Dementia Care in Nursing Homes (hereafter referred to as the partnership) was established to improve the quality of care for patients with dementia, measured by the rate of antipsychotic prescribing. OBJECTIVE To determine the association of the partnership with trends in prescribing of antipsychotic and other psychotropic medication among older adults in long-term care. DESIGN, SETTING, AND PARTICIPANTS This interrupted time-series analysis of a 20% Medicare sample from January 1, 2009, to December 31, 2014, was conducted among 637 426 fee-for-service Medicare beneficiaries in long-term care with Part D coverage. Data analysis was conducted from May 1, 2017, to January 9, 2018. MAIN OUTCOMES AND MEASURES Quarterly prevalence of use of antipsychotic and nonantipsychotic psychotropic medications (antidepressants, mood stabilizers [eg, valproic acid and carbamazepine], benzodiazepines, and other anxiolytics or sedative-hypnotics). RESULTS Among the 637 426 individuals in the study (446 538 women and 190 888 men; mean [SD] age at entering nursing home, 79.3 [12.1] years), psychotropic use was declining before initiation of the partnership with the exception of mood stabilizers. In the first quarter of 2009, a total of 31 056 of 145 841 patients (21.3%) were prescribed antipsychotics, which declined at a quarterly rate of-0.53% (95% CI,-0.63% to-0.44%; P < .001) until the start of the partnership. At that point, the quarterly rate of decline decreased to-0.29% (95% CI,-0.39% to-0.20%; P < .001), a postpartnership slowing of 0.24% per quarter (95% CI, 0.09%-0.39%; P = .003). The use of mood stabilizers was growing before initiation of the partnership and then accelerated after initiation of the partnership (rate, 0.22%; 95% CI, 0.18%-0.25%; P < .001; rate change, 0.14%; 95% CI, 0.10%-0.18%; P < .001), reaching 71 492 of 355 716 patients (20.1%) by the final quarter of 2014. Antidepressants were the most commonly prescribed medication overall: in the beginning of 2009, a total of 75 841 of 145 841 patients (52.0%) were prescribed antidepressants. As with antipsychotics, antidepressant use declined both before and after initiation of the partnership, but the decrease slowed (rate change, 0.34%; 95% CI, 0.18%-0.50%; P < .001). Findings were similar when limited to patients with dementia. CONCLUSIONS AND RELEVANCE Prescribing of psychotropic medications to patients in long-term care has declined, although the partnership did not accelerate this decrease. However, the use of mood stabilizers, possibly as a substitute for antipsychotics, increased and accelerated after initiation of the partnership in both long-term care residents overall and in those with dementia. Measuring use of antipsychotics alone may be an inadequate proxy for quality of care and may have contributed to a shift in prescribing to alternative medications with a poorer risk-benefit balance.