Not to all people,,,however, nitroglycerin, causes a notorious dilatation of the intracranial veins, and in persons prone to headaches and migraine, it may trigger a very trublesome hedache bordering with migraine...the reason is: All veins inside of the cranium have nervous terminals surrounding them , innervated by beta sympathetic fibers, sensitive to pain....when a vein dilates a bit too much, the distension of the vessel causes pain, quite exactly in the same manner, that our big bowel gives us pain or colics when is too distended... If nitroglycerin causes too much headache, its time to change it for another cardio protective vasodilator, for instance, nifedipine slow release.....or amliodipine 5 mg BD.... Its a matter of personal sensitivity to a particular medication...