Effect of Melatonin on Schizophrenic Symptoms: a Randomized Placebo-Controlled Trial

Schizophrenia is a chronic psychiatric disorder characterized by a combination of positive symptoms (hallucinations, delusions, disorganized thinking) and negative symptoms (social withdrawal, reduced motivation, and blunted affect). While antipsychotic medications remain the primary treatment, they often fail to address negative symptoms, which are strongly associated with poor functional prognosis and reduced quality of life. Emerging evidence suggests that melatonin, a neurohormone primarily responsible for sleep regulation, possesses antioxidant and neuroprotective properties that may contribute to symptom improvement in schizophrenia.

This randomized, placebo-controlled trial aims to evaluate the efficacy of melatonin supplementation as an adjunct to standard antipsychotic therapy (risperidone 6-8 mg/day) in patients diagnosed with schizophrenia. The study will enroll 76 patients, randomly assigned to receive either melatonin (6 mg daily, administered as two 3 mg tablets before bedtime) or a placebo identical in shape, size, color, and taste for eight weeks. Participants will continue their standard antipsychotic regimen throughout the study period.

The primary outcome of the study is the change in Positive and Negative Syndrome Scale (PANSS) total score from baseline to week 8, assessing the overall impact of melatonin on symptom severity. The secondary outcomes include changes in PANSS negative symptom subscale scores, evaluating whether melatonin improves motivation, emotional expression, and social engagement.

To ensure methodological rigor, patients will be assessed at baseline and after eight weeks using the PANSS scoring system. Randomization will be performed using a lottery method, and the study will follow a double-blind design, ensuring that neither patients nor investigators are aware of the treatment allocation. Safety monitoring will include adverse event reporting, particularly evaluating the incidence of excessive sedation, dizziness, headache, and gastrointestinal disturbances.

This study aims to provide clinical evidence regarding the role of melatonin as an adjunctive treatment for schizophrenia. If proven effective, melatonin supplementation could offer a low-cost, well-tolerated intervention to enhance treatment outcomes in schizophrenia patients, particularly those experiencing persistent negative symptoms.

Inclusion criteria

• Patients aged between 18 to 50 years.
• Patients diagnosed with schizophrenia according to DSM-5 criteria, exhibiting both positive negative symptoms.
• Patients who score less than 6 on the Calgary Depression Scale for Schizophrenia (CDSS), indicating no significant depressive episode, will be considered eligible.

Exclusion criteria

• Patients with a known hypersensitivity or allergy to melatonin or any of its excipients.
• Patients with a current or past diagnosis of major depressive disorder, bipolar disorder, or obsessive-compulsive disorder, unless these are in full remission and do not require active pharmacological treatment.
• Patients with any unstable or serious medical condition (e.g., cardiovascular, hepatic, renal, or respiratory diseases) that could interfere with the study outcomes or pose additional risk to the patient.
• Married women of reproductive age, unless they use a reliable non-hormonal contraception method.
• Patients with neurological disorders, such as epilepsy, Parkinson's disease, or traumatic brain injury, which may mimic psychiatric symptoms.
• Use of antiepileptic, antihypertensive, anticoagulant, or anti-platelet drugs.
• Use of inhibitors or stimulants of hepatic isoenzymes that metabolize melatonin or olanzapine (e.g., omeprazole, rifampin, fluvoxamine, ciprofloxacin, carbamazepine, modafinil).
• History of addictive disorders.