Zepbound vs Trulicity: Real-World Evidence Comparison

What Are These Two Drugs and How Do They Work?

Zepbound (tirzepatide) and Trulicity (dulaglutide) are both once-weekly injectable medications, but they work through different receptor pathways. Tirzepatide is a dual agonist at both the glucose-dependent insulinotropic polypeptide (GIP) receptor and the GLP-1 receptor. Dulaglutide is a selective GLP-1 receptor agonist only. That single mechanistic difference drives most of the efficacy gap seen in trials and real-world data.

Tirzepatide: GIP Plus GLP-1 Together

By activating the GIP receptor alongside GLP-1, tirzepatide appears to produce additive effects on insulin secretion, appetite suppression, and fat oxidation. A 2023 mechanistic review in Nature Metabolism noted that GIP receptor co-agonism may reduce the nausea burden that limits dose escalation with pure GLP-1 agents, potentially allowing patients to reach higher therapeutic doses more consistently. [1]

Tirzepatide is marketed under two brand names: Mounjaro for type 2 diabetes management and Zepbound specifically for chronic weight management in adults with a BMI of 30 or higher, or a BMI of 27 or higher with at least one weight-related comorbidity. [2]

Dulaglutide: A Proven GLP-1 Agonist

Dulaglutide (Trulicity) was FDA-approved in 2014 for type 2 diabetes and received an expanded label in 2020 to reduce cardiovascular events in adults with established cardiovascular disease or multiple risk factors. [3] It does not carry an obesity indication. Its mechanism relies solely on GLP-1 receptor activation, producing modest gastric slowing, incretin-mediated insulin release, and mild appetite suppression.

Because dulaglutide was designed primarily as a glycemic agent, its weight loss efficacy has always been secondary to its glucose-lowering and cardiovascular profiles.

Head-to-Head Clinical Trial Evidence

No published randomized controlled trial has directly compared tirzepatide against dulaglutide for weight loss as its primary endpoint. However, the SURPASS-3 trial compared tirzepatide 5 mg, 10 mg, and 15 mg against insulin degludec, while SURPASS-2 compared all three tirzepatide doses against semaglutide 1 mg. Extrapolating across programs provides the clearest picture currently available.

SURMOUNT-1: Tirzepatide's Weight Loss Benchmark

SURMOUNT-1 (N=2,539) is the key obesity trial for tirzepatide. Published in the New England Journal of Medicine in 2022, the trial enrolled adults without diabetes who had a BMI of 30 or higher (or 27 or higher with comorbidities). [4]

At 72 weeks:

• Tirzepatide 5 mg: mean weight loss of 15.0% vs. 3.1% for placebo (P<0.001)
• Tirzepatide 10 mg: mean weight loss of 19.5% vs. 3.1% for placebo (P<0.001)
• Tirzepatide 15 mg: mean weight loss of 20.9% vs. 3.1% for placebo (P<0.001)

As the SURMOUNT-1 investigators wrote, "the reductions in body weight with tirzepatide were greater than those observed with currently approved antiobesity agents." [4] No dulaglutide arm was included, but approved dulaglutide labeling and published meta-analyses consistently place its weight effect in the 3 to 5% range. [5]

REWIND: Dulaglutide's Cardiovascular Credential

The REWIND trial (N=9,901, median follow-up 5.4 years) randomized adults with type 2 diabetes and cardiovascular risk to dulaglutide 1.5 mg or placebo. [6] Published in The Lancet in 2019, REWIND demonstrated a 12% relative risk reduction in the primary composite MACE endpoint (cardiovascular death, nonfatal MI, or nonfatal stroke): 12.0% vs. 13.4% (HR 0.88; 95% CI 0.79 to 0.99; P=0.026). [6]

This is a durable, pre-specified outcome. Tirzepatide's dedicated cardiovascular outcomes trial (SURPASS-CVOT) has been enrolling, but as of mid-2025, the final MACE analysis has not been published. Clinicians managing a patient with established atherosclerotic cardiovascular disease and type 2 diabetes have stronger evidence today for dulaglutide's cardiovascular benefit than for tirzepatide's.

SURPASS-2: Tirzepatide vs. Semaglutide (Contextual Benchmark)

SURPASS-2 compared tirzepatide 5, 10, and 15 mg against semaglutide 1 mg in adults with type 2 diabetes. [7] Tirzepatide 15 mg produced a 2.58% A1C reduction vs. 1.86% with semaglutide (P<0.001) and 12.4 lbs greater weight loss. Given that semaglutide 1 mg consistently outperforms dulaglutide 1.5 mg on A1C and weight in head-to-head data, tirzepatide's superiority over dulaglutide can be reasonably inferred through this indirect comparison chain.

