STEP-5 Cost, Cost-Effectiveness, and Health-Economic Implications

At a glance

Why Economic Analysis of STEP-5 Is Distinct From Other STEP Trials

Most cost-effectiveness analyses of semaglutide 2.4 mg have used data from STEP-1, the largest of the four key trials. STEP-5 is smaller, enrolling 304 adults, but it provides something STEP-1 cannot: a full two-year placebo-controlled weight trajectory. That matters for economic modeling because obesity pharmacotherapy is not a one-time intervention. Cost-per-QALY estimates depend critically on whether weight loss is maintained over time or attenuates after the first year.

The STEP-5 primary publication in Nature Medicine showed that at week 104, participants randomized to semaglutide had lost 15.2% of body weight versus 2.6% for placebo. The weight loss trajectory remained stable from roughly week 60 onward, with no meaningful regain through week 104 in the active treatment arm. That plateau, rather than a decline, is the single most important input for any economic model that projects health outcomes beyond the trial window.

When analysts feed an attenuating weight-loss curve into a Markov or discrete-event simulation, costs per QALY rise substantially because downstream benefits (reduced incidence of type 2 diabetes, cardiovascular events, and sleep apnea-related morbidity) are proportional to maintained weight reduction. STEP-5's durable trajectory therefore produces more favorable cost-effectiveness ratios than models forced to assume gradual regain after 12 months.

How Economic Models Are Built From STEP-5 Data

The Modeling Framework

Health-technology assessment bodies including ICER (Institute for Clinical and Economic Review) use microsimulation or Markov state-transition models to translate weight change into lifetime QALYs. The standard approach maps percentage weight loss to risk reductions for incident type 2 diabetes (via the Diabetes Prevention Program equation), major adverse cardiovascular events, hypertension, dyslipidemia, and obesity-related cancers. Each avoided event contributes to both QALY gains and cost offsets.

The STEP-5 dataset inputs to these models include:

• Baseline BMI (mean 38.5 kg/m² in the trial)
• Absolute weight loss at 104 weeks (mean 15.2% or approximately 15.6 kg from a mean baseline of approximately 103 kg)
• Proportion of participants achieving ≥5%, ≥10%, and ≥15% weight loss thresholds
• Discontinuation rate (approximately 13.5% in the semaglutide arm over 104 weeks)
• Adverse-event rates that affect quality-of-life utilities (predominantly gastrointestinal)

ICER's Cost-Per-QALY Range

In its 2022 evidence report on GLP-1 and GIP/GLP-1 agonists for obesity, ICER modeled semaglutide 2.4 mg using a blended dataset including STEP-1 and STEP-5 trajectory data. At the US wholesale acquisition cost (WAC) of approximately $1,349 per month (roughly $16,200 per year), the estimated incremental cost-effectiveness ratio ranged from $130,000 to $180,000 per QALY gained in adults with BMI ≥30. For the subgroup with BMI ≥30 plus established cardiovascular disease or type 2 diabetes, the estimate improved to approximately $110,000 to $150,000 per QALY because avoided downstream costs are higher in that population.

These figures exceed the conventional US threshold of $100,000 to $150,000 per QALY, which means semaglutide at list price sits at the boundary of cost-effectiveness acceptability by standard benchmarks. The ICER report estimated that a price reduction to approximately $7,500 to $9,800 per year (net of rebates) would bring the drug within a $150,000/QALY threshold for adults with at least one comorbidity.

| Scenario | Annual Drug Cost Assumed | ICER Estimate (per QALY) | Within $150K Threshold? | |---|---|---|---| | WAC, BMI ≥30, no comorbidities | ~$16,200 | ~$175,000 | No | | WAC, BMI ≥30, ≥1 comorbidity | ~$16,200 | ~$130,000 | Borderline | | Net price ~$9,000, BMI ≥30, ≥1 comorbidity | ~$9,000 | ~$85,000 | Yes | | Net price ~$7,500, all BMI ≥30 | ~$7,500 | ~$95,000 | Yes |

Sources: ICER 2022 obesity evidence report; STEP-5 primary trial.

List Price vs Net Price: The Gap That Changes Everything

Published cost-effectiveness analyses almost always model WAC because net prices (after rebates paid to pharmacy benefit managers and insurers) are confidential. The gap between WAC and net price for branded GLP-1 agonists has historically been 40% to 60% in commercial markets, though the precise figures for Wegovy (semaglutide 2.4 mg) remain undisclosed.

Novo Nordisk's FDA-approved label for Wegovy positions the drug for adults with initial BMI ≥30 kg/m² or ≥27 kg/m² with at least one weight-related comorbidity. If commercial rebates for this indication approach those seen for semaglutide 1.0 mg (Ozempic, approved for type 2 diabetes), net annual costs could fall to $8,000 to $10 to 000 in broad commercial formularies, substantially shifting cost-effectiveness calculations.

For the Medicare population specifically, the Inflation Reduction Act created new negotiation authority for selected drugs, though weight-loss-only indications have faced separate coverage restrictions under traditional Medicare Part D. The SELECT trial, which demonstrated a 20% reduction in major adverse cardiovascular events with semaglutide 2.4 mg in adults with obesity and established cardiovascular disease, has added pressure on CMS to broaden coverage, since a cardiovascular indication changes the payer calculus entirely.

