Peptide Monograph

Tirzepatide

Mounjaro (T2D) · Zepbound (Obesity)

GLP-1/GIP Agonist FDA Approved SubQ

At a Glance

Generic Name Tirzepatide
Trade Names Mounjaro, Zepbound
Class Dual GIP/GLP-1 receptor agonist
FDA Status Approved (2022 T2D; 2023 Obesity)
Molecular Weight 4813.45 Da
CAS Number 2023788-19-2
Half-Life ~120 h (5 days)
Amino Acids 39
Route Subcutaneous injection (weekly)
Dose Range 2.5 – 15 mg/week

Mechanism of Action

Tirzepatide is a first-in-class dual incretin receptor agonist that activates both the glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor.[1] The 39-amino-acid synthetic peptide is based on the native GIP sequence with modifications that confer GLP-1 receptor affinity, and it incorporates a C-20 fatty diacid moiety that enables albumin binding and extends its half-life to approximately five days.[2]

The dual mechanism produces several complementary pharmacological effects:

  • Enhanced insulin secretion: Both GIP and GLP-1 receptor activation potentiate glucose-dependent insulin release from pancreatic beta cells, providing greater glycemic control than either pathway alone.[1]
  • Glucagon suppression: GLP-1 receptor activation reduces inappropriate glucagon secretion from alpha cells, lowering hepatic glucose output.[3]
  • Delayed gastric emptying: GLP-1 receptor signaling slows gastric motility, contributing to both postprandial glucose control and reduced caloric intake.[4]
  • Central appetite suppression: Both GIP and GLP-1 receptors are expressed in hypothalamic and brainstem nuclei regulating energy homeostasis. Dual activation produces robust appetite reduction and caloric deficit.[5]
  • Improved insulin sensitivity: GIP receptor activation may independently improve peripheral insulin sensitivity and promote adipose tissue remodeling, a mechanism not shared by selective GLP-1 agonists.[6]

The synergy between GIP and GLP-1 pathways is hypothesized to account for the superior weight loss and glycemic outcomes observed in head-to-head comparisons with selective GLP-1 receptor agonists such as semaglutide.[7]

Clinical Evidence

SURPASS Trials (Type 2 Diabetes)

The SURPASS clinical development program evaluated tirzepatide across five pivotal Phase 3 trials in patients with type 2 diabetes mellitus (T2D):

  • SURPASS-1 (monotherapy): Tirzepatide 5, 10, and 15 mg reduced HbA1c by 1.87%, 1.89%, and 2.07% respectively versus placebo over 40 weeks. Body weight reductions ranged from 7.0 to 9.5 kg.[8]
  • SURPASS-2 (vs. semaglutide 1 mg): Tirzepatide at all doses demonstrated superiority to semaglutide 1 mg for HbA1c reduction. The 15 mg dose achieved a mean HbA1c reduction of 2.46% vs. 1.86% for semaglutide, with 12.4 kg weight loss vs. 6.2 kg.[1]
  • SURPASS-3 (vs. insulin degludec): Tirzepatide was superior to titrated insulin degludec for HbA1c reduction, with the added benefit of weight loss versus weight gain.[9]
  • SURPASS-4 (vs. insulin glargine, CV outcomes): Tirzepatide was non-inferior to insulin glargine for cardiovascular safety and superior for glycemic control.[10]
  • SURPASS-5 (add-on to insulin glargine): Tirzepatide added to basal insulin produced significant HbA1c and weight reductions versus placebo.[11]

SURMOUNT Trials (Obesity)

The SURMOUNT program evaluated tirzepatide for chronic weight management in adults with obesity or overweight with weight-related comorbidities:

  • SURMOUNT-1: In 2,539 adults without diabetes (BMI ≥30, or ≥27 with comorbidity), tirzepatide 15 mg produced a mean weight reduction of 22.5% (approximately 24 kg) over 72 weeks versus 2.4% with placebo. The 10 mg dose achieved 21.4% and the 5 mg dose achieved 16.0%.[5]
  • SURMOUNT-2: In adults with T2D and obesity, tirzepatide 15 mg produced 14.7% weight loss over 72 weeks, confirming efficacy in the more treatment-resistant diabetic population.[12]
  • SURMOUNT-3: Following a 12-week intensive lifestyle lead-in, tirzepatide produced an additional 18.4% weight loss beyond the lead-in period.[13]
  • SURMOUNT-4: A randomized withdrawal study demonstrated that patients who discontinued tirzepatide regained approximately two-thirds of lost weight over 52 weeks, while those who continued treatment maintained weight loss.[14]
Clinical Significance

The 22.5% mean weight loss achieved with tirzepatide 15 mg in SURMOUNT-1 represents the largest weight reduction reported for any anti-obesity medication in Phase 3 trials as of the publication date, approaching outcomes historically seen only with bariatric surgery.