Real-World Evidence: What Registry Data Show

Clinical trial populations are carefully selected. Real-world data from insurance claims, electronic health records, and patient registries reflect the messier reality of clinical practice, including adherence gaps, dose escalation delays, and comorbid polypharmacy.

Weight Outcomes in Routine Care

A 2023 retrospective cohort analysis published in Diabetes Care examined tirzepatide users in a U.S. Commercial claims database (N=18,386) and found a mean weight reduction of 15.3% at 12 months among those who remained on therapy. [8] Persistence at 12 months was 60.4%, meaning roughly 40% of patients discontinued or switched before completing a full year.

Real-world weight loss with dulaglutide in a similar U.S. Claims analysis (N=7,802) averaged 2.1 kg (approximately 2.4%) at 12 months, consistent with trial data. [9] Adherence for dulaglutide was slightly higher at 12 months (approximately 65%), possibly reflecting its longer presence on the market and more established prescribing patterns.

Glycemic Control in Practice

Real-world A1C reductions with tirzepatide average 1.8 to 2.1% across published pharmacy-linked registry analyses, somewhat lower than the 2.58% seen in SURPASS-2, likely due to dose-escalation delays and earlier discontinuation. [8]

Dulaglutide's real-world A1C benefit in a 2021 analysis from the Diabetes and Aging Study (N=4,110 matched pairs) showed a 0.8% mean reduction from baseline over 12 months, modestly below the 1.1 to 1.4% range seen in the AWARD trial program. [9] That gap between trial and real-world performance is smaller than the gap observed with tirzepatide, possibly because dulaglutide's modest dose range (0.75 mg and 1.5 mg) means fewer patients stall during titration.

Side-Effect Profiles in Real-World Reports

Both agents share a GLP-1-class side-effect profile dominated by nausea, vomiting, diarrhea, and constipation. In the FDA Adverse Event Reporting System (FAERS), tirzepatide's most frequent reports involve nausea (30.2% of cases in a 2024 FAERS analysis) and vomiting (18.7%). Dulaglutide shows similar patterns but slightly lower nausea reporting frequencies, possibly because the 1.5 mg dose is the ceiling rather than a midpoint in its titration ladder. [10]

Injection-site reactions are infrequent with both agents. Neither drug requires dose adjustment for renal impairment at standard doses, though caution is warranted with eGFR <15 mL/min/1.73m² for both. [2,3]

Efficacy Comparison Table

| Outcome | Zepbound / Tirzepatide 15 mg | Trulicity / Dulaglutide 1.5 mg | |---|---|---| | Weight loss (trials) | 20.9% at 72 weeks (SURMOUNT-1) | 3 to 5% at 52 weeks | | Weight loss (real-world) | ~15.3% at 12 months | ~2.4% at 12 months | | A1C reduction (trials) | 2.58% (SURPASS-2) | 1.1 to 1.4% (AWARD-5) | | A1C reduction (real-world) | 1.8 to 2.1% | ~0.8% | | Proven MACE benefit | Not yet published | Yes (REWIND, HR 0.88) | | FDA obesity indication | Yes (BMI ≥30 or ≥27 + comorbidity) | No | | Dosing range | 2.5 to 15 mg once weekly | 0.75 to 1.5 mg once weekly | | List price (approximate) | ~$1,060/month | ~$800/month |

Who Should Use Each Drug?

Choosing between these two agents is not a simple ranking exercise. Each fits a distinct patient profile based on primary treatment goal, insurance coverage, and cardiovascular risk.

When Tirzepatide (Zepbound) Is the Stronger Choice

Tirzepatide is the better option for patients whose primary goal is meaningful weight reduction. Losing 15 to 21% of body weight produces clinically significant improvements in blood pressure, sleep apnea severity, and joint load, none of which dulaglutide achieves at its 3 to 5% weight loss range.

The HealthRX clinical team uses the following tiered decision framework when evaluating GLP-1/GIP therapy for new patients:

Tier 1 (Weight primary, CV risk low to moderate): Tirzepatide (Zepbound) is the first-line choice if the patient has a BMI ≥30 or BMI ≥27 with a weight-related comorbidity such as hypertension, dyslipidemia, or obstructive sleep apnea, and does not have established ASCVD requiring a proven MACE agent today.

Tier 2 (Glycemia primary, established ASCVD): Semaglutide (Ozempic/Wegovy) or dulaglutide (Trulicity) should be prioritized given their published cardiovascular outcome trial data, until SURPASS-CVOT results become available.

Tier 3 (Cost-constrained, moderate glycemic target): Dulaglutide at 1.5 mg remains a reasonable, lower-cost option when A1C reduction of 1 to 1.4% is sufficient and weight loss is not the primary driver.

Current ADA Standards of Care (2024) recommend GLP-1 receptor agonists with proven cardiovascular benefit as preferred agents "in patients with type 2 diabetes and established ASCVD or high cardiovascular risk, regardless of baseline A1C." [11] Dulaglutide satisfies that criterion today; tirzepatide does not yet have final MACE trial data.

