Does Sovaldi have an adherence problem, or are doctors just holding off in anticipation of the next big thing? According to CVS Health Research Institute, which analyzed discontinuation rates for Gilead’s super-blockbuster hep. C drug, a bit of both are at play.

The pharmacy company released the findings Wednesday, saying that it’s observed a downward trend in patients taking the HCV medication.

The analysis followed 1,965 patients, all of whom were managed by the firm’s PBM CVS/caremark and who began taking Sovaldi from its approval in December 2013 to August 2014. During that time, researchers found that 8.1% of patients stopped taking the drug before finishing the regimen (prior to 12 weeks). While that number may not seem high on its own, it is quadruple what was observed in Sovaldi clinical trials.

The chief medical officer of CVS Health, Troyen Brennan, M.D., said in a statement that although the “simplicity” of the Sovaldi regimen is conducive to adherence—and that another peak in spending for hep. C drugs may come upon release of Gilead’s forthcoming all-oral treatment—the drug may still benefit from additional patient-support programs so that patients derive full benefit.

Patients taking Sovaldi with the maximum amount of concurrent medications saw the highest discontinuation rates. A total of 10.2% of patients taking Sovaldi+peginterferon+ribavirin discontinued, compared to the 4.2% of patients who didn’t refill their prescription of Sovaldi+Olysio, while Sovaldi+ribavirin saw a 9% discontinuation rate. (Olysio is Johnson & Johnson’s HCV med.)

Across all regimens, treatment-naïve patients—first time users—unsurprisingly saw the greatest need for adherence efforts, as the group was 64% more likely to discontinue therapy with Sovaldi than treatment-experienced patients.

While those new to treatment may have difficulty staying on track, the report states that they aren’t the only force driving down refills. Hepatologists may also be warehousing patients in preparation for Gilead’s awaited, all-oral single-pill therapy of Sovaldi and ledipasvir, which Gilead filed with US regulators in February.

AbbVie’s drug combo too is awaiting approval. In April, the drugmaker submitted an NDA for an all-oral regimen, which also recently received Breakthrough Therapy designation.