Tehran University of Medical Sciences Journal of Pharmaceutical Care 2322-4630 13 2 2025 06 30 83 92 EN Marzieh Shahrabi Department of clinical pharmacy, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran Tahereh Sorbi Department of Anesthesiology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran Sina SeyedImani Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran Haleh Rezaei Department of clinical pharmacy, Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran Zahra Mousavi Department of Psychiatry, School of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran Mohammad Solduzian Pain Research Center, Department of Anesthesiology and Pain Medicine, Iran University of Medical Sciences, Tehran, Iran 2025 01 16 2025 04 30 Background: Major depressive disorder (MDD) and generalized anxiety disorder (GAD) are among the most common mental disorders contributing to sleep disturbance. Given the decline in sleep quality of these patients, improving sleep may be addressed alongside other treatment strategies. This study evaluated the effect of melatonin on improving sleep quality in patients who were diagnosed with MDD or GAD. Methods: Seventy-eight patients diagnosed with MDD or GAD were randomly assigned to two groups, including the intervention group, which received oral melatonin 3 mg daily for four weeks and the control group, which received only placebo. Assessments were made by the Groningen Sleep Quality Scale (GSQS) and Pittsburgh Sleep Quality Index (PSQI) questionnaire at the beginning and after four weeks using SPSS software. Results: The mean age of patients was 38.78±14.12 years. There was no significant difference between the two groups in terms of demographic data. According to the analysis, although the change in GSQS scores between the placebo and melatonin groups was not significantly different from baseline scores, the difference in PSQI scores before and after the use of melatonin was significant (P=0.01). There was also a significant difference regarding the GSQS score between the two groups before and after the intervention (P=0.04). Conclusion: The present study illustrated that melatonin use for one month could improve the quality of sleep among MDD and patients with GAD to some degree; however, according to the PSQI and GSQS scoring, there is no credible evidence that shows a significant improvement in the sleep quality of our study population. https://jpc.tums.ac.ir/index.php/jpc/article/view/795 https://jpc.tums.ac.ir/index.php/jpc/article/download/795/418