Background and Objective: Bipolar I disorder is characterized by severe mood fluctuations and cognitive deficits that can significantly impair patients' daily functioning. False memory, as a complex cognitive phenomenon, may play an important role in reducing patients' ability to perform everyday activities. This study aimed to investigate the relationship between false memory and daily functioning in patients with bipolar I disorder.

Methodology: This research was a descriptive-correlational study. The statistical population included all patients with bipolar I disorder hospitalized in Zare Psychiatric and Burns Hospital in Sari, Iran, during spring 2025. The sample size was determined as 36 patients, selected through non-random convenience sampling. The DRM (Deese-Roediger-McDermott) test (test-retest reliability coefficient = 0.86) was used to assess false memory. Daily functioning was evaluated using the Social and Occupational Functioning Assessment Scale (SOFAS) (Cronbach's alpha = 0.85). Data were analyzed using Pearson correlation coefficient and multiple regression analysis with SPSS version 29.

Findings: Results showed a significant inverse correlation between false memory and daily functioning (r = -0.44, p = 0.008). Moreover, false memory could predict 23% of the variance in daily functioning (R² = 0.23, p = 0.022). Patients in the manic phase exhibited the highest level of false memory (mean = 4.1) and the lowest daily functioning (mean = 58.3), whereas patients in the euthymic phase showed the best daily functioning (mean = 66.8) and the lowest false memory (mean = 3.2).

Conclusion: The findings of this study confirm that false memory has a negative relationship with daily functioning in patients with bipolar I disorder. Memory errors can impair patients' ability to perform daily tasks, social interactions, and maintain individual independence. Therefore, designing targeted cognitive interventions to reduce false memory errors may help improve daily functioning and quality of life in these patients.