Glossary: the terms used on every GLP-1 entry

Definitions are written for a reader with no pharmacology, and are kept to what the entries need. Where a definition depends on a label or FDA page, that source is listed above.

The hormones

Incretin. A gut hormone released after eating that increases insulin secretion in a glucose-dependent way. The two human incretins are GLP-1 and GIP. "Incretin drugs" is the umbrella term for this whole site.

GLP-1 (glucagon-like peptide-1). A 30-amino-acid hormone from the intestinal L cells. Raises insulin when glucose is high, lowers glucagon, slows gastric emptying, reduces appetite. Lasts minutes in the blood because DPP-4 destroys it.

GIP (glucose-dependent insulinotropic polypeptide). The other incretin, from the K cells of the upper gut. Alone it is a weak drug; combined with GLP-1 activity in tirzepatide it is part of the strongest approved agent.

Glucagon. The hormone that raises blood glucose from the liver. Glucagon receptor activation also increases energy expenditure and liver fat oxidation, which is why survodutide, mazdutide and retatrutide include it alongside GLP-1 activity to offset the glucose effect.

Amylin. A hormone co-secreted with insulin from the beta cell that slows gastric emptying and reduces food intake through a central pathway separate from GLP-1's. Cagrilintide, the second component of CagriSema, is a long-acting amylin analogue.

The drugs

Receptor agonist. A molecule that binds a receptor and switches it on, as the natural hormone would. Every agent on this site is an agonist; none is a blocker.

Analogue. A modified version of the human hormone. Liraglutide (97% homology to GLP-1) and semaglutide (94%) are analogues. Exenatide and lixisenatide are not analogues of human GLP-1; they are based on exendin-4, a lizard peptide that happens to fit the human receptor.

Dual agonist, triple agonist. One molecule that activates two receptors (tirzepatide: GIP and GLP-1; survodutide and mazdutide: glucagon and GLP-1) or three (retatrutide: GIP, GLP-1 and glucagon). CagriSema is not a dual agonist in this sense; it is two separate peptides given together.

Peptide. A short chain of amino acids. Twelve of the thirteen entries are peptides. Peptides are digested if swallowed (hence injections, and the special formulation of oral semaglutide), are broken down by proteases rather than liver enzymes, and can provoke antibodies.

Small molecule. A conventional drug molecule, made by chemical synthesis, absorbed from an ordinary tablet and cleared by liver enzymes. Orforglipron (Foundayo) is the only small molecule on this site, which is why it is the only entry with CYP3A4 interaction rules.

Half-life. The time for the blood level to fall by half. Native GLP-1: minutes. Exenatide: hours (twice daily). Liraglutide: about a day (once daily). Semaglutide, dulaglutide, tirzepatide: about a week (once weekly). The labels give the exact figures.

DPP-4 (dipeptidyl peptidase-4). The enzyme that cleaves native GLP-1 and GIP within minutes. Every peptide agent is engineered to resist it; the DPP-4 inhibitor drugs (sitagliptin, the comparator in AWARD-5) work by blocking the enzyme instead.

Albumin binding. The trick behind liraglutide, semaglutide and tirzepatide: a fatty-acid side chain lets the peptide ride on albumin, the most abundant blood protein, which slows kidney clearance and protects against enzymes. The Mounjaro label names tirzepatide's C20 fatty diacid; the Ozempic label describes albumin binding as the principal mechanism of protraction.

Fusion protein. A peptide joined to a large carrier protein so it lasts longer. Dulaglutide (antibody Fc fragment) and albiglutide (albumin) are fusion proteins.

SNAC (salcaprozate sodium). The absorption enhancer co-formulated with oral semaglutide that lets a fraction of the peptide cross the stomach lining. It is why Rybelsus, Ozempic tablets and Wegovy tablets must be taken fasting with up to 4 ounces of water and a 30-minute wait.

CYP3A4, OATP1B. A liver enzyme and a liver transporter that clear many drugs. The Foundayo label caps the dose at 9 mg with a strong CYP3A4 inhibitor and says to avoid strong inducers; no peptide label has an equivalent rule.

