Truveta links CVS formulary change to 9.6% Zepbound switching rate in July 2025

A July surge in patients leaving anti-obesity tirzepatide — the drug sold as Zepbound — offers the clearest measure yet of how a coverage decision can move people between molecules, according to an analysis Truveta Research published September 5, 2025 ^[1]. The share of patients with an active supply of the drug who switched to a different GLP-1 reached 9.6% in July, better than 16 times the rate seen on average earlier in the year ^[1].

CVS Caremark announced on May 1, 2025 that Zepbound would leave its standard preferred formulary for obesity on July 1, with Wegovy, the obesity brand of semaglutide, taking the preferred slot ^[1]. The change touched only the obesity indication; the same molecule stayed on the list as Mounjaro for type 2 diabetes ^[1].

Truveta drew on 609,406 patients aged 18 and older with a body mass index above 27 and at least one GLP-1 fill between January and July 2025 ^[1]. Slightly more than half were 45 to 60 years old (52.2%), 62.2% were female and 54.8% had type 2 diabetes ^[1]. A switch was counted when a patient had an active supply of one GLP-1 in a month and an active supply of a different one the following month ^[1].

Earlier in 2025 the churn was small. From January through April, 0.6% of anti-obesity tirzepatide users and 2.3% of anti-obesity semaglutide users moved to another drug in an average month ^[1]. Over those same months, 99.4% of patients with an active supply of anti-obesity tirzepatide in one month still had it the next ^[1].

June to July looked different. Of patients with an active supply of anti-obesity tirzepatide in June, 90.4% were still on it in July, 8.0% had moved to anti-obesity semaglutide and 0.9% had gone to the diabetes formulation of tirzepatide ^[1]. Among everyone who switched, 82.8% landed on anti-obesity semaglutide ^[1]. Movement away from semaglutide fell during the same window ^[1]. Counting every GLP-1 studied, 6.6% of patients made at least one switch during the seven months ^[1].

Truveta cautioned that the timing overlaps with the formulary change but does not prove it drove individual decisions. Supply problems, regional insurance rules and prescriber habits could also have played a part, the researchers wrote ^[1]. The analysis captured neither patients' insurers nor anyone who stopped treatment instead of switching, so the total disruption may be larger than the numbers show ^[1]. The findings are preliminary, have not been peer reviewed and reflect data pulled August 27, 2025 ^[1].

Why it matters for patients

CVS Caremark handles prescription benefits for 25 million to 30 million Americans, a pool large enough that one formulary decision can shape what tens of millions of people are offered ^[1]. Under the change, someone on Zepbound may need to move to Wegovy to keep coverage, while staying on Zepbound may mean paying more out of pocket or being denied coverage, according to Truveta ^[1]. Patients who do switch may notice differences: in clinical trials the tirzepatide obesity drug produced more weight loss than the semaglutide obesity drug, the researchers noted ^[1]. The change can also add steps, since alternatives and exception requests have to be worked through ^[1]. The figures cover switching only. How many people simply stopped, and how many sought exceptions, has not been reported.

What happens next

Truveta said more switching is likely in the months ahead, partly because fills that run longer than 30 days can delay when a change shows up in the data ^[1]. The analysis runs through July 2025, with data accessed August 27, 2025 ^[1]. Whether the pace has held, slowed or grown since then has not been disclosed.