Introduction Poor medication adherence in people with bipolar disorder (BD) is common. Younger age is a reported risk factor for medication non-adherence in individuals with BD. The literature on the relationship between adherence and symptoms is conflicting. Additionally, self-stigma in BD patients is well-documented, and could have negative effects on self-care that includes medication treatments. Stigma experienced by BD patients may have implications on quality of life, social dysfunction, and suicidality. Lastly, while previous analysis demonstrates that a customized adherence enhancement (CAE) program targeted to mixed-age poorly adherent patients with BD increases medication adherence and functional status compared to a rigorous BD-specific educational (EDU) program, how specific adherence promotion efforts improve adherence in relation to patient age has not been studied. This secondary analysis from a completed randomized controlled trial (RCT) comparing two interventions in poorly adherent patients with BD evaluated medication adherence, psychiatric symptom severity, functional status, and internalized stigma levels in older (age ≥55 years old) vs. younger (age <55 years old) adults at baseline and over time. Given demographic changes that project an increase in both proportions and absolute numbers of people with serious mental illnesses such as BD, findings may have practical implications for clinical care. Methods Data for this analysis derived from a prospective six-month NIMH-funded RCT comparing a CAE intervention intended to promote BD medication adherence with EDU in 184 poorly-adherent individuals with BD. We chose an age 55 cut-off to differentiate younger (n=144) vs. older (n=40) subgroups within the sample, consistent with a recent consensus recommendation to consider that people with BD on average lose one to two decades of life compared to the general population. Medication adherence was measured with the Tablets Routine Questionnaire (TRQ). BD symptoms were measured using the Montgomery–Åsberg Depression Rating Scale (MADRS), the Young Mania Rating Scale (YMRS), and the Brief Psychiatric Rating Scale (BPRS). Participants were also rated with Clinical Global Impression—Bipolar Version (CGI-BP). Global Assessment of Functioning (GAF) was used to measure functional status. Attitudes regarding self-stigma were assessed with the Internalized Stigma for Mental Illness scale (ISMI). To evaluate for age-related differences in change over time in TRQ, BPRS, and GAF in the entire sample, treatment arms were combined and younger vs. older subgroups were compared. Mann-Whitney U was used to analyze non-parametric continuous variables, chi-square for categorical variables, and t-test for normally distributed continuous variables. In analysis with very small N comparisons, Fisher's exact test was used. To evaluate for age-related differences in change over time in TRQ, BPRS, and GAF in each treatment arm, mixed longitudinal models were fit. Covariates included main effects for age, treatment, and time, as well as three-way interaction terms involving age, treatment, and time. Results BASELINE FINDINGS In our sample, older participants had significantly lower anxiety disorder comorbidity compared to younger participants, considering participants with one or more (56.4% vs. 78.4%) and two or more anxiety disorders (41.0% vs. 57.5%). There were no statistically significant differences in past-week and past-month adherence with BD medications between older and younger participants (past week TRQ: 37.2 vs. 43.0; past month TRQ: 38.5 vs. 40.8). There were no significant differences in YMRS, BPRS, and GAF scores between the two groups. Older adults had significantly lower MADRS scores than their younger counterparts (14.9 vs. 18.9, p=0.011) and significantly lower CGI-BP (3.08 vs. 3.47, p=0.025), indicating comparatively lower depressive and overall symptom severity. Older adults had significantly lower ISMI scores than their younger counterparts (61.95 vs. 69.27, p=0.001), indicating relatively lower internalized stigma. These findings remained significant in four of five ISMI subscales: alienation (p=0.017), stereotype endorsement (p=0.002), discrimination experience (p=0.001), and social withdrawal (p=0.013). Only age-related differences in the subscale of stigma resistance were not significant (p=0.450). LONGITUDINAL FINDINGS In the combined group (CAE plus EDU), evaluation over time showed no significant difference between older and younger participants in TRQ, BPRS, and GAF. There were no significant findings and no interaction between time and age group when analyzed globally, regardless of treatment arm assignment at baseline. In analysis evaluating for change over time between older and younger participants by treatment arm, for TRQ, there was a significant finding of interaction between time, age group, and treatment arm (p = 0.007) such that there was a trend for older individuals to have worse adherence over time in the EDU vs. the CAE intervention arm. For BPRS and GAF, there were no significant findings and no interaction between time, age group, and treatment arm. Conclusions This secondary analysis from an RCT comparing two interventions in poorly adherent patients with BD found that older adults may be less depressed and anxious, with less self-stigma compared to younger people with BD and poor adherence. CAE is a behavioral intervention that may yield sustained benefit with respect to medication adherence in adults with BD who are age 55 and older. This research was funded by Research reported in this poster was supported by the National Institute of Mental Health of the National Institutes of Health under Award Number R01MH093321. Support was also received from the Clinical and Translational Science of Cleveland, UL1TR000439 from the National Center for Advancing Translational Sciences (NCATS) component of the National Institutes of Health and NIH roadmap for Medical Research. [ABSTRACT FROM AUTHOR]