Tirzepatide

Dosing from the Literature

Published for fat loss: Zepbound's 2.5 mg a week, raised in 2.5 mg steps to 5–15 mg, from the SURMOUNT trials. Not published: nothing missing; the dose is on the label.

Tirzepatide is an FDA-approved drug; the following reflects labeled prescribing in the United States. This does not substitute for a prescribing clinician's instructions.

What It Is

Tirzepatide is a first-in-class once-weekly synthetic peptide that activates both the glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor. It is a 39-amino-acid linear peptide engineered from the native GIP sequence, with non-proteinogenic aminoisobutyric acid (Aib) residues at positions 2 and 13 to protect against DPP-4 degradation, a C-terminal amide cap, and a C20 fatty diacid moiety covalently attached via a γGlu-2xOEG linker at Lys20. That fatty-acid tail enables reversible albumin binding, which is what drives the drug's ~5-day plasma half-life and supports once-weekly subcutaneous dosing (Coskun et al., Mol Metab 2018; PMID 30473097).

Tirzepatide is marketed as Mounjaro for type 2 diabetes (FDA approved May 13, 2022), as Zepbound for chronic weight management in adults with obesity or overweight with weight-related comorbidities (FDA approved November 8, 2023), and as Zepbound for moderate-to-severe obstructive sleep apnea in adults with obesity (FDA approved December 2024 on the basis of SURMOUNT-OSA). Both brands contain identical active ingredient — only labeling, dose range, and indication differ.

What separates tirzepatide from every selective GLP-1 agonist that preceded it is the GIP component. Native GIP signaling had historically been dismissed as a metabolic dead end — partially because GIP receptors are relatively desensitized in type 2 diabetes and partially because GIP elevation alone does not improve glycemia. The tirzepatide hypothesis was that co-activating both incretin receptors on the same molecule would produce synergistic — not merely additive — effects on insulin secretion, glucagon suppression, energy intake, and adipose tissue biology. Head-to-head data (SURPASS-2) and the obesity program (SURMOUNT-1 through SURMOUNT-4, plus SURMOUNT-OSA) have largely validated that hypothesis — tirzepatide produces the largest weight loss and the largest HbA1c reductions of any injectable incretin to date.

The drug's development trajectory has been unusually rapid: from first-in-human in 2016 to T2D approval in 2022 (6 years), then obesity expansion at 18 months, then OSA expansion at 12 more months. SUMMIT (HFpEF + obesity) was a positive Phase 3 trial (Packer et al., 2025; PMID 39555826); SYNERGY-NASH (MASH) was Phase 2 (Loomba et al., 2024; PMID 38856224), with the Phase 3 SYNERGY-Outcomes now recruiting (ClinicalTrials.gov NCT07165028); and SURPASS-CVOT, against dulaglutide, finished in 2025 and added a cardiovascular indication to the Mounjaro label in August 2026 (Mounjaro label). The cumulative Phase 3 patient exposure dwarfs almost any other peptide compound in recent pharmaceutical history.

Mechanism of Action

Tirzepatide is not a balanced dual agonist: in receptor-binding assays it binds the GIP receptor about as tightly as native GIP, but the GLP-1 receptor about 5-fold more weakly than native GLP-1. Its developers suggested this greater potency at the GIP receptor may partly explain its effects (Coskun et al., 2018; PMID 30473097).

