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This study investigated whether dosing frequency affects antipsychotic medication adherence among patients with schizophrenia.Databases from the Department of Veterans Affairs were used to assess adherence among patients with a diagnosis of schizophrenia. Adherence was measured by using antipsychotic medication possession ratios (MPRs). Adherence was compared among patients who experienced an increase or decrease in dosing frequency and among patients on stable regimens of once-daily or more than once-daily dosing.Among patients with a dose increase (N=1,639), those with increases in dosing frequency (N=258) had a mean change in MPRs of -.105, compared with -.002 for those without a dosing frequency change (N=1,381) (p<.001). Patients with decreases in dosing frequency (N=1,370) had a small but significant increase in mean MPRs (MPR change=.045) when compared with 2,740 patients without a dosing frequency change (MPR change=-.018) (p<.001). Among patients on stable regimens (N=32,612), there were no significant differences in MPRs between those receiving once-daily dosing (MPR=.80) and those receiving more than once-daily dosing (MPR=.80).Among patients on less stable dosing regimens, increases in dosing frequency may result in modest decreases in adherence.