Tirzepatide
| Category | Metabolic & GLP-1 |
| Goals | Fat Loss |
| Evidence level | Approved (large Phase 3 RCTs; FDA-approved) |
| Legal status | Prescription drug — FDA-approved |
| FDA status | Mounjaro (T2D, 2022); Zepbound (obesity, 2023; OSA, 2024) |
| Half-life | ~5 days (once-weekly) |
| Routes | Subcutaneous |
| CAS / MW / Sequence | 2023788-19-2 · ~4813.5 g/mol · 39-aa engineered peptide (complex) |
| Last reviewed | 2026-06-07 |
In one line
A once-weekly dual GIP/GLP-1 receptor agonist that produces some of the largest weight-loss results of any approved drug — up to ~20.9% mean body weight in trials.
Evidence at a glance
Tirzepatide has strong human evidence: the SURMOUNT (obesity) and SURPRESS/SURPASS (diabetes) Phase 3 programs are large, randomized, placebo- and active-controlled trials. It is FDA-approved as Mounjaro (type 2 diabetes) and Zepbound (obesity, obstructive sleep apnea). See Evidence Grading Explained and the Disclaimer.
Key Takeaways
- First-in-class dual incretin agonist — activates both the GIP and GLP-1 receptors with a single molecule.
- Delivered ~15–21% mean body-weight reduction across SURMOUNT-1 dose arms over 72 weeks — outperforming Semaglutide head-to-head in SURMOUNT-5.
- FDA-approved for type 2 diabetes (Mounjaro), chronic weight management and obstructive sleep apnea (Zepbound).
- Once-weekly subcutaneous injection; dose is escalated slowly to limit GI side effects.
- The 2024–2025 shortage resolution ended legal compounding of tirzepatide copies (503A: Feb 19, 2025; 503B: Mar 19, 2025).
What Is It
Tirzepatide is a synthetic 39-amino-acid peptide engineered from the native human GIP sequence and modified to also activate the GLP-1 receptor. A C20 fatty-diacid chain attached via a linker lets it bind albumin, extending its half-life to about 5 days and enabling once-weekly dosing. It is the active ingredient in Mounjaro (type 2 diabetes) and Zepbound (weight management; obstructive sleep apnea), both made by Eli Lilly. It was previously known by the development code LY3298176.
Mechanism of Action
Tirzepatide is a dual agonist of two incretin receptors:
- GLP-1 receptor agonism (approved/clinical) — enhances glucose-dependent insulin secretion, suppresses glucagon, slows gastric emptying, and reduces appetite via central pathways.
- GIP receptor agonism (approved/clinical) — adds insulinotropic effect and is thought to improve insulin sensitivity and lipid handling; the GIP component is hypothesized to amplify weight loss and improve GI tolerability relative to GLP-1 alone.
- Notably, tirzepatide is a biased/imbalanced agonist, with relatively greater intrinsic activity at the GIP receptor.
Why "dual" matters
Combining GIP and GLP-1 activity in one molecule appears to produce greater glycemic and weight effects than GLP-1 mono-agonists in head-to-head trials, though the precise contribution of the GIP arm in humans is still being characterized.
Evidence by Outcome
| Outcome | Evidence | Notes |
|---|---|---|
| Weight loss (obesity) | Approved | SURMOUNT-1: ~15.0–20.9% mean loss at 72 wks (5/10/15 mg) |
| Glycemic control (T2D) | Approved | SURPASS program; large HbA1c reductions, often superior to comparators |
| Superiority vs semaglutide | Approved | SURMOUNT-5 head-to-head: greater weight loss than 2.4 mg semaglutide |
| Obstructive sleep apnea | Approved | SURMOUNT-OSA: reduced apnea-hypopnea index; FDA-approved Dec 2024 |
| Cardiovascular outcomes | Clinical | SURMOUNT-MMO / SURPASS-CVOT ongoing/reporting; CV benefit being established |
| Heart failure (HFpEF + obesity) | Clinical | SUMMIT: 38% fewer worsening-HF events vs placebo. Lilly withdrew its FDA filing May 2025 (FDA wanted a confirmatory trial); not approved for HFpEF |
| MASH / fatty liver | Clinical | SYNERGY-NASH and related trials show histologic improvement |
Reported Dosing
Not medical advice
The following reflects FDA-labeled titration for the branded products. Dosing must be individualized by a clinician. See Reconstitution & Dosing Math.
| Phase | Dose | Frequency | Notes |
|---|---|---|---|
| Starting | 2.5 mg | Once weekly | Initiation dose; not for glycemic effect |
| Escalation | +2.5 mg every 4 weeks | Once weekly | Titrate as tolerated |
| Maintenance | 5, 10, or 15 mg | Once weekly | Max approved dose 15 mg/week |
Pharmacokinetics
Tirzepatide has a half-life of ~5 days, supporting once-weekly subcutaneous administration. Steady state is reached in about 4 weeks. Albumin binding via the fatty-diacid chain slows clearance. It is metabolized by proteolysis. See Half-Life & Pharmacokinetics.
