Semaglutide

Semaglutide is the most clinically validated GLP-1 receptor agonist for longevity-relevant outcomes. It is a prescription medicine approved for type 2 diabetes (Ozempic, Rybelsus) and chronic weight management (Wegovy), not a research chemical.

The mechanism is well-mapped. Semaglutide mimics the incretin hormone GLP-1, binding GLP-1 receptors on pancreatic beta cells to stimulate glucose-dependent insulin secretion. It suppresses glucagon, slows gastric emptying, and acts on hypothalamic appetite centers to reduce food intake and increase satiety.

The STEP 1 trial (N=1,961, 68 weeks) established weight-loss efficacy at 14.9% mean body weight reduction with 2.4 mg weekly versus 2.4% with placebo. The SELECT trial (N=17,604, mean follow-up 40 months) is the critical longevity finding: semaglutide reduced major adverse cardiovascular events (MACE) by 20% (HR 0.80, 95% CI 0.72-0.90, p<0.001) in adults with established cardiovascular disease and overweight/obesity without diabetes. All-cause death was 4.3% vs 5.2% (HR 0.81, 95% CI 0.71-0.93). This is the only GLP-1 agonist among the four compared here with a completed dedicated cardiovascular outcomes trial in patients without diabetes.

Body composition is the key longevity concern. The SEMALEAN study (N=106 completed, 12-month DXA follow-up, Rouen University Hospital) tracked fat mass and lean mass on semaglutide 2.4 mg. A separate 2025 review documents accelerated sarcopenia risk in older adults on semaglutide therapy, a specific concern for a population already prone to age-related muscle loss. Across the GLP-1 class, lean mass typically comprises 20-40% of total weight lost, prompting strategies such as resistance training to minimize muscle loss.

Beyond weight loss, GLP-1 receptor agonists as a class show anti-inflammatory effects including modulation of NF-kB and NLRP3 inflammasome signaling. A systematic review found GLP-1 receptor agonist treatment (6 months or longer) associated with NASH resolution (OR 4.45, 95% CI 1.92-10.3) across 3 studies. Neuroprotective mechanisms proposed for the class include restoration of neuronal insulin signaling, improved mitochondrial function and mitophagy, reduced tau phosphorylation and amyloid-beta burden, and reduced neuroinflammation via NF-kB/NLRP3 inhibition in Alzheimer's disease models.

Safety is well-characterized from large trial programs. Common adverse effects are gastrointestinal: nausea, vomiting, diarrhea, constipation. Semaglutide carries a boxed warning for thyroid C-cell tumors based on rodent studies and is contraindicated in patients with personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). Risk of acute pancreatitis is described in FDA labeling.