When Dulaglutide (Trulicity) Remains Appropriate

Three specific clinical scenarios favor dulaglutide in 2025:

1. The patient has type 2 diabetes with established cardiovascular disease or multiple risk factors and needs a proven MACE benefit now.
2. Insurance covers dulaglutide without prior authorization, but tirzepatide requires step therapy or is excluded from formulary.
3. The patient has a strong preference for a lower-complexity titration schedule (two doses: 0.75 mg and 1.5 mg) with a shorter on-market history of supply disruptions.

The 2020 ADA/EASD consensus statement on type 2 diabetes management lists dulaglutide as one of the agents with the highest level of cardiovascular evidence for MACE reduction. [12]

Switching Between Zepbound and Trulicity

Switching FROM Trulicity TO Zepbound

Clinicians switching a patient from dulaglutide to tirzepatide typically start tirzepatide at 2.5 mg once weekly, regardless of the dulaglutide dose the patient was receiving. There is no established equivalence ratio between dulaglutide and tirzepatide doses. The AACE/ACE Obesity Clinical Practice Guidelines recommend starting any new GLP-1 class agent at its lowest approved dose when transitioning from another agent in the same class, to manage GI tolerability during the switch period. [13]

The switch can be made without a washout period since both agents have similar half-lives (approximately 5 days for dulaglutide and approximately 5 days for tirzepatide). The patient can take the first tirzepatide dose on the day the next dulaglutide dose would have been due.

Expect A1C to remain stable or improve over the 12 weeks following the switch, and weight loss to accelerate meaningfully, particularly once tirzepatide is titrated to 10 or 15 mg.

Switching FROM Zepbound TO Trulicity

This direction is less common clinically and usually driven by cost, insurance coverage changes, or intolerance to tirzepatide's higher-dose GI effects. Patients switching down should be counseled that weight loss will likely plateau or partially reverse on dulaglutide, given its smaller pharmacological effect on appetite and fat oxidation.

Starting dulaglutide at 0.75 mg weekly for four weeks before advancing to 1.5 mg is the standard initiation approach outlined in Trulicity prescribing information. [3] No overlap or tapering of tirzepatide is required; the transition is a direct substitution timed to the next injection date.

Insurance, Formulary, and Cost Considerations

Insurance coverage is often the deciding factor in clinical practice. As of early 2025, Trulicity (dulaglutide) appears on more commercial formularies at Tier 2 or Tier 3 than Zepbound, largely because its lower list price and longer market presence have led to more negotiated contracts.

Zepbound's list price is approximately $1,059 per month for the 10 mg dose without manufacturer savings. Eli Lilly offers a savings card that can reduce out-of-pocket cost to $550 per month for commercially insured patients who are eligible. Dulaglutide's list price runs approximately $800 per month, with generic biosimilar versions expected after patent expiration.

Medicare Part D covers Zepbound for obesity only under specific Part D plans following the Inflation Reduction Act provisions; coverage remains variable by plan. Medicare does not currently cover anti-obesity medications broadly, though policy discussions are ongoing. [14]

Safety Considerations Specific to Each Agent

Both drugs share the GLP-1 class warning for thyroid C-cell tumors observed in rodent studies, though human relevance has not been established. Both are contraindicated in patients with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2. [2,3]

Acute pancreatitis is a labeled risk for both agents. Patients with a history of pancreatitis should use either drug with caution, and therapy should be discontinued if pancreatitis is confirmed. Rates of pancreatitis in SURMOUNT-1 with tirzepatide were low (0.2%) and comparable to placebo. REWIND reported a similarly low frequency with dulaglutide.

Diabetic retinopathy worsening has been observed with rapid glycemic improvement on GLP-1 agents and tirzepatide, a class-level phenomenon also seen with insulin intensification. Baseline eye examination and monitoring during the first 6 months of therapy are prudent in patients with pre-existing retinopathy. [11]

What Real Patients Experience: Adherence and Persistence Patterns

Adherence data from pharmacy fill records provide a grounded view that trial completion rates do not capture. A 2024 analysis using OptumRx data (N=24,511 tirzepatide initiators, N=19,042 dulaglutide initiators) found 12-month medication possession ratios (MPR) of 0.67 for tirzepatide and 0.71 for dulaglutide. [9] Both figures reflect meaningful non-adherence.

The most common reasons for tirzepatide discontinuation in that dataset were GI intolerability (cited by 22% of discontinuers) and insurance coverage loss (31%). For dulaglutide, inadequate efficacy (meaning insufficient A1C reduction or weight loss to meet patient or clinician targets) drove 38% of discontinuations.

That difference is telling. Patients stop tirzepatide because of side effects or cost. Patients stop dulaglutide because it does not work well enough for their goals.