• GLP-1 receptor activation (glucose-dependent insulin secretion) — Tirzepatide stimulates insulin secretion and lowers glucagon, both in a glucose-dependent manner (Mounjaro label); GLP-1 receptor agonists as a class also delay gastric transit and act on appetite pathways in the brain (Coskun et al., 2018; PMID 30473097). Because insulinotropic activity is glucose-dependent, intrinsic hypoglycemia risk is low (Coskun et al., 2018).
• GIP receptor activation (adipose biology + glucagon modulation) — GIP accounts for most of the insulin-releasing incretin effect in people; unlike GLP-1, it raises glucagon when blood glucose is low and insulin when it is high, and its receptor is abundant in fat tissue and found in brain areas distinct from GLP-1's (Coskun et al., 2018; PMID 30473097). In human fat cells, which carry only GIP receptors, tirzepatide raised cAMP as much as GIP did (Coskun et al., 2018). The labels say nonclinical studies suggest GIP may add to the regulation of food intake, and a 28-week clamp study in type 2 diabetes showed tirzepatide increases insulin sensitivity (Zepbound label).
• Gastric emptying (transient) — Tirzepatide delays gastric emptying; the delay is largest after the first dose and diminishes over time (Mounjaro and Zepbound labels). After a first 5 mg dose, peak levels of oral acetaminophen fell 55%, with no meaningful effect at week 6 on 15 mg (Zepbound label).
• Central appetite — GIP and GLP-1 receptors are both found in brain areas involved in appetite; in animal studies tirzepatide reached and activated neurons in regions that regulate appetite and food intake, and the labels attribute its lower calorie intake to effects on appetite (Zepbound label).
• Hepatic effects (MASH/NAFLD) — In SYNERGY-NASH Phase 2, tirzepatide achieved MASH resolution without fibrosis worsening in 44–62% of participants across doses vs 10% placebo (Loomba et al., NEJM 2024; PMID 38856224).
• Cardio-renal effects — SURPASS-4 post-hoc analysis: slowed eGFR decline and reduced new-onset macroalbuminuria vs insulin glargine (Heerspink et al., Lancet Diabetes Endocrinol 2022; PMID 36152639). SUMMIT: 38% reduction in composite CV death / worsening HF in HFpEF + obesity (Packer et al., NEJM 2025; PMID 39555826).

What the Research Shows

Tirzepatide has the strongest human-efficacy evidence base of any compound on this site. The SURPASS (T2D), SURMOUNT (obesity), SURMOUNT-OSA (sleep apnea), SYNERGY-NASH (MASH), and SUMMIT (HFpEF + obesity) programs together enrolled tens of thousands of patients across global Phase 2 and Phase 3 trials.

• SURPASS-1 (Rosenstock 2021; PMID 34186022) — Drug-naïve T2D, 40 weeks. HbA1c reductions 1.87–2.07% across 5/10/15 mg vs –0.04% placebo; 88% of 15 mg patients reached HbA1c <7%; weight loss 7.0–9.5 kg.
• SURPASS-2 (Frías 2021; PMID 34170647) — Head-to-head vs semaglutide 1 mg on background metformin, 40 weeks. Tirzepatide 5/10/15 mg: HbA1c –2.01/–2.24/–2.30% vs –1.86% semaglutide; weight loss 7.6/9.3/11.2 kg vs 5.7 kg. Superiority on both endpoints at all doses.
• SURPASS-3, -4, -5 — vs insulin degludec (PMID 34370970), vs insulin glargine in high CV-risk T2D (PMID 34672967), added to glargine (PMID 35133415). Tirzepatide outperformed basal insulins on HbA1c and weight with favorable hypoglycemia profile.
• SURMOUNT-1 (Jastreboff 2022; PMID 35658024) — 72 weeks, 2,539 adults with obesity without diabetes. Mean weight loss: –15.0% (5 mg), –19.5% (10 mg), –20.9% (15 mg) vs –3.1% placebo. 57% of 15 mg participants lost ≥20%; 36% lost ≥25%.
• SURMOUNT-2 (Garvey 2023; PMID 37385275) — 72 weeks, obesity + T2D. Weight loss 13.4% (10 mg) / 15.7% (15 mg) vs 3.3% placebo.
• SURMOUNT-4 withdrawal (Aronne 2024; PMID 38078870) — 36-week lead-in then randomization to continue or placebo. Continued arm lost additional 5.5%; placebo regained 14%. Confirms maintenance therapy paradigm.
• SURMOUNT-1 3-yr prediabetes (Jastreboff 2025; PMID 39536238) — Sustained weight loss over 3 years; ~93% reduction in progression to T2D vs placebo.
• SURMOUNT-OSA (Malhotra 2024; PMID 38912654) — 52 weeks in moderate-to-severe OSA + obesity. AHI reduction 27.4–30.4 events/hr; basis for FDA OSA indication December 2024.
• SYNERGY-NASH (Loomba 2024; PMID 38856224) — 52-week Phase 2 in biopsy-confirmed MASH with F2/F3 fibrosis. MASH resolution without fibrosis worsening 44/56/62% (5/10/15 mg) vs 10% placebo.
• SUMMIT (Packer 2025; PMID 39555826) — 731 patients with obesity-related HFpEF. Primary composite (CV death or worsening HF event) reduced ~38% over median 104-week follow-up. KCCQ-CSS improved substantially; 6-MWD improved ~18 m vs placebo. CMR substudy showed reductions in LV mass and paracardiac adipose (Kramer et al., 2025).