The label

Prescribing information (label). The FDA-agreed document that accompanies an approved drug: indications, dosing, contraindications, warnings, adverse reactions, pharmacology, trial summaries. The adverse-reaction and dosing tables on this site are copied from it.

Boxed warning. The most prominent warning FDA requires, printed in a box at the top of the label. For this class it is the risk of thyroid C-cell tumors: the long-acting agents caused C-cell tumors in rodents at clinically relevant exposures, human relevance is unknown, and the drugs are contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2. Byetta and Adlyxin have no boxed warning; orforglipron carries it by class even though it is inactive in rodents.

MTC, MEN 2. Medullary thyroid carcinoma, a cancer of the thyroid C cells; Multiple Endocrine Neoplasia syndrome type 2, an inherited condition that predisposes to it. Both are contraindications in every boxed warning on this site.

Adverse reaction. An unwanted effect judged to be caused by the drug. Labels report the percentage of trial patients with each reaction in the drug arm and the placebo arm; the difference is the excess attributable to the drug. Rates from different trials cannot be compared directly, and every label says so.

Indication. A condition the drug is approved to treat, stated in section 1 of the label. Everything else is off-label.

Titration, escalation. Starting at a low dose and increasing at set intervals to reduce gastrointestinal reactions. Every entry's dosing table is an escalation schedule from the label.

The regulator

Drugs@FDA. FDA's public database of approved drugs: application numbers, approval dates, marketing status, labels and letters. The record this site checks first.

NDA, BLA. New Drug Application and Biologics License Application, the two routes to approval. Most agents here are NDAs; dulaglutide, albiglutide and (after a 2020 transition) lixisenatide are BLAs. ANDA is the generic route.

Supplement (S-number). A change to an approved application: a new indication, dose, population or label wording. Supplements have their own approval dates and letters; "Wegovy S-029" is the March 2026 supplement that added the 7.2 mg dose.

Accelerated approval. Approval based on an endpoint reasonably likely to predict benefit, with a confirmatory trial required. Wegovy's MASH indication is one.

Marketing status: discontinued. The sponsor no longer markets the product; the approval remains. Exenatide and albiglutide products are in this state.

Investigational. Studied under an Investigational New Drug application; not approved. Four entries.

503A, 503B. The two sections of the Food, Drug and Cosmetic Act that permit compounding: 503A for a licensed pharmacy filling individual prescriptions, 503B for registered outsourcing facilities producing in bulk. Compounded drugs under either section are not FDA approved.

The trials

Phase 2, phase 3. Phase 2 finds the dose in a few hundred people; phase 3 tests it in thousands against placebo or an active drug and is the basis for approval. The investigational entries quote both; the approved entries quote phase 3.

Placebo-adjusted. The drug arm's result minus the placebo arm's. The comparison table computes it for weight change.

Hazard ratio (HR). In an outcome trial, the rate of events on the drug relative to the comparator over time. 0.80 means 20% fewer events; a 95% confidence interval that crosses 1.00 means the difference was not statistically significant.

MACE. Major adverse cardiovascular events: the composite of cardiovascular death, non-fatal heart attack and non-fatal stroke used as the primary endpoint in SELECT, SUSTAIN-6, LEADER, REWIND, EXSCEL, ELIXA, Harmony Outcomes and SURPASS-CVOT.

Non-inferiority, superiority. Two different tests. Non-inferiority shows the drug is not meaningfully worse than the comparator (the safety question FDA required of this class); superiority shows it is better. EXSCEL and ELIXA met the first and not the second; SURPASS-CVOT met non-inferiority against dulaglutide.

HbA1c. Glycated hemoglobin, the three-month average blood glucose, reported in percentage points. The diabetes trials' primary endpoint.

Estimand. The precise question a trial statistic answers, in particular how it treats people who stopped the drug. "Treatment policy" counts everyone as randomized; "trial product" counts only time on drug. The PIONEER 1 abstract reports both, which is why two sets of numbers appear on the oral semaglutide entry.

PubMed id (PMID). The National Library of Medicine's record number for a paper. Every trial on this site is cited by it so you can read the abstract yourself.