GLP-1 receptor pharmacology

GLP-1 receptor pharmacology is the area of metabolic peptide biology where the rate of evidence accumulation has outrun the field's ability to absorb it. In the span of five years (2021–2026), three molecules have either reached FDA approval (Semaglutide as Wegovy, 2021; Tirzepatide as Zepbound, 2023) or produced Phase 2 data that exceeds previous obesity-pharmacotherapy benchmarks by wide margins (Retatrutide, 2023). The category went from "promising adjunct to lifestyle intervention" to "intervention with effect sizes previously confined to bariatric surgery" within one regulatory cycle.

This dossier surveys what the GLP-1 receptor pharmacology actually does, how the three compounds in this corpus differ in receptor engagement (single-receptor versus dual versus triple agonism), what the pivotal trial evidence supports for each, and which of the public controversies around the class — gastrointestinal side effects, body composition, discontinuation rebound, emerging signals — survive contact with the underlying literature.

The three compounds split along receptor-engagement breadth: Semaglutide is a GLP-1 monoagonist; Tirzepatide is a dual GIP / GLP-1 agonist; Retatrutide is a triple GIP / GLP-1 / glucagon agonist. The progression is not arbitrary — each additional receptor adds a different metabolic mechanism (GIP addresses adipose insulin sensitivity and nausea-pathway signaling; glucagon addresses hepatic glucose output and energy expenditure) — and the empirical effect sizes track the breadth of receptor engagement.

The practical clinical questions are not whether the molecules work but at what cost, how durable the benefits are, and what the long-tail safety story will look like at decade-plus exposures the trial program has not yet covered.