Cost Per Kilogram Lost: A Patient-Facing Metric

Cost per QALY is a population-level construct that individual patients rarely find intuitive. A more accessible metric is cost per kilogram of body weight lost over the treatment period.

Using STEP-5 data directly: the mean weight loss in the semaglutide arm was approximately 15.6 kg over 104 weeks. At WAC of $16,200 per year, the two-year drug cost is $32,400. Cost per kilogram lost (drug cost only, ignoring injection supplies and monitoring visits) is therefore approximately $2,077 per kg.

For comparison, bariatric surgery (Roux-en-Y gastric bypass) produces approximately 25 to 35 kg of sustained weight loss at a one-time procedural cost of roughly $20,000 to $35 to 000 in US centers, yielding a cost-per-kilogram-lost in the range of $600 to $1,200. However, surgery carries procedural risk, requires lifelong nutritional monitoring, and is not appropriate for all patients. The pharmacotherapy alternative requires indefinite continuation to maintain weight loss, as demonstrated by the STEP-1 withdrawal extension, where participants who discontinued semaglutide regained approximately two-thirds of lost weight within one year.

This regain risk, documented in post-STEP-1 extension data published in Diabetes, Obesity and Metabolism, means that the effective cost of pharmacotherapy is ongoing rather than bounded. Over a 10-year horizon at net price ($9,000/year), total drug expenditure reaches $90,000 before accounting for rebates, co-pay assistance, or any potential generic entry.

Payer Coverage Realities and Formulary Design

As of mid-2024, coverage of semaglutide 2.4 mg for obesity without a specific cardiovascular or diabetic indication remains highly variable across US commercial payers. Several large employers and state Medicaid programs have restricted or excluded coverage due to budget impact concerns. A Health Affairs analysis published in 2023 estimated that universal coverage of GLP-1 agonists at list price for all eligible US adults could add $145 billion to $265 billion annually to national drug expenditures, a figure that explains formulary resistance independent of per-patient cost-effectiveness.

The practical result for patients is a tiered system where access correlates heavily with insurance type and employer benefit design. Patients with employer-sponsored plans that include obesity pharmacotherapy coverage, patients who qualify for Novo Nordisk's patient assistance program, and those enrolled in clinical programs with outcomes-based contracts face meaningfully different effective costs than patients paying out of pocket.

Criticisms of Existing Economic Models

Several methodological limitations affect all published economic analyses that draw on STEP-5:

Extrapolation uncertainty. STEP-5 provides 104 weeks of data. Most cost-effectiveness models project outcomes over 10, 20, or lifetime horizons. Weight-loss maintenance beyond two years without a placebo-controlled comparator is assumed rather than directly observed, though real-world registry data from LEADER and other long-term GLP-1 studies provide partial support for durability assumptions.

Utility weights. The quality-of-life gains assigned to weight reduction vary substantially across models. If the model uses utilities derived from obese populations with significant comorbidities, QALY gains are higher. STEP-5's population had a mean BMI of 38.5 with relatively lower rates of established diabetes than STEP-2, which could mean baseline utility was higher and incremental QALY gain from weight loss is smaller than in more metabolically compromised cohorts.

Adverse-event costs. Gastrointestinal adverse events (nausea in approximately 44% of semaglutide participants in STEP-5) are frequently underweighted in published models, affecting both cost and disutility estimates.

Discontinuation modeling. Real-world discontinuation rates exceed trial rates substantially. A 2024 analysis of commercial claims data found 12-month persistence rates of approximately 30% for GLP-1 agonists prescribed for obesity. Models using trial-based discontinuation rates will overestimate long-term effectiveness and underestimate effective cost per outcome.

Frequently asked questions

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References

1. Garvey WT, Batterham RL, Bhatta M, et al. Two-year effects of semaglutide in adults with overweight or obesity: the STEP 5 trial. Nature Medicine. 2022;28(10):2083-2091. https://pubmed.ncbi.nlm.nih.gov/36280822/

2. Institute for Clinical and Economic Review. Overweight and Obesity: Effectiveness and Value of Pharmacologic Treatments. ICER Evidence Report. 2022. https://icer.org/assessment/obesity-2022/

3. Novo Nordisk. Wegovy (semaglutide) injection 2.4 mg prescribing information. US FDA. 2021. https://www.accessdata.fda.gov/drugsatfda_docs/label/2021/215256s000lbl.pdf

4. Wilding JPH, Batterham RL, Davies M, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes, Obesity and Metabolism. 2022;24(8):1553-1564. https://pubmed.ncbi.nlm.nih.gov/35441470/

5. Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes. New England Journal of Medicine. 2023;389(24):2221-2232. https://pubmed.ncbi.nlm.nih.gov/37952131/

6. Dieleman JL, Cao J, Chapin A, et al. US health care spending by payer and health condition, 1996-2016. JAMA. 2020;323(9):863-884. https://pubmed.ncbi.nlm.nih.gov/32125369/