Background and Aims: Organophosphate compound poisoning (OPCP) is associated with high incidence of delirium. Melatonin has been tried in the treatment of delirium and has shown a beneficial effect in OPCP. This study was conducted to know the effect of melatonin on duration of delirium and recovery profile in OPCP patients. Methods: Double-blind randomised placebo control trial in which 56 patients of OPCP confirmed by history and syndrome of OPCP with low plasma pseudocholinesterase, aged >18 years and weighing between 50 and 100 kg, and Acute Physiology and Chronic Health Evaluation II score of <20 were studied. Group M (n = 26) received tablet melatonin 3 mg and Group C (n = 30) received placebo tablet at 9 PM, every night throughout the Intensive Care Unit (ICU) stay. Delirium was assessed using the Confusion Assessment Method for ICU, thrice a day. Sedation was provided with injection midazolam, fentanyl and lorazepam. Duration of mechanical ventilation, vital parameters, ICU stay, sedative and atropine requirement, were recorded. Results: The time taken to be delirium free was significantly lower in Group M (6 ± 2.92 days) compared to Group C (9.05 ± 2.75 days) (P = 0.001) and prevalence of delirium was significantly decreased in Group M compared to Group C from day 3 onwards. The requirement of midazolam (Group M - 2.98 ± 4.99 mg/day, Group C - 9.68 ± 9.17 mg/day, P < 0.001) and fentanyl (Group M - 94.09 ± 170.05 μg/day, Group C - 189.33 ± 156.38 μg/day, P = 0.03) decreased significantly in Group M. There was no significant difference in the average atropine consumption (P = 0.27), duration of mechanical ventilation (P = 0.26), ICU stay (P = 0.21) and the number of patients requiring mechanical ventilation (P = 0.50). Conclusion: Orally given melatonin in organophosphate compound poisoning patients reduces the duration of delirium and the requirement of sedation and analgesia.