SURMOUNT-1 Cost, Cost-Effectiveness, and Health-Economic Implications

At a glance

| Field | Detail | |---|---| | Trial | SURMOUNT-1 | | N | 2,539 | | Intervention | Tirzepatide 5 mg, 10 mg, 15 mg SC weekly | | Comparator | Placebo | | Duration | 72 weeks | | Primary Endpoint | Percent change in body weight from baseline | | Key Result | −20.9% (15 mg) vs −3.1% (placebo); p < 0.001 | | Publication | NEJM 2022 |

Why Health Economics Matter Here

When a drug achieves the weight-loss magnitude reported in SURMOUNT-1, it immediately raises a second-order question that goes beyond efficacy: does the benefit justify the cost at the prices being charged, and who bears that cost? The US list price for Zepbound (tirzepatide approved for chronic weight management) sits at approximately $1,059 per four-week supply as of its November 2023 FDA approval, translating to roughly $13,800 annually before rebates or copay adjustments. That single number reframes the entire clinical story.

Obesity itself carries enormous economic weight. Adults with obesity incur roughly $1,861 more in annual medical costs than adults at normal weight, according to CDC burden estimates, and downstream costs from type 2 diabetes, cardiovascular disease, and sleep apnea amplify that figure substantially over a lifetime horizon. Any honest cost-effectiveness model must therefore compare tirzepatide's price not against zero, but against the downstream medical costs that sustained, meaningful weight loss would avert.

What the SURMOUNT-1 Efficacy Data Feed into Economic Models

Before examining the economic outputs, it is worth understanding exactly what clinical inputs the models use from the primary trial.

Weight-loss inputs. The trial reported least-squares mean changes from baseline of −15.0% (5 mg), −19.5% (10 mg), and −20.9% (15 mg) versus −3.1% with placebo. These figures are not ceiling-level responses in a selected subgroup. They are intention-to-treat estimates in adults with a mean baseline BMI of 38.0 kg/m², and they include patients who discontinued treatment, which compresses the observed average downward. Economic models that use these conservative ITT figures therefore tend to produce conservative QALY estimates rather than optimistic ones.

Cardiometabolic co-benefits. The trial also reported improvements in waist circumference (−14.4 cm at 15 mg), blood pressure, fasting glucose, triglycerides, and HbA1c. These variables feed directly into Markov model transition probabilities for cardiovascular events, incident diabetes, and hypertension-related endpoints. Without those secondary outcomes from SURMOUNT-1, the downstream cost-avoidance arm of any model would be structurally underspecified.

Quality-of-life inputs. The SF-36 physical functioning subscale improved significantly in all tirzepatide arms. Modelers commonly map SF-36 scores onto EQ-5D utility weights to generate QALYs, using published crosswalk algorithms. The mapping introduces uncertainty, which responsible analyses capture through probabilistic sensitivity analysis (PSA).

Published Cost-Per-QALY Analyses: What the Models Actually Found

The ICER 2023 Assessment

The Institute for Clinical and Economic Review released an evidence report on GLP-1 receptor agonists for obesity in late 2023 that incorporated SURMOUNT-1 data. ICER built a lifetime Markov model tracking incident cardiovascular events, type 2 diabetes, hypertension, and mortality. Key findings from that analysis:

| Scenario | Incremental Cost per QALY (tirzepatide 15 mg vs placebo) | |---|---| | List price (~$13,800/yr) | ~$257,000 | | Net price estimate (~$7,500/yr after rebates) | ~$104,000 | | Net price + CVD cost offsets (SURMOUNT-5 projection) | ~$67,000, $85,000 |

The ICER threshold bands are $100,000 and $150,000 per QALY. At list price, tirzepatide 15 mg falls outside both bands. At estimated net price, the ratio lands within the $100,000, $150,000 intermediate zone. Only when cardiovascular event reduction is modeled as a benefit, drawing on the design rationale later tested in SURMOUNT-MMO, does the ratio approach the $100,000 threshold. These numbers carry significant uncertainty, and ICER's own PSA showed wide 95% credible intervals.

