Background: Older patients with dementia are often unable to take their medications as prescribed due to cognitive and physical impairment. Objectives: To review the evidence on medication adherence in older patients with dementia in terms of the level of adherence, outcomes, contributing factors, and available interventions. Methods: A systematic literature review was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Searched databases included CINAHL, Cochrane Library, DARE, MEDLINE, and PubMed. Results: Eighteen studies reported levels of medication adherence or discontinuation and related factors. Medication adherence ranged from 17% to 42%, and medication discontinuation before the end of treatment ranged from 37% to 80%. Nonadherence was associated with an increased risk of hospitalization or death, while increasing age, choice of medication, use of concomitant medications, and medicines’ costs were reported to decrease medication adherence. Telehealth home monitoring and treatment modification were the only interventions reported in the literature to improve medication adherence in this population. Conclusion: Older patients with dementia have a low level of medication adherence. Future research should focus on the development and implementation of interventions to help older patients with dementia and their caregivers make better use of medications.