BACKGROUND: Statins have been shown to be effective in reducing the occurrence of cardiovascular (CV) events and are widely prescribed for the risk reduction of CV diseases and recurrent CV events. However, poor adherence prevents some patients from receiving the maximum benefit of the therapy. Motivational interviewing (MoI) is a patient-centered collaborative approach that can be used to improve medication adherence. Group-based trajectory modeling depicts patterns of adherence over time and may help tailor the MoI intervention to further enhance adherence. OBJECTIVE: To assess the effect of a phone-based MoI intervention tailored by patients’ past adherence trajectory in improving adherence to statins among patients in a Medicare Advantage prescription drug plan (MAPD). METHODS: Patients continuously enrolled in an MAPD from 2013 to 2017 with a statin prescription between January and June 2015 to allow 2 years of pre-index period and 1 year of follow-up were included in the study. Adherence to statins was measured monthly during the 1-year follow-up as proportion of days covered (PDC) and incorporated into a group-based trajectory model to provide 4 distinct patterns of adherence: adherent, rapid decline, gradual decline, and gaps in adherence. Patients in the 3 nonadherent groups were randomized to either control or intervention. The intervention was an initial counseling call and up to 2 monthly followup calls by pharmacy students trained in MoI, providing education consistent with a previously identified pattern of use. Refill data at 6 months post-intervention were evaluated to examine the intervention’s effect on PDC, as continuous and dichotomized as PDC≥0.8, as well as discontinuation. Multivariable regression adjusted for baseline demographics, clinical characteristics, and past adherence trajectory. RESULTS: There were 152 patients included in the analysis who received MoI phone calls and 304 randomly selected controls. Mean PDC for the intervention group (0.67±0.3) was significantly higher than the control (0.55±0.4; P<0.001). The intervention group was also less likely to discontinue (OR=0.38; 95% CI=0.19-0.76) and more likely to be adherent in the linear regression model (β=12.4; P<0.001) as well as in the logistic regression model (OR=1.87; 95% CI=1.18-2.95). Previous adherence trajectories were significantly associated with adherence in the follow-up. CONCLUSIONS: Patients who received the MoI intervention were more likely to be adherent and less likely to discontinue the statin in the 6 months follow-up compared with controls. Future research can identify other approaches to tailor interventions and expand the intervention to other languages. This intervention may also prove valuable to improve adherence to other medications for chronic and asymptomatic diseases.