Background

As the use of glucagon-like peptide-1 (GLP-1) agonist therapies continues to expand, so does the body of research evaluating their impact on health outcomes and medical costs. With other studies now available, it’s not uncommon to see differing conclusions — particularly when comparing the differences between Prime Therapeutics’ (Prime) Year-2 findings, and those recently published by Aon. As a result, we would like to explain these findings, how they differ from Prime’s study and what it means.

A look into Aon’s analysis

Aon, a benefits consulting firm, recently released a study analyzing changes in medical spending and health care resource utilization (HCRU) over two years. The study included 139,000 individuals — most of whom were living with diabetes — who initiated GLP-1 therapies (Wegovy, Mounjaro, or Ozempic) in 2022, compared to matched controls. Only individuals who were adherent to the GLP-1 therapy for two years were assessed. 

Key findings from Aon: 

• Medical spending: 7% reduction in Year-2 vs. Year-1 
  • GLP-1 users: $1,050 → $1,120 
  • Controls: $970 → $1,110 
• Cardiovascular outcomes: 44% lower risk of hospitalizations due to major adverse cardiovascular events (MACE), however absolute reduction in MACE events was 0.25%, therefore need to treat ~400 people to prevent one MACE event 
• Chronic conditions: Reduced HCRU across a range of conditions, however, there were also a range of conditions that had increases

Prime’s year-2 findings

Prime’s study was a real-world design focused specifically on individuals without diabetes who initiated GLP-1 therapy for obesity and assessed all members, regardless of their GLP-1 therapy adherence. 

Key findings from Prime, Year 2 compared to baseline change: 

• Total cost of care: $4,206 higher in Year-2 vs. matched controls 
• Medical spending: $670 increase among GLP-1 group compared to matched controls 
  • GLP-1 initiators Year-2 compared to their baseline difference: $1,460 higher 
  • Matched control Year 2 compared to their baseline difference: $790 higher 
  • GLP-1 group change compared to matched control change (i.e., difference-in-difference): $670 

Note: these findings suggest a potential association between GLP-1 therapy and increased cost in this population, though further research is needed to understand causality.

Explaining the discrepancies

Prime’s Health Outcomes team has examined the Aon analysis and identified several notable differences with Prime’s ongoing research, which explains why the findings may differ. The chart below provides an at-a-glance view into the key differences between the two studies:

Key differences in detail: 

• Population focus: Aon’s cohort includes mostly individuals with diabetes, while Prime’s isolates those without diabetes using GLP-1s for obesity — two distinct populations with different health trajectories. 
• Adherence bias: Aon excluded nonadherent users, which likely influence outcomes by focusing on a more engaged treatment population. Prime included both adherent and nonadherent users to reflect real-world usage. 
• Baseline comparison: Aon compared Year-2 to Year-1, omitting baseline context. Prime’s comparison to Year-0 offers a more comprehensive view of cost trends. 
• Cardiovascular events: Aon reported a 0.25 percentage point reduction in MACE, implying 400 individuals would need to be treated for two years to prevent one event. Prime observed a slightly lower MACE rate among adherent users, but no significant difference in Year-2 or among the full cohort. Differences in MACE outcomes may reflect variations in population health status, adherence, and study design.

Aon’s focus on all GLP-1 utilizers both for diabetes and weight loss without diabetes, as well as, limiting to those adherent to GLP-1 therapy for two years, limits comparability with Prime’s analysis. That said, the conversation around GLP-1 therapies is far from over. 

Prime’s GLP-1 Year-3 data is here! 

Similar to Year-1 and Year-2, Prime’s Health Outcomes team recently released its Year-3 real-world study, continuing to explore the impact of adherence trends in individuals without diabetes using GLP-1s for obesity. We expect this next phase to generate strong interest across clients, media and the broader health care industry. We look forward to contributing continued insights into this important and evolving area of health care.