Primary Uses

FDA-Approved Indications

  • Type 2 diabetes mellitus (Mounjaro): As an adjunct to diet and exercise to improve glycemic control in adults with T2D. Approved May 2022.[15]
  • Chronic weight management (Zepbound): As an adjunct to a reduced-calorie diet and increased physical activity for chronic weight management in adults with an initial BMI of ≥30 kg/m2, or ≥27 kg/m2 with at least one weight-related comorbidity. Approved November 2023.[16]

Investigational Uses

  • Heart failure with preserved ejection fraction (HFpEF) and obesity
  • Metabolic dysfunction-associated steatohepatitis (MASH)
  • Obstructive sleep apnea

Contraindications

Absolute Contraindications

Do not use tirzepatide in patients with any of the following:

  • Personal or family history of medullary thyroid carcinoma (MTC): Tirzepatide carries a boxed warning based on thyroid C-cell tumor findings in rodent studies. Although human relevance is uncertain, the drug is contraindicated in patients with a personal or family history of MTC.[15]
  • Multiple Endocrine Neoplasia syndrome type 2 (MEN 2): Patients with MEN 2 are at elevated risk for MTC and must not receive GLP-1 or dual incretin receptor agonists.[15]
  • Known hypersensitivity: Prior serious hypersensitivity reaction (anaphylaxis, angioedema) to tirzepatide or any excipient.[15]
  • Pregnancy: Tirzepatide may cause fetal harm based on animal data. Women of childbearing potential should discontinue at least 2 months before a planned pregnancy given the drug's extended washout period.[15]

Relative Contraindications / Precautions

  • History of pancreatitis (risk of acute pancreatitis)
  • Severe gastrointestinal disease (gastroparesis, inflammatory bowel disease)
  • History of gallbladder disease (increased risk of cholelithiasis)
  • Diabetic retinopathy (monitor for worsening with rapid glycemic improvement)
  • Concurrent use of sulfonylureas or insulin (hypoglycemia risk; dose reduction may be necessary)
  • Severe renal impairment (limited data; monitor for dehydration from GI side effects)

Standard Protocols

FDA-Approved Titration Schedule (Mounjaro / Zepbound)

Tirzepatide is initiated at a low dose and titrated upward at 4-week intervals to reduce gastrointestinal adverse effects. The titration schedule per the approved prescribing information is:[15]

Period Weeks Dose Notes
Initiation Weeks 1 – 4 2.5 mg Starting dose (not a maintenance dose)
Step 2 Weeks 5 – 8 5 mg First maintenance dose option
Step 3 Weeks 9 – 12 7.5 mg Intermediate step
Step 4 Weeks 13 – 16 10 mg Second maintenance dose option
Step 5 Weeks 17 – 20 12.5 mg Intermediate step
Step 6 Weeks 21+ 15 mg Maximum maintenance dose
Clinical Note

The 2.5 mg dose is an initiation dose only and is not intended for chronic use. Patients should be advanced to at least 5 mg after the initial 4-week period. Dose escalation should be guided by tolerability; patients experiencing significant GI adverse effects may remain at their current dose for an additional 4 weeks before escalating.

Administration

  • Inject subcutaneously in the abdomen, thigh, or upper arm once weekly
  • Rotate injection sites with each dose
  • Administer on the same day each week; the day may be changed as long as the last dose was at least 3 days prior
  • May be administered with or without food
  • Supplied as a single-dose pre-filled pen (KwikPen); no reconstitution required

Stacks & Combinations

Tirzepatide is typically used as monotherapy or in combination with other glucose-lowering agents in the T2D setting. Common co-administered therapies include:

  • Metformin: Most common combination. Studied extensively in SURPASS trials. Complementary mechanisms with additive glycemic benefit.[1]
  • SGLT2 inhibitors: Mechanistically complementary (renal glucose excretion). May offer additive cardiorenal benefits. Limited direct combination data but commonly used in clinical practice.
  • Basal insulin: SURPASS-5 demonstrated tirzepatide added to insulin glargine. Consider reducing insulin dose when initiating tirzepatide to minimize hypoglycemia risk.[11]
Caution

When combining tirzepatide with sulfonylureas or insulin, the risk of hypoglycemia is increased. Consider reducing the sulfonylurea or insulin dose when initiating tirzepatide.