Human Data

Tirzepatide's human dataset is among the largest in modern peptide pharmaceutical development:

• SURPASS program (T2D) — SURPASS-1 through SURPASS-5 + SURPASS J-mono + SURPASS J-combo. N > 6,000. NCT03954834, NCT03987919, NCT03882970, NCT03730662, NCT04039503.
• SURMOUNT program (obesity) — SURMOUNT-1 through SURMOUNT-5. N > 5,000. NCT04184622, NCT04657003, NCT04657016, NCT04660643, NCT05822830.
• SURMOUNT-OSA — NCT05412004. One master protocol with two trials, in adults not using and using positive airway pressure (PAP) therapy at baseline (Malhotra et al., 2024); the label reports the two trials separately as the basis of the OSA indication (Zepbound label).
• SYNERGY-NASH — NCT04166773. Phase 2 histologic endpoint; Phase 3 program in development.
• SUMMIT — NCT04847557. HFpEF + obesity. Positive for clinical and imaging endpoints.
• SURPASS-CVOT — NCT04255433. Dedicated CV outcomes trial vs dulaglutide 1.5 mg in 13,299 adults with T2D and established CVD; completed June 2025 (ClinicalTrials.gov). Over a median of about four years, tirzepatide was non-inferior to dulaglutide for CV death, heart attack or stroke (HR 0.92, 95.3% CI 0.83–1.01); superiority was not shown (Mounjaro label).
• Pharmacokinetics — Half-life ~5 days; steady-state at 4 weeks; exposure ~2× higher in obesity doses. Dose adjustment not required for renal or hepatic impairment (Urva et al., 2021, 2022; Schneck & Urva, 2024).

Reconstitution & Storage

Branded tirzepatide (Mounjaro / Zepbound) is supplied ready to inject, as a solution in single-dose pens and vials and in four-dose multi-dose vials and KwikPens — no reconstitution required (Mounjaro and Zepbound labels). One compounding seller's listing describes its tirzepatide as a solution dispensed in multi-dose vials, and also gives handling for freeze-dried powder mixed with bacteriostatic water; legal compounded supply has narrowed since FDA resolved the tirzepatide shortage in late 2024.

• Injection site rotation — The labels list the abdomen or thigh, or the back of the upper arm when another person gives the injection, with the site rotated each dose; the KwikPen instructions add at least 2 inches from the belly button (Mounjaro and Zepbound labels).
• Warming — The single-dose pen instructions say it is not necessary to warm the pen to room temperature before injecting (Mounjaro and Zepbound labels).
• Inspection — The labels describe a clear, colorless to slightly yellow solution, and the instructions list cloudiness, particles, discoloration or freezing as reasons not to use it (Mounjaro and Zepbound labels).
• Needle — The single-dose pens come with the needle in place under a base cap; the KwikPen takes a new pen needle for each dose, and the vials a new syringe and needle each time, such as a 1 mL syringe that can measure a 0.5 mL or 0.6 mL dose (Mounjaro and Zepbound labels). One seller's dosing guide for compounded vials measures doses with U-100 insulin syringes.

→ Calculator — vial-to-syringe math

Side Effects & Risks

In the SURPASS trials, tirzepatide's safety profile was consistent with the GLP-1 receptor agonist class (Rosenstock et al., 2021; Ludvik et al., 2021); the labels carry one boxed warning.

