Tirzepatide — questions, answered plainly.

Tirzepatide is a synthetic 39-residue lipidated peptide that activates both the GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors. It is FDA-approved for two distinct indications under two brand names: Mounjaro and Zepbound.

Mounjaro is the brand approved by the FDA for type 2 diabetes mellitus. Zepbound is the same active compound approved for chronic weight management in adults with obesity or overweight plus at least one weight-related condition. Same molecule, two indication-specific brands.

SURPASS is the Phase III clinical trial programme for tirzepatide in type 2 diabetes. SURPASS-1 (Rosenstock 2021, Lancet, PMID 34186022) was the placebo-controlled monotherapy trial in adults with T2D (n=478) and reported superior glycaemic control and weight reduction versus placebo.

SURMOUNT is the Phase III programme for tirzepatide in obesity. SURMOUNT-1 (Jastreboff 2022, NEJM, PMID 35658024) was the obesity trial without T2D (n=2539) reporting mean weight reductions of approximately 15–21% over 72 weeks across doses versus 3% with placebo.

Tirzepatide activates two incretin receptors — GIP and GLP-1 — simultaneously. GLP-1 receptor agonism (older drugs like liraglutide and semaglutide) augments glucose-dependent insulin secretion and reduces appetite. Combining it with GIP receptor activation distinguishes tirzepatide pharmacologically.

Garvey 2023 (Lancet, PMID 37385275) reported that in adults with obesity and type 2 diabetes (n=938), tirzepatide 10–15 mg weekly was associated with mean body weight reductions of 12.8–14.7% over 72 weeks versus 3.2% with placebo.

Long-term cardiovascular outcome trials and oncologic safety studies are ongoing. This profile summarises the primary registrational Phase III evidence; clinical decisions involving tirzepatide are made with a qualified healthcare professional.