Truveta publishes data on what the CVS switch did to prescribing

Truveta Research published data on September 5, 2025 showing that prescribing patterns for two popular weight-loss drugs shifted sharply in the month after CVS Caremark changed its coverage rules. The analysis, based on records for 1,647,238 patients and more than 6 million GLP-1 receptor agonist prescriptions from January 2024 through July 2025, found that growth in tirzepatide prescribing for obesity slowed by roughly half while semaglutide prescribing for obesity jumped by its largest one-month margin in the study period ^[1].

CVS Caremark, which manages prescription benefits for an estimated 25 to 30 million Americans, announced on May 1, 2025 that it would remove tirzepatide sold for weight loss (Zepbound) from its standard preferred formulary starting July 1, 2025, making semaglutide sold for weight loss (Wegovy) the preferred option instead ^[1]. The change applies only to the obesity indication; tirzepatide sold as Mounjaro for type 2 diabetes was not affected ^[1].

Before the change, tirzepatide prescribing for obesity had been climbing steadily, averaging a 0.06 percentage-point increase each month from January 2024 through June 2025, and it had overtaken semaglutide by late 2024, reaching 1.2% of all prescriptions by May 2025, nearly double semaglutide's rate at the time ^[1]. From June to July 2025, however, that growth slowed to just 0.03 percentage points, the smallest monthly gain in the period studied ^[1]. Semaglutide prescribing for obesity, which had been rising by only about 0.02 percentage points a month, jumped by 0.1 percentage points in that same window, its largest single-month gain in the entire 19-month dataset ^[1].

The pattern held for first-time prescriptions too. Tirzepatide initiations for obesity, which had grown 239% cumulatively from January 2024 to June 2025, dipped slightly from June to July, the first monthly decline in nearly a year, aside from a holiday-related dip in December 2024 ^[1]. Semaglutide initiations, which had actually fallen 31% from their mid-2024 peak through June 2025, rose 4.9% from June to July, the strongest monthly gain in over a year ^[1].

Why it matters for patients

The timing lines up with the formulary switch, but Truveta researchers were careful to say their analysis does not prove the coverage change caused the shift ^[1]. Other factors, including drug supply, regional insurance rules, or doctors' own preferences, could also be at play ^[1]. Still, the data suggest that when a large pharmacy benefit manager changes which drug it prefers, prescribing patterns can move within weeks, even for medications in high demand ^[1].

For patients on tirzepatide for obesity through CVS Caremark coverage, this means some may be facing a choice between switching to semaglutide to keep insurance coverage or paying more out of pocket to stay on tirzepatide ^[1]. The report also notes that a prescription does not guarantee a filled prescription; some patients may get a new prescription but be unable to fill it due to cost-sharing or pharmacy barriers ^[1]. A companion Truveta report used actual dispensing data, rather than prescriptions, to look more directly at how many patients switched drugs during this period ^[1].

What happens next

Truveta's findings run only through July 2025, one month after the formulary change took effect, so it is not yet known whether the slowdown in tirzepatide growth and the jump in semaglutide growth will continue, reverse, or level off in the following months ^[1]. The findings are described as preliminary and have not been peer reviewed ^[1].