• Gastrointestinal (most common) — In the two weight-loss trials behind the Zepbound label, stomach and bowel side effects occurred in 56% of people on each dose vs 30% on placebo: nausea 25–29% (placebo 8%), diarrhea 19–23% (8%), vomiting 8–13% (2%), constipation 11–17% (5%), abdominal pain 9–10% (5%) and dyspepsia 9–10% (4%). Most nausea, vomiting and diarrhea came during dose escalation and decreased over time (Zepbound label); most events were mild to moderate (Jastreboff et al., 2022).
• Boxed warning — thyroid C-cell tumors — In rats, tirzepatide causes dose- and treatment-duration-dependent thyroid C-cell tumors at clinically relevant exposures; whether it causes them in humans is unknown. It is contraindicated in people with a personal or family history of medullary thyroid carcinoma (MTC) or with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2) (Mounjaro and Zepbound labels).
• Pancreatitis — Acute pancreatitis, including fatal hemorrhagic or necrotizing cases, has been seen with GLP-1 receptor agonists and with tirzepatide. In the type 2 diabetes trials it was confirmed in 13 people on tirzepatide (0.23 per 100 patient-years) vs 3 on comparators (0.11); in the weight-loss trials, in 0.2% on tirzepatide and 0.2% on placebo. The labels direct stopping the drug if pancreatitis is suspected (Mounjaro and Zepbound labels).
• Gallbladder disease — The labels link tirzepatide and GLP-1 receptor agonists to more acute gallbladder disease. In the two weight-loss trials, cholecystitis was reported in 0.7% vs 0.2% on placebo, cholelithiasis in 1.1% vs 1%, and gallbladder removal in 0.2% vs none; the events were associated with weight reduction (Zepbound label).
• Gastroparesis / delayed gastric emptying — Severe gastrointestinal reactions were reported in 1.7–3.1% of people in the weight-loss trials vs 1% on placebo, the labels do not recommend tirzepatide in severe gastroparesis, and postmarketing reports include ileus and intestinal obstruction. Because it delays gastric emptying, the labels also note rare postmarketing reports of pulmonary aspiration under general anesthesia or deep sedation with GLP-1 receptor agonists, and say the data are insufficient to tell whether changing pre-procedure fasting or pausing the drug lowers that risk (Mounjaro and Zepbound labels).
• Hypoglycemia — With tirzepatide alone, SURPASS-1 reported no clinically significant or severe hypoglycemia (Rosenstock et al., 2021). The risk rises with insulin or a sulfonylurea: in SURMOUNT-2, blood glucose below 54 mg/dL occurred in 10.3% of people on tirzepatide who also took a sulfonylurea vs 2.1% of those who did not, and the labels note that lowering the insulin or sulfonylurea dose may reduce the risk (Zepbound label).
• Acute kidney injury — The labels list postmarketing reports of acute kidney injury, in some cases needing dialysis, mostly in people dehydrated by nausea, vomiting or diarrhea, and call for monitoring kidney function in people with side effects that could deplete fluids, especially while the dose is started and raised. In the weight-loss trials it was reported in 0.5% vs 0.2% on placebo (Zepbound label).
• Injection-site reactions — Bruising, redness, itching, pain or rash at the injection site were reported in 6–8% of people in the weight-loss trials vs 2% on placebo, more often in those who developed antibodies to tirzepatide (Zepbound label).
• Suicidal ideation / mood — After postmarketing reports, FDA reviewed the GLP-1 drugs; its meta-analysis of 91 placebo-controlled trials with 107,910 patients found no increased risk of suicidal thoughts or behavior, or of depression or anxiety, and at FDA's request the Zepbound label dropped that warning in February 2026 (FDA Drug Safety Communication, January 13, 2026; Zepbound label).
• Lean mass loss — Weight lost on tirzepatide includes lean mass, though more fat than lean mass is lost (Zepbound label).
• Pregnancy + oral contraceptives — Tirzepatide may make oral hormonal contraceptives less effective by delaying gastric emptying, and the labels advise switching to a non-oral method, or adding a barrier method, for 4 weeks after starting and after each dose increase. The Zepbound label says weight loss offers no benefit in pregnancy and to stop the drug when pregnancy is recognized; the Mounjaro label limits use in pregnancy to when the potential benefit justifies the potential risk to the fetus. In a lactation study, tirzepatide in breast milk was undetectable or low (Mounjaro and Zepbound labels).
• Diabetic retinopathy — The labels report temporary worsening of diabetic retinopathy with rapid improvement in glucose control, and call for monitoring people with a history of retinopathy for progression (Mounjaro and Zepbound labels).

