Semaglutide

Semaglutide is a glucagon-like peptide-1 (GLP-1) receptor agonist developed by Novo Nordisk. It's a modified version of human GLP-1 with structural changes — including a fatty-acid side chain that binds to albumin in circulation — that extend its half-life to around seven days, making once-weekly dosing feasible. It's the same molecule whether it's branded as Ozempic (for type 2 diabetes), Wegovy (for chronic weight management), or Rybelsus (the oral form for T2D). The FDA first approved semaglutide for T2D in 2017, for cardiovascular risk reduction in 2020, and for chronic weight management in 2021.

GLP-1 is an incretin hormone secreted by intestinal L-cells after eating. Semaglutide activates the GLP-1 receptor across multiple tissues with three clinically important effects: (1) in pancreatic beta cells, it stimulates glucose-dependent insulin secretion and suppresses glucagon release, flattening postprandial glucose excursions; (2) in the gut, it slows gastric emptying, which prolongs satiety after a meal; (3) in central nervous system pathways (particularly the hypothalamus and brainstem), it suppresses appetite and reduces food reward signaling. The weight-loss effect is primarily driven by central appetite suppression, not by GI side effects.

Semaglutide's clinical development for T2D ran through the SUSTAIN trial program (SUSTAIN 1-10, 2016-2020), demonstrating superiority to placebo and to older GLP-1 agonists on HbA1c reduction. Its weight-management story began with the STEP trial program. STEP-1 (published NEJM 2021) enrolled adults with BMI ≥30 or ≥27 with weight-related comorbidity; participants on semaglutide 2.4 mg lost a mean 14.9% of body weight at 68 weeks versus 2.4% on placebo. STEP-2 through STEP-8 extended the evidence base to patients with T2D, adolescents (age 12+, approved 2022), and head-to-head comparisons with liraglutide. In 2024-2025, SURMOUNT-5 provided the first head-to-head RCT versus tirzepatide, with tirzepatide producing greater mean weight loss (20.2% vs 13.7% at 72 weeks).

As of April 2026, semaglutide has completed Phase 3 and carries FDA approvals for T2D (Ozempic, Rybelsus), cardiovascular risk reduction in T2D adults with established CVD (Ozempic), chronic weight management in adults and adolescents (Wegovy), and in August 2024 MACE reduction in adults with obesity/overweight plus established CVD (SELECT trial). Ongoing research areas include heart failure with preserved ejection fraction (STEP-HFpEF positive; FDA approved 2024), chronic kidney disease (FLOW trial, positive), and Alzheimer's disease (evoke/evoke+ trials, readouts expected 2025-2026).

FDA-approved as Ozempic (Dec 2017, T2D), Rybelsus (Sep 2019, oral T2D), Wegovy (Jun 2021, chronic weight management), expanded for CV risk reduction (2020 Ozempic, 2024 Wegovy via SELECT). The FDA declared the semaglutide shortage resolved on Feb 21, 2025; 503A compounding discretion ended Apr 22, 2025; 503B by May 22, 2025. Compounded semaglutide is no longer broadly legal for most US patients. See our FDA timeline for the full enforcement history. Full regulatory timeline →

Three major open questions: (1) muscle and bone loss — observational and trial sub-analyses suggest 25-40% of the weight lost on semaglutide is lean mass, raising concerns for sarcopenia, particularly in older adults. Resistance training and adequate protein intake are the leading countermeasures but neither fully abrogates the effect. (2) Rebound weight gain — the STEP-1 extension (STEP-4) showed significant weight regain after discontinuation, suggesting semaglutide functions more as chronic therapy than a short-course treatment. (3) Rare adverse events — thyroid C-cell tumors (boxed warning based on rodent data; unclear human relevance), pancreatitis (rare), and a 2023-2024 signal around non-arteritic anterior ischemic optic neuropathy (ongoing investigation).

• STEP-1 trial (NEJM, 2021) →
• SELECT trial (NEJM, 2023) →
• SURMOUNT-5 head-to-head vs tirzepatide (NEJM, 2025) →
• FDA Wegovy prescribing information →