Objective: To investigate whether patients who use mail-order pharmacies were more likely to have good medication adherence than patients who use local pharmacies.

Study design: Cross-sectional investigation.

Methods: We conducted cross-sectional analyses of patients from the Kaiser Permanente Northern California (KPNC) diabetes registry who received a new antiglycemic, antihypertensive, or lipid-lowering index medication between January 1, 2006, and May 31, 2006. We defined good adherence as medication availability at least 80% of the time (ie, a continuous measure of medication gaps value of < or = 20%) and compared adherence between mail-order users (> or = 66% of refills by mail) and KPNC local pharmacy users (all refills in person). Adherence was calculated from the initial dispensing through 15 months of follow-up, medication discontinuation, or May 31, 2007, whichever came first. We analyzed the data using multivariate logistic regression models, after determining that unmeasured patient-level factors and self-selection did not significantly bias our analyses.

Results: A total of 13,922 eligible patients refilled an index medication. Compared with those who used only local KPNC pharmacies, patients who received medications by mail were more likely to have good adherence (84.7% vs 76.9%, P <.001). After adjusting for potential confounders, including days' supply and out-of-pocket costs, mailorder users had better adherence to antiglycemic, antihypertensive, and lipid-lowering medications (P <.001 for all).

Conclusions: Compared with patients who obtained medication refills at local pharmacies, patients who received them by mail were more likely to have good adherence. The association between mail-order use and medication adherence should be evaluated in a randomized clinical trial.