Niacin (vitamin B3) has been studied as a potential treatment for cluster headaches due to its vasodilatory properties, which can help improve cerebral blood flow and potentially interrupt the pathological vasoconstriction associated with these headaches. When administered in high doses, niacin acts as a potent vasodilator through its activation of nicotinic acid receptors, leading to peripheral and cerebral vessel dilation that may help reduce the frequency and intensity of cluster headache episodes.