Bloodwork & Monitoring

Neither label sets a routine lab schedule. What the labels list, and what the trials measured:

• HbA1c + fasting glucose — In people with diabetes, the Zepbound label calls for monitoring blood glucose before starting and during treatment. In SURMOUNT-2, in adults with type 2 diabetes and overweight or obesity, HbA1c fell 2.1 points at 72 weeks vs 0.5 on placebo (Zepbound label).
• Kidney function — The labels call for monitoring kidney function in people with side effects that could deplete fluids, such as vomiting or diarrhea, especially while the dose is started and raised (Mounjaro and Zepbound labels). SURPASS-4 tracked eGFR and urine albumin-to-creatinine ratio (Heerspink et al., 2022).
• Lipid panel — In SURMOUNT-1, at 72 weeks triglycerides fell 21–29% vs 6% on placebo, non-HDL cholesterol 8–12% vs 2% and LDL cholesterol 5–7% vs 2%, while HDL cholesterol rose 7–9% vs a 1% fall on placebo; these were not formally tested end points (Zepbound label).
• Lipase / amylase — In the weight-loss trials, pancreatic amylase rose 20–25% and lipase 28–35% on average from baseline, vs 2% and 6% on placebo; the label calls their significance unknown without other signs of pancreatitis (Zepbound label).
• Blood pressure + heart rate — In SURMOUNT-1, systolic blood pressure fell 6.6–7.7 mmHg at 72 weeks vs 1.0 on placebo; in the two weight-loss trials, heart rate rose 1–3 beats per minute on average vs no rise on placebo (Zepbound label).
• Thyroid — The labels call routine calcitonin or thyroid ultrasound monitoring of uncertain value for finding medullary thyroid cancer early, and list a neck mass, trouble swallowing, shortness of breath or persistent hoarseness as possible symptoms of thyroid tumors (Mounjaro and Zepbound labels).

