Phenytoin is an anticonvulsant sodium channel blocker that stabilizes neuronal membranes and reduces neuronal hyperexcitability by preventing repetitive neuronal firing. In cluster headache treatment, it modulates pain signal transmission and neurogenic inflammation, potentially reducing the frequency and intensity of headache episodes. Its mechanism involves blocking voltage-gated sodium channels and decreasing abnormal neuronal excitation in trigeminal and pain-processing neural pathways.