Side Effects & Risks
- Gastrointestinal — nausea, diarrhea, vomiting, constipation, dyspepsia; most common, dose-dependent, and worst during escalation.
- Hypoglycemia — mainly when combined with insulin or sulfonylureas.
- Gallbladder disease (cholelithiasis), acute pancreatitis (rare), and acute kidney injury secondary to dehydration from severe GI symptoms.
- Boxed warning — risk of thyroid C-cell tumors based on rodent data; contraindicated with personal/family history of medullary thyroid carcinoma or MEN 2.
- Loss of lean mass with rapid weight loss; nutrition and resistance training are commonly advised.
- Sourcing risk — gray-market “research” tirzepatide is not quality-controlled. See Sourcing, Red Flags & Scams.
- See Side Effects & Risk Management and Bloodwork & Monitoring.
Cycling
There is no clinical concept of “cycling” tirzepatide — it is a chronic maintenance therapy. Stopping typically leads to weight regain. Discontinuation should be managed clinically. See Cycling.
Stacks It Appears In
- Used as monotherapy in trials; in practice combined with diet, resistance training, and standard diabetes agents under medical supervision.
Comparisons
Sourcing & Quality
The only quality-assured tirzepatide is the FDA-approved branded product (Mounjaro/Zepbound) via prescription. Following the 2025 shortage resolution, compounded versions are no longer broadly permitted. Gray-market lyophilized “research” tirzepatide carries identity/purity risk — see How to Read a CoA, Red Flags & Scams. Reconstitution and storage: Reconstitution & Dosing Math, Storage & Handling. No vendors are endorsed here.
Legal & Regulatory Status
(As of 2026-06-07.) FDA-approved: Mounjaro for type 2 diabetes (approved 2022-05-13); Zepbound for chronic weight management (approved 2023-11-08) and for moderate-to-severe obstructive sleep apnea in adults with obesity (approved December 2024). A filing for heart failure with preserved ejection fraction (HFpEF) with obesity (SUMMIT trial) was withdrawn by Lilly in May 2025 after the FDA signaled it wanted a confirmatory trial — so HFpEF is not an approved indication as of this review. The FDA declared the tirzepatide shortage resolved in late 2024; enforcement deadlines ended legal compounding on Feb 19, 2025 (503A) and Mar 19, 2025 (503B). The FDA has proposed excluding tirzepatide from the 503B Bulks List. See Regulatory & Legal Status.
FAQ
Is tirzepatide FDA-approved? Yes — as Mounjaro (type 2 diabetes) and Zepbound (obesity; obstructive sleep apnea).
How does it compare to semaglutide? In the SURMOUNT-5 head-to-head trial, tirzepatide produced greater weight loss than 2.4 mg semaglutide. See Semaglutide vs Tirzepatide.
Can I still get compounded tirzepatide? Broad legal compounding ended in early 2025 after the shortage was resolved. Quality-assured product is the branded prescription drug.
Is it injected or oral? Once-weekly subcutaneous injection. There is no approved oral tirzepatide.
References
- Jastreboff A.M. et al. (2022). “Tirzepatide Once Weekly for the Treatment of Obesity” (SURMOUNT-1). New England Journal of Medicine.
- Frías J.P. et al. (2021). “Tirzepatide versus Semaglutide Once Weekly in Type 2 Diabetes” (SURPASS-2). New England Journal of Medicine.
- Aronne L.J. et al. (2025). SURMOUNT-5 head-to-head tirzepatide vs semaglutide. New England Journal of Medicine.
- Malhotra A. et al. (2024). “Tirzepatide for the Treatment of Obstructive Sleep Apnea” (SURMOUNT-OSA). New England Journal of Medicine.
- U.S. FDA approval records — Mounjaro (2022), Zepbound (2023–2024); FDA statements on GLP-1 compounding wind-down (2024–2025).
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