CVS Caremark formulary change linked to brief rise in GLP-1 switching | AMCP Annual 2026

A May 2025 formulary decision by CVS Caremark to drop Zepbound (tirzepatide) from its preferred formulary and instead give that position to Wegovy (semaglutide) led to a sharp but short-lived rise in patient switching, with prescribing patterns settling back down within a few months, according to an abstract presented at this year’s AMCP Annual Meeting in Nashville.

GLP-1 receptor agonists are widely used to treat type 2 diabetes and obesity and can help improve blood sugar control, support weight loss and lower cardiovascular risk. Demand for GLP-1s has grown quickly in the U.S., making them one of the highest-cost drug classes for employers and health plans as use expands beyond diabetes into obesity treatment, according to data from IQVIA.

As spending rises, insurers and pharmacy benefit managers (PBMs) are using tools such as formulary design, step therapy and prior authorization to help manage costs and guide use within drug classes, according to frameworks noted by AMCP.

These coverage strategies can influence which drugs are used and how often they are prescribed based on coverage rules and patient out-of-pocket costs. Because GLP-1s are considered highly effective treatments for these conditions, formulary decisions involving drugs such as tirzepatide and semaglutide are closely watched, as they can affect patient access and prescribing patterns.

Back when CVS Caremark announced it would remove tirzepatide from its preferred formulary and instead favor semaglutide starting July 1, 2025, it marked a major change in coverage for these treatments. Researchers from Truveta studied this policy change to look at its impact on patient switching and prescribing trends.

According to the company’s website, Truveta is a health data platform that provides large-scale, regularly updated electronic health record (EHR) data from U.S. health systems for research and analysis.

Using data from Truveta, researchers analyzed two groups of patients: the first included adults ages 18 and older with a body mass index of 27 or higher who had two consecutive fills for a GLP-1 between January and September 2025. Switching was defined as having an active supply of a different GLP-1 drug in back-to-back months.

The second analysis examined prescribing trends for these drugs from January 2024 through September 2025, measuring each medication’s share of total prescriptions.

The overall study included 700,907 patients. It was found that before May 2025, switching from tirzepatide was low at about 0.6% per month, but it rose to 10.2% between June and July, marking a 17-fold increase.

Out of those who switched, 82.4% transitioned to semaglutide. After July, switching rates dropped but remained above baseline at 1.8% through September.

Across 1.84 million patients and 7.1 million prescriptions, tirzepatide use had been increasing steadily before the formulary change, but growth slowed after July before increasing again in September. Semaglutide saw its largest one-month gain between June and July and then remained mostly stable afterward.

Based on study methods and results, a key strength of the study includes the use of large-scale, real-world data from Truveta, which allowed researchers to track both switching behavior and prescribing trends over time in a large national population. The study also captured patterns before and after a clearly defined formulary action, helping show how quickly utilization can shift in response to payer policy.

However, the findings may be affected by factors such as 90-day prescription fills, which could delay observed switching and make short-term estimates less precise.

The researchers noted that continued monitoring will be important to understand whether these changes continue or reflect short-term disruption following the formulary update.