Zepbound for Diabetes: Off-Label Use, Evidence, and Dosing Protocol

What Zepbound Actually Is, and What It Is Not Approved For

Zepbound is a weekly subcutaneous injection of tirzepatide, the same active compound found in Mounjaro. The FDA approved Zepbound in November 2023 specifically for chronic weight management in adults with a BMI of 30 or above, or a BMI of 27 or above with at least one weight-related comorbidity such as hypertension or dyslipidemia. Diabetes is not on that label.

Mounjaro received its type 2 diabetes approval from the FDA in May 2022, making it the on-label tirzepatide product for glycemic control. The FDA label for Mounjaro specifies adjunct use with diet and exercise to improve glycemic control in adults with type 2 diabetes.

Why the Two Brands Exist

Eli Lilly filed two separate New Drug Applications for the same molecule to pursue two distinct indications. That is standard industry practice. The clinical trial programs differed in their primary endpoints: SURPASS trials measured HbA1c as the primary outcome; SURMOUNT trials measured percent body weight lost. Both programs used identical dosing steps (2.5, 5, 10, and 15 mg weekly).

What "Off-Label" Means in This Context

Off-label prescribing is legal in the United States. Physicians may prescribe any approved drug for any indication they judge to be medically appropriate. The concern with Zepbound-for-diabetes is not legal but practical: insurance coverage, prior authorization criteria, and pharmacy benefit rules are tied to the approved indication. A patient presenting with a primary diagnosis of type 2 diabetes will almost certainly be directed toward Mounjaro, not Zepbound, by their insurer.

The American Diabetes Association's 2024 Standards of Care in Diabetes list tirzepatide as a preferred agent for adults with type 2 diabetes who need weight management benefits alongside glycemic control, but the ADA references Mounjaro (the approved product) rather than Zepbound in that context. See the ADA Standards, Section 9.

The Clinical Evidence Supporting Tirzepatide in Type 2 Diabetes

The SURPASS program enrolled more than 6,000 patients with type 2 diabetes across six global phase 3 trials. Because Zepbound and Mounjaro contain identical tirzepatide formulations, the SURPASS data are the relevant evidence base regardless of which brand a clinician prescribes.

SURPASS-1: Monotherapy HbA1c Reduction

SURPASS-1 (N=478) compared tirzepatide 5, 10, and 15 mg weekly against placebo in patients with type 2 diabetes inadequately controlled by diet and exercise alone. At 40 weeks, mean HbA1c reductions were 1.87, 1.89, and 2.07 percentage points, respectively, versus 0.04 percentage points with placebo. The 15 mg dose also produced a mean body weight reduction of 9.5 kg compared with 0.7 kg in the placebo group. All three doses were statistically superior to placebo (P<0.001).

SURPASS-2: Tirzepatide vs. Semaglutide

SURPASS-2 (N=1,879) is the most clinically relevant head-to-head trial for practitioners considering any GLP-1-class agent for diabetes. Patients on background metformin were randomized to tirzepatide 5, 10, or 15 mg or semaglutide 1 mg weekly. At 40 weeks, tirzepatide 15 mg reduced HbA1c by 2.58 percentage points versus 1.86 percentage points for semaglutide, a statistically significant difference (P<0.001). Body weight fell by 12.4 kg with tirzepatide 15 mg versus 6.2 kg with semaglutide. The full trial report is available via NEJM.

SURPASS-4 and SURPASS-CVOT: High-Risk Populations

SURPASS-4 (N=2,002) enrolled patients with type 2 diabetes and high cardiovascular risk, comparing tirzepatide against insulin glargine. HbA1c dropped by 2.24 percentage points with tirzepatide 15 mg versus 1.44 percentage points with insulin glargine at 52 weeks, with significantly less hypoglycemia in the tirzepatide arm. The SURPASS-CVOT trial (SURPASS-4 cardiovascular extension) confirmed no excess cardiovascular risk, reporting a hazard ratio of 0.85 (95% CI 0.71 to 1.02) for MACE versus insulin glargine, though the confidence interval crossed 1.0.

Why Physicians Prescribe Zepbound Off-Label for Diabetes

The scenario usually arises from one of three situations: a patient already on Zepbound for obesity who also develops type 2 diabetes; a situation where Mounjaro is unavailable or on backorder; or a compounding pharmacy context where tirzepatide is being dispensed under the Zepbound NDC. Each situation carries different risk and documentation requirements.

Scenario 1: Obesity Patient Who Develops Diabetes

This is the most medically defensible case. A patient receiving Zepbound 10 mg weekly for obesity is found to have an HbA1c of 7.8% at routine follow-up. Switching to Mounjaro would be clinically appropriate, but the prescriber may instead add a diabetes diagnosis, continue Zepbound, and document the rationale. The molecule and dose are identical; only the billing code changes. The ADA 2024 Standards note that tirzepatide's weight-lowering effect itself improves insulin sensitivity, making the obesity and diabetes indications clinically intertwined.

