Medication nonadherence remains a significant barrier to the optimal management of chronic cardiovascular diseases, leading to increased morbidity and health care costs [1]. Digital interventions, particularly text-based nudges, are potential strategies for enhancing medication adherence [2-5]. The Nudge study (NCT 03973931) compared the effectiveness of three different text-based interventions versus usual care to improve medication adherence among patients with documented medication refill gaps (time between medication supply end and the next refill) [6]. There was no difference in adherence (assessed by proportion of days covered [PDC]) at 12 months between any of the intervention groups and usual care [6].

While the main Nudge study results were null [6], prior studies suggest patient engagement in mHealth interventions is critical to their success [2,7,8]. We conducted this secondary analysis to assess whether greater engagement with the text messaging interventions was associated with improved medication adherence at 12 months. We hypothesized that patients who replied to study texts would have higher medication adherence defined by a shorter gap length between medication refills and higher refill adherence.

A total of 9501 patients were enrolled; 9269 had complete follow-up data (the CONSORT diagram has been published previously [6]). After excluding 2321 usual care patients, we analyzed 6948 individuals; 3262 (46.9%) responded to an intervention message. Among the 3262 responders, 456 (14%) opted out, 843 (25.8%) provided other responses and 1963 (60.2%) provided standard responses. Patients who engaged with the messages, particularly standard responders, differed significantly from nonresponders, with engagement more likely among those in certain health care systems or on fewer medications (Table 1).

Patients who engaged with the texts, regardless of response type, had a shorter gap length compared to patients who did not respond. In addition, patients who responded to any messages had a higher adherence at 12 months, which persisted after the adjustment for demographics and clinical characteristics (Table 2).

This secondary analysis assessed the association between engagement and medication adherence in a text messaging clinical trial. We enrolled a diverse patient population including a large proportion of Hispanic and Spanish-speaking patients as well as patients who are traditionally medically underserved (ie, receiving care at federally qualified health centers and veterans affairs centers). Overall, 47% of intervention arm patients engaged with texts. Any engagement was associated with shorter medication gap lengths, and higher medication adherence at 12 months. While our participants included diverse and traditionally underserved patients, these findings may not be generalizable to patients without access to or comfort with text messaging, who would have been ineligible for the parent trial.

Another potential limitation lies in our response classification criteria. Patients who submitted nonstandard responses were placed exclusively in the “Other Response” group, which may conflate ambiguous interactions with more meaningful engagement. Furthermore, we cannot determine causality between engagement and adherence given this post-hoc analysis.

Our findings are consistent with prior literature highlighting the importance of patient engagement in mHealth interventions to improve adherence and self-management [2-5]. Collectively, these findings suggest that patient engagement is a strong marker for, and is closely associated with, higher medication adherence.