interactive utilities (titration planner, drug interaction checker, missed-dose guide, washout calculator, and more).
- Compare providers — filterable table of 158+ GLP-1 telehealth providers.
- FDA warning letters database — every FDA warning letter sent to a compounded GLP-1 telehealth provider or pharmacy, updated bi-weekly.