Evaluating the Effect of Melatonin on Positive and Negative Symptoms of Schizophrenic Patients: A Randomized Placebo-Controlled Study

Objective: Schizophrenia is known as a severe psychiatric disorder with a broad range of clinical indications and symptoms such as positive and negative symptoms. This study was conducted with the aim of investigating the effect of melatonin on positive and negative symptoms of inpatients with schizophrenia. Method : This study was conducted as a randomized placebo-controlled trial (double-blind) in the population of patients with schizophrenia. Study samples were selected from inpatients with schizophrenia, according to the DSM-5 criteria, who had not been diagnosed with a depressive episode of schizophrenia based on the Calgary questionnaire and who also met the inclusion criteria. 46 patients with schizophrenia were randomly assigned to the intervention (6 mg melatonin per day as two 3 mg pills for six weeks) and placebo groups. The positive and negative symptom scale (PANSS) was used to assess the effect of treatment at T1 (before intervention), T2 (three weeks after beginning the intervention) and T3 (six weeks after beginning the intervention). To check the research hypotheses, multiple comparison statistics were used by the SPSS 22 software. Results: The placebo and melatonin groups had no significant difference in terms of PANSS scores (negative, positive, general and total symptom scores) at T1. Also, there was no difference in PANSS scores between the two groups at T2. However, at T3, there was a significant difference between the two groups only in the score of negative symptoms of PANSS (P = 0.036), so that negative symptoms of schizophrenia were significantly reduced in the intervention group compared to the placebo group. Furthermore, based on within-group analyzes, all PANSS scores were significantly reduced in the two groups at T2 and T3 (P < 0.05). Conclusion: Long-term use (at least six weeks) of melatonin can improve the negative symptoms of schizophrenia. Since antipsychotics can better affect the positive symptoms, the use of melatonin in combination with these drugs may perhaps further improve the patients’ symptoms.