Study design. Cases were defined as patients who started taking fixed-dose combination (FDC) drugs within the time window. The index date was defined as the date of first prescription within the time window of FDC for cases and of ARB for controls. The total and antihypertensive drug costs were calculated before and after the index date and were compared in cases and controls. A difference-in-differences (DID) approach was used to estimate the effect on annual costs of switching to FDC drugs.