Metabolic GLP-Axis

Definition

Metabolic GLP-Axis peptides are incretin and amylin-mimetic compounds that act on receptors in the pancreas, gut, and central nervous system to regulate appetite, insulin secretion, glucagon suppression, and body weight. This category encompasses GLP-1 receptor agonists (GLP-1RAs), dual GLP-1/GIP agonists, triple agonists, and amylin co-agonists — the most pharmacologically mature peptide class in clinical use today. Semaglutide and tirzepatide have become household names; retatrutide and cagrilintide represent the next generation currently clearing Phase III trials.

Mechanism of Action

GLP-1 receptors are expressed throughout the body — in pancreatic beta cells (insulin secretion), the hypothalamus and brainstem (satiety signaling), the stomach (delayed gastric emptying), and cardiovascular tissue (cardioprotective effects). GLP-1 receptor agonism reduces glucagon, slows nutrient absorption, and generates dose-dependent satiety via central pathways. Dual GLP-1/GIP agonists like tirzepatide add potentiation through the GIP receptor, which amplifies insulin release and fat cell browning. Triple agonists (GLP-1/GIP/glucagon) like retatrutide further increase energy expenditure via glucagon receptor co-activation. Cagrilintide mimics amylin to slow gastric emptying and reduce caloric intake through a complementary, non-incretin pathway.

Regulatory Status

Semaglutide (Ozempic for T2D, Wegovy for obesity) and liraglutide (Victoza, Saxenda) are FDA-approved. Tirzepatide (Mounjaro for T2D, Zepbound for obesity) is FDA-approved. Retatrutide is in Phase III trials. Cagrilintide is in Phase III as part of the CagriSema combination. Compounding of semaglutide and tirzepatide was permitted under shortage conditions; FDA has issued guidance actively restricting compounding of these approved molecules as supply normalizes.

Evidence Base

The evidence base for this category is the strongest of all twelve classes. Landmark randomized controlled trials — SCALE, SUSTAIN, SURMOUNT, SURPASS — demonstrate 10–22% body weight reduction with sustained cardiovascular, renal, and hepatic benefits. The SELECT trial (semaglutide) showed a 20% reduction in major adverse cardiovascular events in non-diabetic patients with obesity. Combination agents like CagriSema are tracking above 20% weight loss in Phase III.