SURMOUNT-2 Cost, Cost-Effectiveness, and Health-Economic Implications

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SURMOUNT-2 Cost, Cost-Effectiveness, and Health-Economic Implications

At a glance

| Trial variable | Detail | |---|---| | Trial name | SURMOUNT-2 | | N | 938 | | Intervention | Tirzepatide 5 mg, 10 mg, or 15 mg once weekly | | Comparator | Placebo once weekly | | Population | Adults with BMI ≥27, type 2 diabetes (HbA1c 7 to 10%), on stable background therapy | | Duration | 72 weeks | | Primary endpoint | Percent change in body weight from baseline at 72 weeks | | Key result | −15.7% (15 mg), −13.4% (10 mg), −8.6% (5 mg) vs −3.3% placebo | | Journal / Year | Lancet, 2023 | | Primary source | PubMed 37331373 |

Why the Economics of SURMOUNT-2 Are Not Straightforward

Most cost-effectiveness analyses in diabetes focus on glycemic outcomes: HbA1c reduction, microvascular event rates, avoided dialysis. SURMOUNT-2 is unusual because it sits at the intersection of two separate disease categories. Its population carries both obesity (BMI ≥27 with at least one weight-related comorbidity) and type 2 diabetes, which means payers must simultaneously justify coverage under a metabolic benefit framework and an obesity drug framework, two categories with historically very different reimbursement cultures.

The SURMOUNT-2 trial randomized 938 participants and reported not just weight outcomes but also clinically meaningful reductions in HbA1c (mean −2.1 percentage points at 15 mg) and cardiometabolic biomarkers. Any honest economic model must decide whether to count those glycemic benefits separately from the weight benefits, and most models published to date do not handle that dual-benefit accounting consistently, which is one reason published ICER estimates vary so widely.

The List-Price Starting Point

Eli Lilly launched tirzepatide as Mounjaro (for T2D) in 2022 and as Zepbound (for obesity) in late 2023. The FDA label for Mounjaro covers the T2D indication relevant to SURMOUNT-2's population. At the time of the SURMOUNT-2 publication, the Mounjaro list price was approximately $1,023 per four-week supply, or roughly $13,300 annually before any discounts. Zepbound launched at a slightly lower list price of approximately $1,060 per month for the obesity label.

The critical methodological point is that list price and net price are not the same number, and the gap is large. Manufacturer rebates to pharmacy benefit managers typically reduce effective payer cost by 20 to 40 percent for branded injectable medications in this class. A model running on list price will generate a cost-per-QALY that looks unfavorable; the same model at a 35 percent net price discount can shift the ICER by $40,000 to $60,000 per QALY in the favorable direction. Published academic models rarely have access to actual contract terms, so they typically present sensitivity analyses across a price range rather than a single number.

What Cost-Effectiveness Models Actually Measure

A QALY (quality-adjusted life year) weights survival by health-related quality of life on a 0-to-1 scale. An ICER (incremental cost-effectiveness ratio) divides the extra cost of a treatment by the extra QALYs it generates. The conventional U.S. threshold used by the Institute for Clinical and Economic Review (ICER) is $100,000 to $150,000 per QALY, though that threshold is debated and not binding on any payer.

For weight-loss drugs, the QALY gain calculation depends on two inputs that are themselves uncertain. First, how much does a given degree of weight loss improve health-related quality of life? The utility weights used in obesity models vary substantially across instruments (EQ-5D vs SF-6D, for example), and the SURMOUNT-2 trial used patient-reported outcome measures including the IWQOL-Lite-CT, which does not map directly into QALY calculations without additional conversion assumptions. Second, how much does sustained weight loss reduce downstream events, cardiovascular disease, progression to more severe diabetes complications, sleep apnea hospitalizations? Most models extrapolate from epidemiological associations rather than from direct event data in tirzepatide trials, since SURMOUNT-2 was not powered or designed as a cardiovascular outcomes trial.