Preparation & Administration

Commercial Pre-Filled Pens

Tirzepatide is commercially available as Mounjaro and Zepbound single-dose, disposable pre-filled pens (KwikPen). No reconstitution or dose calculation is required. Available pen strengths: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg per 0.5 mL.

Injection Technique

  1. Remove the pen from the refrigerator and allow it to reach room temperature (approximately 30 minutes)
  2. Inspect the solution: it should be clear, colorless to slightly yellow, and free of particulate matter
  3. Clean the injection site (abdomen, thigh, or upper arm) with an alcohol swab
  4. Remove the pen cap and place the flat base firmly against the skin
  5. Unlock and press the injection button; hold for 10 seconds until the confirmation sound
  6. Dispose of the used pen in a sharps container

Compounded Tirzepatide

Some 503A and 503B compounding pharmacies produce tirzepatide in lyophilized vial or solution form. Compounded versions require reconstitution (if lyophilized) and accurate dose measurement with an insulin syringe. Patients using compounded tirzepatide should work with their prescriber to determine proper reconstitution volume and syringe graduations.

Side Effects

Common Adverse Reactions (≥5% incidence)

Adverse Event Incidence (5 mg) Incidence (10 mg) Incidence (15 mg)
Nausea 12 – 18% 15 – 22% 18 – 24%
Diarrhea 12 – 15% 13 – 17% 14 – 17%
Decreased appetite 5 – 9% 7 – 11% 9 – 14%
Vomiting 4 – 6% 5 – 9% 6 – 10%
Constipation 5 – 7% 5 – 7% 5 – 8%
Dyspepsia 5 – 8% 5 – 8% 5 – 8%
Injection site reactions 3 – 5% 3 – 6% 4 – 7%

Serious Adverse Reactions (Rare)

  • Pancreatitis: Acute pancreatitis has been reported. Discontinue if pancreatitis is suspected. Do not restart if confirmed.[15]
  • Gallbladder events: Cholelithiasis and cholecystitis have been reported at higher rates than placebo, consistent with the rapid weight loss effect.[5]
  • Hypoglycemia: Risk is increased when used with sulfonylureas or insulin. Serious hypoglycemia is uncommon when used as monotherapy or with metformin.[15]
  • Hypersensitivity reactions: Anaphylaxis and angioedema have been reported rarely.[15]
  • Acute kidney injury: Reported in the setting of dehydration from GI adverse effects, particularly in patients with pre-existing renal impairment.[15]
GI Tolerability

Gastrointestinal side effects are dose-dependent and most pronounced during dose escalation phases. Most GI symptoms are mild to moderate in severity and typically diminish within 2–4 weeks at each dose level. The 4-week titration intervals in the approved dosing schedule are specifically designed to improve GI tolerability.

Drug Interactions

Interacting Drug / Class Effect Recommendation
Sulfonylureas Increased hypoglycemia risk Reduce sulfonylurea dose when initiating tirzepatide
Insulin Increased hypoglycemia risk Reduce insulin dose; monitor blood glucose closely
Oral contraceptives Delayed gastric emptying may reduce absorption of oral hormonal contraceptives Switch to non-oral contraception or use barrier method for 4 weeks after initiation and each dose escalation
Oral medications with narrow therapeutic index Delayed absorption due to slowed gastric emptying Monitor drug levels; consider timing adjustments (warfarin, digoxin, levothyroxine)

Storage

  • Unopened pens: Refrigerate at 2–8°C (36–46°F). May be stored at room temperature (up to 30°C / 86°F) for up to 21 days. Protect from light.
  • Do not freeze. Discard if the pen has been frozen.
  • Protect from direct sunlight and heat.
  • Compounded vials (reconstituted): Refrigerate and use within 21 days; follow compounding pharmacy guidance.

Open Questions

  • Long-term cardiovascular outcomes: The dedicated SURPASS-CVOT trial is evaluating major adverse cardiovascular events (MACE) outcomes with tirzepatide. Results are anticipated but not yet published as of April 2026.
  • Weight regain upon cessation: SURMOUNT-4 demonstrated significant weight regain after discontinuation. The optimal duration of therapy and strategies for weight maintenance remain unclear.[14]
  • Lean mass preservation: Approximately 25–40% of weight lost with GLP-1/GIP agonists may be lean body mass. The long-term metabolic and musculoskeletal consequences require further study.
  • Thyroid cancer risk in humans: The boxed warning is based on rodent C-cell tumor findings. Long-term human epidemiologic data are needed to clarify actual risk.
  • Combination with retatrutide or other multi-receptor agonists: The role of triple agonism (GIP/GLP-1/glucagon) versus dual agonism is under active investigation.
  • Pediatric use: Safety and efficacy in patients under 18 have not been established.

