Background: Dengue fever can present with symptoms that mimic drug-related reactions, especially in patients with complex medical histories, such as those with bipolar disorder on multiple medications. Case details: We report a 62-year-old female with a known history of bipolar disorder who was admitted with altered mental status, vomiting, and a rash. Given her psychiatric treatment, there was an initial concern for a drug-related reaction. Investigations: Through investigation was conducted. Results revealed a positive serology for dengue fever, alongside leukopenia and thrombocytopenia. Discussion: This case highlights the diagnostic challenge of differentiating between adverse drug reactions and infectious diseases like dengue in patients on multiple medications. Conclusion: Clinicians must maintain a high index of suspicion for tropical diseases like dengue, particularly in patients with complex comorbidities. This case underscores the importance of comprehensive evaluations in emergency settings and the need for a broad differential diagnosis approach.