The receptor difference
Semaglutide is a GLP-1 receptor agonist. It suppresses appetite, slows gastric emptying and increases glucose-dependent insulin secretion through one pathway. Tirzepatide activates GLP-1 and GIP receptors. The added GIP arm appears to improve insulin sensitivity and lipid handling while possibly reducing some of the nausea that limits pure GLP-1 dosing.
What the head-to-head trial shows
In SURMOUNT-5, tirzepatide produced greater mean weight loss and larger HbA1c reductions than semaglutide in adults with obesity or overweight and type 2 diabetes. The gap is clinically meaningful but not universal: individual response varies, and both drugs require slow dose escalation to be tolerable.
Dosing and administration
Both are injected subcutaneously once weekly and follow a gradual titration. Semaglutide’s label steps up to 2.4 mg over roughly 16 weeks; tirzepatide’s label steps up to 15 mg in 2.5 mg increments. Faster escalation usually means more nausea, vomiting and dropout, so the schedule is part of the therapy, not just a convenience.
Shared risks and practical concerns
Both compounds share the incretin side-effect profile: nausea, diarrhoea, constipation, gallbladder events and appetite suppression severe enough to cause under-eating. Both can produce fat loss alongside lean mass loss, which makes protein intake and resistance training important. Neither is appropriate for anyone with a personal or family history of medullary thyroid carcinoma or MEN2.
Legal status and supply
Semaglutide and tirzepatide are both FDA-approved and prescription-only in the United States. Semaglutide is marketed for type 2 diabetes and chronic weight management under different brand names and dose strengths. Tirzepatide has approved indications for type 2 diabetes and obesity. Any compounded, research-grade or imported version sits outside the verified supply chain and carries additional purity and dosing risks.