Background: Older patients with breast cancer represent a vulnerable population at higher risk of experiencing distress and pain, as well as medication-related adverse events from pharmacological treatment of these symptoms. The purpose of this study is to estimate the prevalence of psychotropic (anxiolytic, antidepressant, and antipsychotic) and opioid medication use by older women diagnosed with breast cancer. Methods: This population-based cohort study followed 19,353 women older than 65 years diagnosed with incident, nonmetastatic breast cancer in Quebec, Canada. Data were obtained from provincial, universal health and drug insurance plans covering all medical and pharmaceutical care. Descriptive statistics were calculated for demographic information, breast cancer characteristics, and treatments. Psychotropic and opioid medication use was assessed across the care trajectory: precancer baseline, active care, and first-year survivorship. Results: There was a marked increase in the prevalence of medication use from precancer baseline to active care, followed by a decrease into first-year survivorship. Anxiolytics were used most often across the care trajectory (36.3%, 50.6%, and 44.4% at baseline, active care, and survivorship, respectively). In contrast, antipsychotic and opioid medications were sought primarily during active care (4.5- and 7-fold increases from baseline, respectively), with opioid use during active care increasing dramatically over the study period (9.0% to 40.9% from 1998 to 2010). Unlike other drugs, antidepressant use peaked in active care but persisted into survivorship (14.7%, 22.4%, and 22.3% at baseline, active care, and survivorship, respectively). Conclusions: A substantial proportion of older patients with breast cancer use psychotropic and opioid medications. The different patterns of medication use represent distress and pain experienced by patients across the care trajectory. Given that medication use in this vulnerable population is associated with an increased risk of adverse events, a multidimensional approach integrating psychological interventions in cancer care may better address psychosocial needs of older patients with breast cancer.