Tirzepatide

Deep dive

Tirzepatide: complete reference

Tirzepatide is a synthetic dual GIP/GLP-1 receptor agonist developed by Eli Lilly, distinguished from earlier GLP-1 monotherapies by its simultaneous activation of two incretin receptors. Structurally, tirzepatide is a 39-amino-acid linear peptide based on the GIP sequence with modifications (including a C20 fatty diacid chain via gamma-glutamic-acid linker) that enable albumin binding and a circulating half-life of approximately 5 days — supporting once-weekly subcutaneous dosing. The dual mechanism is believed to drive its superior weight-loss outcomes vs single-receptor GLP-1 agonists, though the precise contribution of GIP receptor activation is still being characterized. FDA approval came in 2022 (Mounjaro for type 2 diabetes), with Zepbound following in 2023 for chronic weight management and 2024 for moderate-to-severe obstructive sleep apnea. Pivotal trials (SURPASS for diabetes, SURMOUNT for weight, SURMOUNT-OSA for sleep apnea) have produced the highest weight-loss outcomes seen in any FDA-approved anti-obesity medication: 22.5% average body weight reduction at 72 weeks (SURMOUNT-1, 15mg dose). Cardiovascular outcomes are being studied in the ongoing SURPASS-CVOT trial.

In practice

Tirzepatide is the same molecule whether sold as Mounjaro (diabetes label) or Zepbound (weight + OSA label). Same Eli Lilly factory, same doses (2.5-15mg weekly), same side effects — only the FDA indication and brand name differ.

Clinical context

Tirzepatide is the only FDA-approved dual GIP/GLP-1 agonist as of 2026. Clinicians often choose tirzepatide over semaglutide when maximum weight loss is the priority and the patient tolerates it.