What Is Tirzepatide?
Tirzepatide is a dual agonist that activates both GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) receptors. It is manufactured by Eli Lilly and sold under two brand names: Mounjaro, approved for Type 2 diabetes in May 2022, and Zepbound, approved for chronic weight management in November 2023.
The addition of GIP receptor agonism is what makes tirzepatide different from semaglutide. GIP works synergistically with GLP-1 to enhance insulin secretion, reduce appetite, and promote fat breakdown — producing greater overall efficacy than either mechanism alone.
The SURMOUNT Trials
The SURMOUNT-1 trial was the pivotal study supporting Zepbound's approval. Over 72 weeks, participants taking the highest dose of tirzepatide (15 mg) lost an average of 22.5% of their body weight. Approximately 34% of participants lost 25% or more — results that represent the highest efficacy ever demonstrated by an approved weight loss medication.
Mounjaro vs. Zepbound: Same Drug, Different Indication
Mounjaro and Zepbound contain the same molecule at the same doses. Mounjaro carries FDA approval for Type 2 diabetes; Zepbound carries approval for obesity. Insurance coverage differs depending on the indication. Some patients access tirzepatide through a Mounjaro prescription when Zepbound coverage is not available or affordable.
Titration Schedule
Tirzepatide starts at 2.5 mg weekly and increases by 2.5 mg every four weeks until reaching a maintenance dose of 5 mg to 15 mg depending on response and tolerability.
July 2026 Update: Medicare GLP-1 Bridge
Medicare GLP-1 Bridge (Launched July 1, 2026): CMS launched a short-term demonstration program providing eligible Medicare Part D beneficiaries access to certain GLP-1 medications — including Zepbound — for approximately $50/month. The program runs through December 31, 2027. Coverage is administered through a central processor outside the standard Part D benefit, so pharmacies and plans do not need to opt in for eligible beneficiaries to access it. Eligible patients should speak with their prescriber or pharmacist.
Nutrition on Tirzepatide
The appetite suppression from tirzepatide is often described as more consistent and profound than with semaglutide alone. This makes adequate protein intake even more critical — without intentional planning, it is easy to under-eat significantly, accelerating muscle loss. ShedPilot ensures your meals hit protein, fiber, and micronutrient targets even on your lowest appetite days.