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References

1. Coskun T, Sloop KW, Loghin C, Alsina-Fernandez J, Urva S, Bokvist KB, 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. PMID: 30473097.
2. Jastreboff AM, Aronne LJ, Ahmad NN, Wharton S, Connery L, Alves B, et al.; SURMOUNT-1 Investigators. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022;387(3):205-216. PMID: 35658024.
3. Jastreboff AM, le Roux CW, Stefanski A, Aronne LJ, Halpern B, Wharton S, et al.; SURMOUNT-1 Investigators. Tirzepatide for Obesity Treatment and Diabetes Prevention. N Engl J Med. 2025;392(10):958-971. PMID: 39536238.
4. Frías JP, Davies MJ, Rosenstock J, Pérez Manghi FC, Fernández Landó L, Bergman BK, et al.; SURPASS-2 Investigators. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes. N Engl J Med. 2021;385(6):503-515. PMID: 34170647.
5. Rosenstock J, Wysham C, Frías JP, Kaneko S, Lee CJ, Fernández Landó L, et al.; SURPASS-1 Investigators. 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. PMID: 34186022.
6. Ludvik B, Giorgino F, Jódar E, Frias JP, Fernández Landó L, Brown K, 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. PMID: 34370970.
7. Del Prato S, Kahn SE, Pavo I, Weerakkody GJ, Yang Z, Doupis J, et al.; SURPASS-4 Investigators. 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. PMID: 34672967.
8. Dahl D, Onishi Y, Norwood P, Huh R, Bray R, Patel H, Rodríguez Á. 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. PMID: 35133415.
9. Garvey WT, Frias JP, Jastreboff AM, le Roux CW, Sattar N, Aizenberg D, et al.; SURMOUNT-2 Investigators. Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2). Lancet. 2023;402(10402):613-626. PMID: 37385275.
10. Aronne LJ, Sattar N, Horn DB, Bays HE, Wharton S, Lin WY, et al.; SURMOUNT-4 Investigators. 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. PMID: 38078870.
11. Malhotra A, Grunstein RR, Fietze I, Weaver TE, Redline S, Azarbarzin A, et al.; SURMOUNT-OSA Investigators. Tirzepatide for the Treatment of Obstructive Sleep Apnea and Obesity. N Engl J Med. 2024;391(13):1193-1205. PMID: 38912654.
12. Loomba R, Hartman ML, Lawitz EJ, Vuppalanchi R, Boursier J, Bugianesi E, et al.; SYNERGY-NASH Investigators. Tirzepatide for Metabolic Dysfunction-Associated Steatohepatitis with Liver Fibrosis. N Engl J Med. 2024;391(4):299-310. PMID: 38856224.
13. Packer M, Zile MR, Kramer CM, Baum SJ, Hurt K, Litwin SE, et al.; SUMMIT Trial Study Group. Tirzepatide for Heart Failure with Preserved Ejection Fraction and Obesity. N Engl J Med. 2025. PMID: 39555826.
14. Heerspink HJL, Sattar N, Pavo I, Haupt A, Duffin KL, Yang Z, et al. Effects of tirzepatide versus insulin glargine on kidney outcomes in type 2 diabetes in the SURPASS-4 trial: post-hoc analysis of an open-label, randomised, phase 3 trial. Lancet Diabetes Endocrinol. 2022;10(11):774-785. PMID: 36152639.
15. Schneck K, Urva S. Population pharmacokinetics of the GIP/GLP receptor agonist tirzepatide. CPT Pharmacometrics Syst Pharmacol. 2024;13:494-503. PMID: 38356317.
16. Urva S, Quinlan T, Landry J, Ma X, Martin JA, Benson CT. Effects of hepatic impairment on the pharmacokinetics of the dual GIP and GLP-1 receptor agonist tirzepatide. Clin Pharmacokinet. 2022;61(7):1057-1067. PMID: 35674880.
17. Urva S, Quinlan T, Landry J, Martin J, Loghin C. Effects of Renal Impairment on the Pharmacokinetics of the Dual GIP and GLP-1 Receptor Agonist Tirzepatide. Clin Pharmacokinet. 2021;60(8):1049-1059. PMID: 33778934.
18. U.S. Food and Drug Administration. FDA Approves New Medication for Chronic Weight Management (Zepbound). fda.gov. November 8, 2023.
19. Eli Lilly and Company. Mounjaro (tirzepatide) and Zepbound (tirzepatide) Prescribing Information. 2024.
20. FDA. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the FD&C Act (503A categories list), versions updated April 15, April 22 and May 14, 2026. fda.gov/media/94155/download. Read October 3, 2026. (Notice that 12 peptides would leave Category 2 because their nominations were withdrawn; their removal; GHK-Cu, except injectable, back in Category 1.)
21. FDA. List of Bulk Drug Substances for Which There Is a Clinical Need Under Section 503B of the Federal Food, Drug, and Cosmetic Act (notice). Federal Register, 91 FR 23431–23444, May 1, 2026; FR Doc. 2026-08552; Docket No. FDA-2018-N-3240. federalregister.gov/documents/2026/05/01/2026-08552/list-of-bulk-drug-substances-for-which-there-is-a-clinical-need-under-section-503b-of-the-federal. Comment period extended to July 30, 2026: 91 FR 38719, June 26, 2026; FR Doc. 2026-12937. Read October 3, 2026. (Proposes not to include semaglutide, tirzepatide and liraglutide on the 503B bulks list; lists the approved tirzepatide pens and vials, including four-dose KwikPens and vials, and the December 19, 2025 approval for children 10 and older.)
22. Eli Lilly and Company. Mounjaro (tirzepatide) injection prescribing information. DailyMed set ID d2d7da5d-ad07-4228-955f-cf7e355c8cc0 (version effective August 27, 2026). dailymed.nlm.nih.gov. Read October 3, 2026.
23. Eli Lilly and Company. Zepbound (tirzepatide) injection prescribing information. DailyMed set ID 487cd7e7-434c-4925-99fa-aa80b1cc776b (version effective August 28, 2026). dailymed.nlm.nih.gov. Read October 3, 2026.
24. Aronne LJ, Horn DB, le Roux CW, Ho W, Falcon BL, Gomez Valderas E, et al.; SURMOUNT-5 Trial Investigators. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity. N Engl J Med. 2025;393(1):26-36. PMID: 40353578.
25. Petersen J, Merrild C, Holm SK, Kurgan N, Hassan S, Mathiesen CV, et al. Cagrilintide and retatrutide combination therapy enhances weight loss and metabolic outcomes in obese male rats. Nat Metab. 2026. PMID: 42744908.
26. Kramer CM, Borlaug BA, Zile MR, et al.; SUMMIT Trial Study Group. Tirzepatide Reduces LV Mass and Paracardiac Adipose Tissue in Obesity-Related Heart Failure: SUMMIT CMR Substudy. J Am Coll Cardiol. 2025;85(7):699-706. PMID: 39566869. DOI: 10.1016/j.jacc.2024.11.001.

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