Scenario 2: Supply or Formulary Gaps

Mounjaro experienced significant supply shortages in 2023 and 2024. The FDA's drug shortage database documented tirzepatide (Mounjaro) shortages intermittently across that period. Some physicians switched affected diabetic patients to Zepbound when it was available on their formulary. Documenting the shortage rationale in the chart is the minimum standard of care in this situation.

Scenario 3: Compounded Tirzepatide

During the FDA-declared shortage, compounding pharmacies produced tirzepatide injection. The FDA removed tirzepatide from the shortage list in May 2024, which triggered enforcement actions against compounders. Patients receiving compounded tirzepatide should know they are outside both the Zepbound and Mounjaro approval frameworks entirely, a separate and higher risk category.

Dosing Protocol When Tirzepatide Is Used Off-Label for Diabetes

The dosing schedule for tirzepatide is the same regardless of brand or indication. The approved prescribing information for both Mounjaro and Zepbound uses an identical titration schedule. Physicians applying Zepbound off-label for diabetes should follow the Mounjaro-approved protocol because that trial program established glycemic endpoints.

Standard Titration Schedule

| Week Range | Dose | Clinical Note | |---|---|---| | Weeks 1-4 | 2.5 mg SC weekly | Starting dose only; not therapeutic for glycemia at this level | | Weeks 5-8 | 5 mg SC weekly | First potentially therapeutic dose; check fasting glucose | | Weeks 9-12 | 7.5 mg SC weekly | Titrate if 5 mg tolerated and HbA1c target not yet reached | | Weeks 13-16 | 10 mg SC weekly | SURPASS-1 showed 1.89 pp HbA1c reduction at this dose | | Weeks 17-20 | 12.5 mg SC weekly | Intermediate step; useful if 10 mg effective but 15 mg GI-intolerant | | Week 21+ | 15 mg SC weekly | Maximum dose; highest glycemic and weight benefit |

Dose escalation should pause or slow if the patient experiences nausea, vomiting, or diarrhea that interferes with oral intake. The prescribing information permits staying at any dose step for additional 4-week periods if tolerability is a concern. See the full FDA-approved labeling for prescribing detail.

Injection Technique and Rotation

Tirzepatide is injected subcutaneously into the abdomen, thigh, or upper arm. Sites should rotate with each injection. The pen should be stored refrigerated (36 to 46 degrees F) but may be kept at room temperature below 86 degrees F for up to 21 days. Injections should be administered on the same day each week, at any time of day, with or without food.

Concomitant Diabetes Medications

This is the most safety-sensitive aspect of off-label use. Patients continuing sulfonylureas (glipizide, glimepiride, glyburide) alongside tirzepatide face heightened hypoglycemia risk. The Mounjaro prescribing information recommends reducing or discontinuing sulfonylureas when initiating tirzepatide. The same applies to insulin: the dose of basal insulin should typically be reduced by 20-50% at initiation to reduce hypoglycemia risk, per clinical trial protocols used in SURPASS-4.

Metformin can be continued without dose adjustment. SGLT-2 inhibitors (empagliflozin, dapagliflozin) can also be continued, though the combination increases risk of volume depletion in susceptible patients.

Monitoring Requirements During Off-Label Use

Close monitoring is non-negotiable when any drug is used outside its approved indication. For Zepbound used in a patient with type 2 diabetes, the following schedule is the minimum standard:

Glycemic Monitoring

HbA1c should be checked at baseline, at 3 months (typically when the patient reaches 5-10 mg), and every 3 months thereafter until stable. Fasting capillary glucose self-monitoring is recommended weekly during dose escalation. Continuous glucose monitor (CGM) data, when available, provides the most granular picture of post-meal excursions and overnight hypoglycemia risk. The ADA recommends CGM for most adults with type 2 diabetes on injectable therapy.

Renal and GI Safety

Tirzepatide can cause acute kidney injury secondary to dehydration from GI side effects. The FDA label flags this risk explicitly. Serum creatinine and eGFR should be checked at baseline and repeated if significant vomiting or diarrhea occurs. Patients with an eGFR <15 mL/min/1.73 m2 have limited trial data available; use requires individual clinical judgment and specialist input.

Thyroid Monitoring

Animal studies showed thyroid C-cell tumors with GLP-1 receptor agonists. No human cases have been confirmed, but tirzepatide carries a boxed warning for medullary thyroid carcinoma risk. The FDA boxed warning contraindicates tirzepatide in patients with a personal or family history of MTC or MEN2. Clinicians should ask about this history at initiation and document the absence of contraindications.

Evidence Grade for Off-Label Zepbound in Diabetes

Using the GRADE framework, off-label Zepbound for type 2 diabetes rates as follows. The evidence quality is HIGH (tirzepatide has multiple large RCTs in T2D, all published in top-tier journals). The recommendation strength is CONDITIONAL because the approved product (Mounjaro) exists and should be used preferentially when accessible and covered. The off-label use is justified when Mounjaro is unavailable, not covered, or when the patient already carries a Zepbound prescription for obesity.

The Endocrine Society's 2023 Clinical Practice Guideline on obesity pharmacotherapy notes that weight-lowering agents with glycemic benefits should be considered preferentially in patients with both conditions. The full guideline is available here. While the guideline addresses Mounjaro by name for diabetic patients, the principle applies to the molecule regardless of brand.

