Importance: Atypical antipsychotics (AAPs) are often used off-label to manage dementia-associated neuropsychiatric symptoms. In 2005, the US Food and Drug Administration (FDA) issued a boxed warning for the use of AAPs in elderly patients. The long-term association of this warning with health outcomes is unknown to date. Objective: To assess the long-term association of the 2005 FDA boxed warning on AAPs with psychiatric medication and opioid use, health events, and quality of life among elderly individuals with dementia. Design, Setting, and Participants: For this cross-sectional study, data were analyzed from the household component of the Medical Expenditure Panel Survey (MEPS), the National Ambulatory Medical Care Survey (NAMCS), and the National Hospital Ambulatory Medical Care Survey (NHAMCS) fielded between January 1, 1996, and December 31, 2014. This interrupted time-series analysis applied to 3-year moving means derived from the 1996-2014 MEPS, NAMCS, and NHAMCS. All survey respondents included in this analysis were 65 years or older and had dementia. Data analysis was performed from December 1, 2017, to March 15, 2018. Exposures: The 2005 FDA boxed warning on AAPs. Main Outcomes and Measures: Use of psychiatric medications and opioids, prevalence of cerebrovascular and cardiovascular events, prevalence of falls and/or fractures, 2-year mortality, and health-related quality of life assessed by the Medical Outcomes Study 12-Item Short-Form Health Survey scores. Results: A total of 2430 (MEPS) and 5490 (NAMCS and NHAMCS) respondents were identified, corresponding to weighted populations of 22 996 526 (MEPS) and 65 502 344 (NAMCS and NHAMCS) noninstitutionalized elderly individuals with dementia (mean [SD] age, 81.06 [1.13] years; 63.1% female). In the MEPS sample, compared with before 2005, AAP use (from an annual slope of 0.99 to -0.18 percentage points), cerebrovascular events (0.75 to -0.50 percentage points), and falls and/or fractures (-1.72 to -0.40 percentage points) decreased and opioid use (0.04 to 1.29 percentage points), antiepileptic use (-0.42 to 1.21 percentage points), cardiovascular events (-0.13 to 1.30 percentage points), and 2-year mortality risk (-0.68 to 0.18 percentage points) increased. Health-related quality of life remained relatively unchanged. The NAMCS and NHAMCS sample yielded similar findings. Conclusions and Relevance: These data suggest that the 2005 FDA boxed warning was associated with some unintended negative patient outcomes.