OBJECTIVES: Dual Medicare and Medicaid enrollees with cancer represent a clinically and financially vulnerable subgroup of patients in the U.S. for whom management of comorbid conditions is an ongoing challenge. In 2006, Medicare Part D drug coverage removed restrictions on the number of reimbursable prescriptions per month (drug caps) for many of these patients. This study evaluated the impact of the removal of drug caps on the use of effective non-cancer treatments overall and by race (black vs. white). METHODS: We used a quasi-experimental interrupted time series with comparison series design and a representative 5% national sample of non-institutionalized, continuously enrolled dual enrollees with evidence of breast, colorectal, prostate, lung, or cervical cancer during the study period (2004-2007). We examined medication use between 24 months before and 24 after transition from Medicaid drug coverage (with or without drug caps) to Part D drug coverage on January 1, 2006. We estimated changes in prevalence and intensity of use (in days' supply) of antidepressants, antihypertensives, and lipid lowering agents after cap removal, overall and by race. RESULTS: The removal of caps was associated with greater intensity of use for lipid lowering medications among dual enrollees with cancer overall (days’ supply: 3.63; 95% CI: 1.57, 5.70). Among blacks, increases were detected in the use of lipid lowering therapy (days’ supply: 4.01; 95% CI: 2.92, 5.09) and antidepressant use (days’ supply: 2.20; 95% CI: 0.61, 3.78). Increases were not detected among whites. Small sample sizes did not permit stratification of these models by medical need, severity or cancer type. CONCLUSIONS: The removal of drug caps was associated with increases in the use of lipid lowering medications among dual enrollees with cancer, particularly among blacks. The clinical implications of these changes in utilization are not well understood and deserve further investigation.