Bibliography

  1. Frias JP, Davies MJ, Rosenstock J, et al. Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes. N Engl J Med. 2021;385(6):503-515. doi:10.1056/NEJMoa2107519 · PubMed 34170647
  2. Coskun T, Sloop KW, Loghin C, et al. LY3298176, a novel dual GIP and GLP-1 receptor agonist for the treatment of type 2 diabetes mellitus: from discovery to clinical proof of concept. Mol Metab. 2018;18:3-14. doi:10.1016/j.molmet.2018.09.009 · PubMed 30473097
  3. Nauck MA, Meier JJ. Incretin hormones: their role in health and disease. Diabetes Obes Metab. 2018;20(Suppl 1):5-21. doi:10.1111/dom.13129 · PubMed 29364588
  4. Willard FS, Douros JD, Gabe MB, et al. Tirzepatide is an imbalanced and biased dual GIP and GLP-1 receptor agonist. JCI Insight. 2020;5(17):e140532. doi:10.1172/jci.insight.140532 · PubMed 32730231
  5. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(4):327-340. doi:10.1056/NEJMoa2206038 · PubMed 35658024
  6. Samms RJ, Coghlan MP, Sloop KW. How may GIP enhance the therapeutic efficacy of GLP-1? Trends Endocrinol Metab. 2020;31(6):410-421. doi:10.1016/j.tem.2020.02.006 · PubMed 32396843
  7. Fisman EZ, Tenenbaum A. The dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist tirzepatide: a novel cardiometabolic therapeutic prospect. Cardiovasc Diabetol. 2021;20(1):225. doi:10.1186/s12933-021-01412-5 · PubMed 34819089
  8. Rosenstock J, Wysham C, Frias JP, et al. Efficacy and safety of a novel dual GIP and GLP-1 receptor agonist tirzepatide in patients with type 2 diabetes (SURPASS-1): a double-blind, randomised, phase 3 trial. Lancet. 2021;398(10295):143-155. doi:10.1016/S0140-6736(21)01324-6 · PubMed 34186022
  9. Ludvik B, Giorgino F, Jodar E, et al. Once-weekly tirzepatide versus once-daily insulin degludec as add-on to metformin with or without SGLT2 inhibitors in patients with type 2 diabetes (SURPASS-3): a randomised, open-label, parallel-group, phase 3 trial. Lancet. 2021;398(10300):583-598. doi:10.1016/S0140-6736(21)01443-4 · PubMed 34370970
  10. Del Prato S, Kahn SE, Pavo I, et al. Tirzepatide versus insulin glargine in type 2 diabetes and increased cardiovascular risk (SURPASS-4): a randomised, open-label, parallel-group, multicentre, phase 3 trial. Lancet. 2021;398(10313):1811-1824. doi:10.1016/S0140-6736(21)02188-7 · PubMed 34672967
  11. Dahl D, Onishi Y, Norwood P, et al. Effect of subcutaneous tirzepatide vs placebo added to titrated insulin glargine on glycemic control in patients with type 2 diabetes: the SURPASS-5 randomized clinical trial. JAMA. 2022;327(6):534-545. doi:10.1001/jama.2022.0078 · PubMed 35133415
  12. Garvey WT, Frias JP, Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2): a double-blind, randomised, multicentre, placebo-controlled, phase 3 trial. Lancet. 2023;402(10402):613-626. doi:10.1016/S0140-6736(23)01200-X · PubMed 37385275
  13. Wadden TA, Chao AM, Machineni S, et al. Tirzepatide after intensive lifestyle intervention in adults with overweight or obesity: the SURMOUNT-3 phase 3 trial. Nat Med. 2023;29(11):2909-2918. doi:10.1038/s41591-023-02597-w · PubMed 37840095
  14. Aronne LJ, Sattar N, Horn DB, et al. Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity: the SURMOUNT-4 randomized clinical trial. JAMA. 2024;331(1):38-48. doi:10.1001/jama.2023.24945 · PubMed 38078870
  15. U.S. Food and Drug Administration. Mounjaro (tirzepatide) prescribing information. Revised 2024. FDA Label
  16. U.S. Food and Drug Administration. Zepbound (tirzepatide) prescribing information. Approved November 2023. FDA Label