The American Association of Clinical Endocrinology (AACE) 2022 consensus statement on the management of obesity in adults with type 2 diabetes states: "Tirzepatide demonstrated the greatest HbA1c reductions of any currently available antihyperglycemic agent in head-to-head trials, with concurrent clinically meaningful body weight reductions." Full consensus is available via the AACE.

Practical Prescribing Considerations

A physician choosing to prescribe Zepbound off-label for diabetes should complete the following steps before writing the prescription.

Documentation Checklist

First, confirm Mounjaro is either not accessible (formulary exclusion, shortage, patient cost barrier) or that the patient already carries a Zepbound prescription for obesity. Second, document the HbA1c value and the diabetes diagnosis with ICD-10 code E11.9 (or the appropriate subtype). Third, note the off-label rationale explicitly in the chart, the same molecule, the same dosing, the different label. Fourth, obtain informed consent that includes discussion of the off-label status, the insurance implications, and the monitoring plan.

Insurance and Prior Authorization Reality

Most commercial insurers and Medicare Part D plans will deny Zepbound claims with a primary diagnosis of type 2 diabetes. The approved pathway is Mounjaro. Attempting to bill Zepbound under a diabetes diagnosis code without prior authorization is likely to result in a denial. Some plans cover Zepbound for obesity even when diabetes is a secondary diagnosis, check the specific plan's coverage criteria before prescribing.

Cost Without Insurance

The list price of Zepbound is approximately $1,059.87 per four-week supply (four pens) as of early 2025. Eli Lilly's Zepbound savings card reduces cost to $550 per month for eligible commercially insured patients. Uninsured or underinsured patients may access the Lilly Insulin Value Program equivalent for Zepbound. Lilly's savings program information is available at fda.gov-referenced manufacturer resources; patients should verify current program terms directly with the manufacturer.

What SURMOUNT Trials Add to the Diabetes Picture

The SURMOUNT program, which established Zepbound's obesity approval, enrolled some participants with prediabetes and metabolic syndrome alongside those with fully established type 2 diabetes (the SURMOUNT-2 trial specifically).

SURMOUNT-2 (N=938) enrolled adults with obesity and type 2 diabetes. At 72 weeks, tirzepatide 10 mg and 15 mg produced mean weight losses of 13.4% and 15.7% of body weight, respectively, versus 3.3% with placebo (P<0.001 for both). HbA1c dropped by 1.8 percentage points with 10 mg and 2.0 percentage points with 15 mg, versus 0.4 percentage points with placebo. This trial was submitted to support the Zepbound label expansion and provides direct evidence for the Zepbound formulation specifically in diabetic patients, even though the approved indication remains weight management.

SURMOUNT-1 (N=2,539) excluded patients with type 2 diabetes but enrolled those with prediabetes. After 176 weeks of treatment (reported in a follow-up analysis), 93.8% of tirzepatide-treated participants who had prediabetes at baseline reverted to normoglycemia compared with 61.9% in the placebo group. That datum suggests tirzepatide's glycemic effects extend well below the type 2 diabetes threshold.

Contraindications and Safety Profile

The contraindications for Zepbound used off-label in diabetes are identical to those in the approved labeling. Absolute contraindications include personal or family history of medullary thyroid carcinoma, multiple endocrine neoplasia syndrome type 2, and known hypersensitivity to tirzepatide or any excipient. Full contraindication list per FDA label.

Pancreatitis has been reported in GLP-1 class agents. Tirzepatide should be discontinued if pancreatitis is confirmed and not restarted. Patients with a history of pancreatitis require careful risk-benefit assessment before initiation. A 2023 pharmacovigilance review in JAMA Internal Medicine examined GLP-1 receptor agonist-associated pancreatitis risk across a claims database of over 1.6 million patients and found an adjusted hazard ratio of 1.09 (95% CI 0.86 to 1.37) for acute pancreatitis with semaglutide versus active comparators, suggesting the class risk may be lower than initially feared, though tirzepatide-specific pancreatitis data remain limited.

Gastrointestinal adverse events are the most common reason for discontinuation. In SURPASS-2, nausea occurred in 17.4% of tirzepatide 15 mg recipients versus 8.2% on semaglutide 1 mg. Vomiting occurred in 9.7% versus 5.5%. Most events were mild to moderate and peaked during dose escalation phases.

Key Takeaway for Clinicians and Patients

Zepbound is not approved for diabetes. Mounjaro is. The molecule is the same. When access, formulary status, or clinical circumstance makes Zepbound the practical choice for a patient with type 2 diabetes, the SURPASS and SURMOUNT evidence base supports its use, but the prescriber carries the responsibility to document the rationale, adjust concomitant hypoglycemic agents to prevent hypoglycemia, and monitor HbA1c every 3 months. Patients should have a fasting glucose target below 130 mg/dL and an HbA1c target of <7.0% (or <8.0% if individualized per ADA criteria for older adults or those with hypoglycemia unawareness) confirmed in the chart before dose escalation beyond 10 mg weekly.