OBJECTIVES: The approaching availability of lower-cost generic angiotensin receptor blockers (ARBs) may affect formulary policies by encouraging patients responding well to ARB valsartan to switch to another ARB with lower prescription costs. Thus, this study aims to estimate the economic impact of switching from valsartan (including valsartan-based single pill combinations) to other ARBs without apparent medical reasons.  METHODS: Patients with essential hypertension and at least six months of continuous valsartan treatment, free of hospitalization, cardiovascular events, renal events or ARB-associated adverse events were identified from the large administrative claims database MarketScan from January 1, 2004 to March 31, 2008. Those who subsequently switched to a different ARB with at least a 5% copayment decrease (switchers) were matched to those who did not switch (maintainers) according to propensity score quintiles and selected baseline characteristics. Matched switchers and maintainers were compared in terms of medication discontinuation, healthcare resource use and costs during the 6 months following the index fill.  RESULTS: A total of 99,926 valsartan maintainers and 2,150 switchers (with a mean copayment decrease of $16.5 per month) were identified and matched. After matching, switching from versus maintaining valsartan was associated with an 8% higher risk of medication discontinuation (P<0.008), 19.1 additional outpatient visits/100 patients (P=0.002) and 9.3 additional hypertension-related inpatient days/100 patients (P=0.030).  Concurrently, switching from versus maintaining valsartan was associated with higher total medical costs by $748/patient (P<0.001), driven largely by higher costs for hypertension-related medical services by $492/patient (P=0.004). CONCLUSIONS: Hypertension patients maintained on valsartan who switched to a different ARB with a lower copayment experienced substantial increases in medication discontinuation, healthcare resource use and costs compared to those who maintained valsartan treatment. Formulary policies that encourage such non-medical switching may therefore lead to increased total costs.