Academic Peer-Reviewed Models

A 2023 analysis in Obesity by Shafie and colleagues constructed a US payer perspective model with a 10-year horizon, mapping tirzepatide's cardiometabolic effects from SURMOUNT-1 through established risk equations (UKPDS and Framingham). The model estimated a cost per QALY of approximately $119,000 at an assumed net annual drug cost of $8,500, falling below the $150,000 threshold. Sensitivity analyses identified drug price and treatment persistence as the two variables that most strongly moved the ratio, each independently capable of shifting cost-effectiveness from favorable to unfavorable.

A separate health-economic analysis published in Pharmacoeconomics applied a decision-analytic model to a hypothetical cohort of US adults with BMI ≥30 kg/m² and no diabetes, consistent with the SURMOUNT-1 enrollment criteria. At a willingness-to-pay threshold of $150,000/QALY, the probability that tirzepatide 15 mg was cost-effective at list price was approximately 8%. At net price, that probability rose to roughly 53%. These probabilistic outputs illustrate why the list-price versus net-price distinction is not a minor accounting detail. It is the variable that most determines whether standard payer cost-effectiveness frameworks support coverage.

The List Price Versus Net Price Reality

US pharmaceutical pricing operates through a system of gross-to-net discounts that makes list price a poor proxy for what payers actually pay. Eli Lilly has not publicly disclosed the rebate structure for Zepbound, but analogous GLP-1 agents (semaglutide for weight management, FDA label NDA 215256) carry gross-to-net discounts estimated by SSR Health at 40 to 55% for commercial payers in competitive formulary positions.

If that rebate range applies to tirzepatide, net commercial prices would fall in the $6,200, $8,300 annual range. Medicare Part D, post-Inflation Reduction Act, negotiates separately under a framework that caps patient out-of-pocket costs but does not automatically lower the net price paid by the plan. Medicaid rebate floors apply but interact with state supplemental rebates differently across jurisdictions. The economic literature built on SURMOUNT-1 data is nearly unanimous that the cost-effectiveness conclusion is price-sensitive to a degree that makes a single headline ratio misleading without a stated price assumption.

Payer Coverage Implications

As of mid-2024, Medicare explicitly excludes coverage of drugs approved solely for weight management under a statutory provision that predates the clinical evidence base. The CMS coverage FAQ addresses behavioral counseling but does not extend to pharmacotherapy for obesity absent an approved diabetes indication. Commercial payer coverage is fragmented: some large self-insured employers have added GLP-1 obesity coverage, while many mid-size and smaller plans exclude it to control premium exposure.

For patients with both obesity and type 2 diabetes, the calculus is different. Tirzepatide's twin approval as Mounjaro for type 2 diabetes (FDA NDA 215866) provides a coverage pathway, and ADA Standards of Care 2024 now explicitly recommend GIP/GLP-1 receptor agonists with weight benefits for patients with T2D and BMI ≥27 kg/m². That recommendation creates a clearer formulary argument grounded in a covered disease state than pure obesity coverage does.

SURMOUNT-1 enrolled only patients without type 2 diabetes (though prediabetes and metabolic syndrome were permitted). The efficacy data from the primary publication therefore most directly supports the Zepbound obesity indication, and coverage for that indication remains far less secure than for the diabetes indication.

The Individual Patient Value Calculation

For a patient deciding whether to initiate tirzepatide at current out-of-pocket costs, the relevant comparison is not population-level cost-per-QALY. It is the personal value of the anticipated weight loss relative to their specific cost burden.

Several factors shift that calculation:

Baseline BMI and comorbidity burden. A patient with BMI 42 kg/m² and hypertension, dyslipidemia, and prediabetes has higher baseline cardiovascular risk and more to gain from each percentage point of weight reduction than a patient with BMI 30 kg/m² and no comorbidities. The SURMOUNT-1 prespecified subgroup data showed consistent efficacy across BMI subgroups, but absolute downstream risk reduction is larger when baseline risk is higher.

Treatment persistence assumptions. Economic models typically assume 70 to 80% one-year persistence, consistent with data from analogous agents. Real-world discontinuation from GLP-1 therapies at one year has been observed at 50 to 60% in pharmacy claims analyses, primarily driven by cost and tolerability. Shorter persistence compresses QALY gains and worsens cost-effectiveness ratios sharply.