That second limitation is changing. The SURPASS-CVOT trial (tirzepatide vs dulaglutide) and the separate SELECT-equivalent cardiovascular outcomes study in obesity will eventually supply hard event data. Until then, modelers are estimating.

Published ICER Estimates: What the Models Actually Found

ICER released a formal assessment of GLP-1 and dual GIP/GLP-1 agonists for obesity in 2023. Their base-case analysis placed tirzepatide at approximately $132,000 per QALY at list price for a population that approximates the SURMOUNT-2 cohort (obese adults with type 2 diabetes or cardiometabolic risk factors). At a 25 percent net price discount, the estimate moved to approximately $99,000, placing it just below the upper bound of the conventional threshold. A 40 percent discount brought the estimate to roughly $79,000.

| Price assumption | Estimated ICER (tirzepatide vs placebo+lifestyle) | |---|---| | List price (~$13,300/yr) | ~$132,000 per QALY | | 25% net discount (~$9,975/yr) | ~$99,000 per QALY | | 40% net discount (~$7,980/yr) | ~$79,000 per QALY | | 50% net discount (~$6,650/yr) | ~$66,000 per QALY |

Approximate ranges drawn from publicly available ICER 2023 evidence report modeling; individual model assumptions vary.

These figures are sensitive to the assumed durability of weight loss. SURMOUNT-2 was 72 weeks. If weight loss is maintained for 5 to 10 years (as the model must assume to generate lifetime cost-effectiveness), the QALY gains accumulate and the ICER improves. If patients discontinue the drug, or if the withdrawal data from the SURMOUNT-4 trial (which showed substantial weight regain after stopping tirzepatide) is factored in, the ICER worsens because the model must either assume indefinite therapy cost or reduced long-term benefit. The SURMOUNT-4 findings are directly relevant here: patients who switched from tirzepatide to placebo regained a mean of 14 percentage points of body weight over 88 weeks, which effectively forces a binary modeling assumption of either lifetime drug use or limited long-term efficacy.

Payer Coverage Logic and the T2D Carve-Out

One underappreciated aspect of the SURMOUNT-2 data is how it sits within payer coverage architecture. Commercial payers have historically covered GLP-1 agonists for type 2 diabetes with relatively low barriers. The Mounjaro label covers T2D glycemic management, and most commercial formularies included it on tier 2 or tier 3 with prior authorization by 2023. The obesity label (Zepbound) faced a separate and much harder coverage environment. The majority of commercial plans and Medicare Part D (under the pre-IRA framework) explicitly excluded obesity-only indications.

For a patient who appears to SURMOUNT-2: someone with a BMI of 30 and a hemoglobin A1c of 8.2 percent, the prescribing code matters enormously. Prescribed as an antidiabetic with weight benefit, coverage is often available. Prescribed as an obesity treatment, it is often denied. This creates a practical situation in which the clinical outcomes from SURMOUNT-2 are accessible to T2D patients but formally unavailable to identical patients whose diabetes has been controlled and whose primary remaining problem is obesity.

The Inflation Reduction Act Medicare drug negotiation provisions and the proposed TREAT and HOPE for Obesity Acts in the U.S. Congress represent the main policy pathways toward changing the Medicare obesity exclusion. If Medicare were to cover obesity-indicated GLP-1/GIP agonists, the budget impact would be substantial: ICER estimated a potential $14 billion annual increase in federal drug spending for this drug class in an obesity-coverage scenario, which is a key reason coverage expansion has moved slowly despite the SURMOUNT-2 and SURMOUNT-1 data.

The Individual Patient Value Calculation

From a clinical translation standpoint, the economic question for an individual patient is different from the societal cost-per-QALY question. For a patient with T2D and obesity who is considering starting tirzepatide, the relevant calculation involves their out-of-pocket cost after insurance, the probability that they will be a good responder, and the magnitude of benefit they can expect.

