BACKGROUND: There is no definite recommendation for melatonin supplementation in episodic migraine. This study aimed to evaluate the effect of melatonin on reducing the frequency and severity of migraine attacks. METHODS: This randomized, double-blind clinical trial was conducted at Golestan Hospital of Ahvaz, Iran, in 2021. A total of 60 patients with episodic migraine were randomly assigned into 2 groups of receiving 3 mg melatonin (intervention group; n=30) or the same dose of placebo (control group; n=30) along with baseline therapy (propranolol 20 mg, BID) for two months. The attack frequency, attack duration, attack severity (based on VAS), the number of analgesic intakes, drug complications, Migraine Disability Assessment score (MIDAS), and Pittsburgh sleep quality index (PSQI) were evaluated at baseline and in the first, second, third, and fourth months of follow-up. The independent RESULTS: In both groups, the frequency, duration, and severity of attacks, taking analgesics, MIDAS, and PSQI scores during follow-up decreased significantly (P<0.001). After treatment, the mean frequency (P=0.032) and duration of attacks (P=0.001), taking analgesic (P<0.001), and MIDAS (P<0.001) and PSQI scores (P<0.001) in the melatonin group were lower than placebo. Only the attack severity was not significantly different between the two groups (P=0.126). Side effects were observed in two patients (6.7%) in the melatonin group and one patient (3.3%) in the placebo group (P>0.999). CONCLUSION: Our study shows that melatonin was more efficacious than the placebo in the reduction of frequency and duration of migraine attacks. It was equally safe as the placebo and might be effective in the preventive treatment of episodic migraine in adults.