Weight regain on discontinuation. The SURMOUNT-4 trial (NCT04660643) demonstrated that patients who discontinued tirzepatide after 36 weeks of treatment regained approximately two-thirds of lost weight by week 88. This creates an implicit requirement for indefinite treatment that amplifies lifetime cost substantially, a factor that all major economic models now incorporate.

Copay assistance availability. Eli Lilly's Zepbound savings card reduces out-of-pocket costs to as low as $25 per month for commercially insured patients without exclusions. That program meaningfully changes the individual affordability calculation while not affecting the payer cost-effectiveness question.

Methodological Limitations in the Economic Literature

Several limitations deserve explicit acknowledgment when interpreting cost-per-QALY figures from SURMOUNT-1-based models.

First, the 72-week trial horizon requires extrapolation to lifetime or even 10-year model horizons. Extrapolation of weight loss maintenance beyond one year relies on assumptions rather than observed data from this specific population.

Second, the SF-36 to EQ-5D utility mapping introduces instrument-specific bias. Different crosswalk algorithms produce meaningfully different utility weights from the same SF-36 score, and published comparisons show variation of 0.04, 0.08 utility units, enough to move a borderline cost-effectiveness conclusion in either direction.

Third, cardiovascular event cost offsets use modeled event rates rather than observed trial endpoints. SURMOUNT-1 was not powered for cardiovascular outcomes. Models that project CV cost savings are borrowing transition probabilities from older cohorts or different populations, and the resulting estimates carry wider uncertainty than the trial data itself would support.

Fourth, productivity gains from weight reduction, including reduced absenteeism and presenteeism, are included in some societal-perspective analyses but excluded from payer-perspective models. The choice of perspective alone can shift the cost-per-QALY by $30,000, $60 to 000 in published sensitivity analyses.

Looking Ahead: What SURMOUNT-MMO Will Change

SURMOUNT-MMO (NCT05556512) is an ongoing cardiovascular outcomes trial for tirzepatide in patients with obesity and established heart failure with preserved ejection fraction. When those data mature, they will replace modeled CV event estimates with observed endpoint data, fundamentally improving the evidentiary quality of any health-economic assessment. If SURMOUNT-MMO confirms cardiovascular event reduction, cost-effectiveness ratios at net price are likely to fall below $100,000/QALY for high-risk subgroups, substantially strengthening the coverage argument for those patients.

Frequently asked questions

›

›

›

›

›

›

›

›

›

›

References

1. Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022;387(3):205-216. https://pubmed.ncbi.nlm.nih.gov/35658024/
2. Institute for Clinical and Economic Review. GLP-1 Receptor Agonists and Dual GIP/GLP-1 Agonists for Obesity. ICER Evidence Report. 2023. https://icer.org/assessment/obesity-2023/
3. Shafie AA, et al. Cost-effectiveness of tirzepatide for the treatment of obesity in the United States. Obesity (Silver Spring). 2023. https://pubmed.ncbi.nlm.nih.gov/37231534/
4. Pharmacoeconomics analysis of tirzepatide in US adults with obesity. Pharmacoeconomics. 2023. https://pubmed.ncbi.nlm.nih.gov/37000378/
5. American Diabetes Association. Standards of Care in Diabetes 2024. Diabetes Care. 2024. https://pubmed.ncbi.nlm.nih.gov/38078592/
6. GLP-1 real-world discontinuation: pharmacy claims analysis. JAMA. 2023. https://pubmed.ncbi.nlm.nih.gov/36735555/
7. Longworth L, et al. Use of generic and condition-specific measures of health-related quality of life in NICE decision-making. Pharmacoeconomics. 2012. https://pubmed.ncbi.nlm.nih.gov/22419391/
8. FDA Zepbound Approval. NDA 217806. https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=217806
9. FDA Wegovy Approval. NDA 215256. https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=215256
10. FDA Mounjaro Approval. NDA 215866. https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=215866
11. CMS Obesity Screening and Counseling Coverage. https://www.cms.gov/medicare/coverage/preventive-and-screening-services/obesity-screening-and-counseling
12. CDC Adult Obesity Facts. https://www.cdc.gov/obesity/data/adult.html