Migraine is a common, heterogeneous neurological disorder affecting approximately 10-15% of the global population and is the third most prevalent disease worldwide. A wide range of pharmacological agents is available for migraine prophylaxis, with treatment selection generally guided by the patient's clinical profile, associated comorbidities, and individual tolerability. However, the effectiveness of preventive medications is often limited by adverse effects, leading to poor treatment adherence and discontinuation. Consequently, non-pharmacological interventions, particularly neuromodulation techniques, have gained increasing attention as potential therapeutic options for chronic migraine.

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique that has demonstrated efficacy in modulating refractory pain in patients with chronic migraine, fibromyalgia, spinal cord injury, and trigeminal neuralgia. In addition, it has shown therapeutic benefits in several neurological and psychiatric disorders, including depression, stroke, epilepsy, and Parkinson's disease. The present study aims to evaluate the efficacy of anodal tDCS applied over the primary motor cortex as an adjunctive therapy for reducing headache frequency in patients with chronic migraine.

A total of 32 participants with chronic migraine will be enrolled and randomized using block randomization with a block size of four, stratified according to the presence or absence of medication-overuse headache (MOH), through an online randomization generator. Participants will be allocated to receive either active or sham tDCS. Before randomization, all eligible patients will maintain a baseline headache diary for four weeks while continuing their existing prophylactic medications. Thereafter, they will undergo three 20-minute stimulation sessions administered during weeks 1, 5, and 9. Treatment outcomes will be evaluated at weeks 5, 9, and 12 using headache diary records and predefined objective assessment tools.