Tirzepatide Drug

## What it is Tirzepatide is a synthetic 39-amino-acid peptide and the first dual incretin receptor agonist to reach the market. Developed by Eli Lilly under the code LY3298176, it engages both the glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor with a single molecule. The FDA approved it as Mounjaro for type 2 diabetes in May 2022 and as Zepbound for chronic weight management in adults with a BMI of 30 or higher (or 27 with weight-related comorbidity) in November 2023. The EMA followed with European approvals shortly thereafter. Users fall into three broad groups: adults with type 2 diabetes seeking better glycemic control, adults with obesity using it for chronic weight management, and a smaller off-label cohort using compounded versions during the 2023 to 2024 FDA shortage window. The FDA removed tirzepatide from its shortage list in late 2024, narrowing the legal compounding window considerably. ## Mechanism of action Tirzepatide simultaneously activates two incretin pathways. GLP-1 receptor activation potentiates glucose-dependent insulin secretion from pancreatic beta cells, suppresses glucagon, slows gastric emptying, and acts on hypothalamic and brainstem satiety circuits. GIP receptor activation appears to amplify the insulinotropic effect, modulate adipose tissue handling of glucose and lipids, and may attenuate the GI side effects typical of pure GLP-1 agonism by acting on emetic circuitry differently. The terminal half-life is approximately 5 days, supporting once-weekly subcutaneous dosing. Steady state is reached after roughly 4 weeks at a fixed dose. Onset of metabolic effects begins within 24 hours of the first injection, with peak satiety effects around 72 hours post-dose. ## Evidence base The SURMOUNT-1 trial (n=2539, 72 weeks) reported mean body-weight reductions of approximately 15.0% at 5 mg, 19.5% at 10 mg, and 22.5% at 15 mg weekly versus 2.4% on placebo, all statistically significant. SURMOUNT-2 in adults with both obesity and type 2 diabetes showed roughly 13.4% mean loss at 10 mg and 15.7% at 15 mg over 72 weeks, smaller than in non-diabetic obesity but still substantial. SURPASS-2 (n=1879) ran a head-to-head comparison against semaglutide 1 mg weekly over 40 weeks in adults with type 2 diabetes. Tirzepatide reduced HbA1c by 2.01, 2.24, and 2.30 percentage points at 5, 10, and 15 mg respectively, versus 1.86 for semaglutide 1 mg, with corresponding weight reductions of 7.6 to 11.2 kg versus 5.7 kg. SURPASS-3 added insulin glargine as a comparator and showed superior HbA1c reduction with tirzepatide. SURMOUNT-4 examined withdrawal effects: participants who reached week 36 on tirzepatide and were then randomized to placebo regained a substantial fraction of lost weight over the following 52 weeks, mirroring the rebound pattern seen with semaglutide. Body-composition substudies report that roughly 25% of total mass lost on tirzepatide is lean tissue, slightly less than the 30 to 40% reported in pure GLP-1 monotherapy without resistance training. The SURPASS-CVOT cardiovascular outcomes trial is pending as of 2026. ## Dosage and administration The label titration starts at 2.5 mg subcutaneous weekly for 4 weeks, then escalates by 2.5 mg every 4 weeks to a target of 5, 10, or 15 mg weekly. The 2.5 mg starting dose is intended for tolerability rather than therapeutic effect. Most patients in the obesity indication titrate to the highest tolerated dose, given the dose-response gradient observed in SURMOUNT-1. Injection rotates between abdomen, thigh, and upper arm. Branded pens (Mounjaro, Zepbound) ship pre-filled. Compounded vials typically supply 10 to 30 mg lyophilized powder reconstituted with 1 to 2 mL bacteriostatic water; a 2.5 mg starter draws 8 to 25 units on a U100 insulin syringe depending on final concentration. Tirzepatide is not cycled. It is titrated up over months and continued indefinitely while clinically appropriate. Discontinuation typically results in weight regain over the following year. ## Side effects and safety GI effects dominate the adverse-event profile: nausea (around 18 to 29% across SURMOUNT doses), diarrhea (16 to 23%), vomiting (8 to 13%), and constipation (10 to 17%). These cluster around dose escalations and ease with slow titration. Around 5 to 7% of participants discontinued for GI reasons in SURMOUNT-1. Contraindications include personal or family history of medullary thyroid carcinoma, multiple endocrine neoplasia syndrome type 2, pregnancy, severe gastroparesis, and history of pancreatitis (use caution). Drug interactions include additive hypoglycemia risk with insulin and sulfonylureas (which typically need dose reduction), reduced oral contraceptive exposure for 4 weeks after initiation and each escalation (backup contraception advised), and altered absorption of co-administered oral medications due to delayed gastric emptying. ## Practical notes Branded pens are stored refrigerated (2 to 8 degrees C). Once a pen is in use it can sit at room temperature up to 21 days per Lilly labeling. Compounded vials are typically reconstituted with bacteriostatic water and refrigerated; sterility and stability vary by pharmacy. Expect satiety changes within the first week. The largest weight changes accumulate over months, with the SURMOUNT-1 curves still trending down at week 72. Lean-mass preservation requires deliberate effort: 1.6 to 2.2 g/kg/day protein and consistent resistance training are the standard pairings. Plan for the GI side effects to peak after each escalation and resolve within 1 to 2 weeks.