Background:Many patients presenting with migraine also complain of constipation. The relationship between these two symptoms has not been explored yet in detail. This study, therefore, was carried out to investigate the effect of treatment of constipation with lactulose on the improvement of migraine headache in patients who referred to neurology clinics in Arak.Materials and Methods:A total of 50 patients with migraine were selected based on the Headache International Society (HIS) index and the Rome Foundation is an independent not for profit 501(c) 3 organization that provides support for activities designed to create scientific data and educational information to assist in the diagnosis and treatment of functional gastrointestinal disorders (FGIDs) (ROME III) scale so as to diagnose their migraine and constipation. The patients were randomly divided into an experimental group and a control group. A 15 cc daily of lactulose syrup was prescribed to the experimental group with the antimigraine drugs (10-mg nortriptyline and 10-mg propranonol daily). In contrast, only the standard treatment for migraine was prescribed for the control group. The severity of disability was assessed based on the severity of migraine-induced disability (MIDAS) questionnaire. Having collected the data, the data analysis was carried out using Statistical Package for the Social Sciences (SPSS) (IBM Corp. Released 2013. IBM SPSS Statistics for Windows, Version 21.0. Armonk, NY: IBM Corp.) statistical t-tests, and repeated measures test.Results:The results of the independent sample t-test showed no significant difference between the control and intervention group’s main variables of the research before the intervention (P < 0.05). On the contrary, the results of the repeated measures test indicated that the mean scores ‑of the severity of disability and the severity of migraine pain between the measurement times were significantly different for the intervention and control groups, in a way that after one and/or two months of using lactulose syrup, the severity of disability and pain in the intervention group was lower than those of the control group (P < 0.001).Conclusion:Short-term follow-up of this study showed that lactulose syrup could remove the constipation with no significant side effects––can be used as an adjunct for the treatment of patients with migraine. However, future studies suggested for long-term consequences of constipation control.