The SURMOUNT-2 trial reported that 82.8 percent of participants on 15 mg achieved at least 5 percent weight loss (versus 32.1 percent on placebo), and 55.5 percent achieved at least 15 percent weight loss (versus 4.0 percent on placebo). These response rates matter for individual value because a patient who achieves 15 percent or more weight loss captures a meaningfully larger share of the QALY benefit than the average trial participant. Predictors of non-response (early <5% weight loss by week 12) could, in principle, be used to guide early discontinuation decisions before significant cost accrues, though no tirzepatide-specific stopping-rule guidance has been published as of 2024.

For patients with commercial insurance and a Lilly Mounjaro Savings Card, out-of-pocket costs dropped to as low as $25 to $35 per month during early commercial availability, dramatically shifting the individual value equation. For uninsured patients paying list price, the annual cost of approximately $13,000 is likely not cost-effective relative to individualized alternatives unless the patient has a very high baseline cardiometabolic risk and significant co-morbid disease burden.

Methodological Limitations in Existing Economic Models

Several limitations in current SURMOUNT-2-derived economic analyses deserve explicit attention. First, most models use a single mean weight loss trajectory, when the trial showed substantial variance. Using the mean −15.7% at 15 mg obscures the fact that a meaningful fraction of patients lost 20 percent or more and another fraction lost less than 5 percent. A distribution-sensitive model would generate a wider and arguably more honest ICER range.

Second, the T2D population in SURMOUNT-2 was on stable background therapy (metformin, sulfonylureas, SGLT-2 inhibitors). The potential for tirzepatide to replace or reduce those background agents, with their associated costs and side effects, is rarely modeled as an offset to drug cost, even though intensification and de-intensification of T2D regimens represent real downstream costs.

Third, the utility mapping from IWQOL-Lite-CT to EQ-5D or preference-based QALYs involves cross-instrument conversion algorithms that introduce non-trivial uncertainty. The ADA Standards of Care in Diabetes 2024 now include tirzepatide in their weight management section, which provides clinical legitimacy but does not resolve the quality-of-life measurement problem.

What Clinicians and Patients Should Take Away

The cost story for tirzepatide in T2D is conditional rather than settled. At net prices with commercial coverage and savings programs, the drug is likely cost-effective for patients with meaningful obesity and suboptimally controlled T2D. At list price without coverage, the economic case is harder unless the patient carries very high downstream risk. The dual-indication positioning means that for the typical SURMOUNT-2-type patient, the T2D coding pathway remains the more reliable route to coverage access while obesity-specific reimbursement policy evolves.

Frequently asked questions

›What was the primary endpoint and main result in SURMOUNT-2?
›How does tirzepatide's cost-effectiveness compare to semaglutide in T2D?
›Does Medicare cover tirzepatide for patients like those in SURMOUNT-2?
›What net price discount makes tirzepatide cost-effective under conventional thresholds?
›What happens to cost-effectiveness if a patient stops tirzepatide?
›Are there predictors of who will be a strong responder in the SURMOUNT-2 population?
›How should clinicians frame the value discussion with T2D patients considering tirzepatide?
›Does SURMOUNT-2 include cardiovascular outcome data that could strengthen the economic case?
›How does the dual Mounjaro/Zepbound labeling affect payer coverage decisions?
›What are the biggest gaps in the current economic evidence base for SURMOUNT-2?

References

  1. 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. PubMed 37331373

  2. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216. PubMed 36966843

  3. U.S. Food and Drug Administration. Mounjaro (tirzepatide) Prescribing Information. Eli Lilly and Company. FDA label

  4. Institute for Clinical and Economic Review. GLP-1 Agonists and Dual GIP/GLP-1 Agonists for Adults with Obesity: Effectiveness and Value. ICER Evidence Report. 2023. icer.org

  5. American Diabetes Association. Standards of Care in Diabetes 2024. Diabetes Care. 2024;47(Supplement 1):S1-S321. diabetesjournals.org

  6. Aronne LJ, Sattar N, Horn DB, et al. Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity (SURMOUNT-4). JAMA. 2024;331(1):38-48. PubMed 38078870