The major objective of the study is to evaluate the tolerance of headache and safety in Taiwan Taiwanese patients who are receiving two different dosing regimens of Aggrenox and Aggrenox placebo. The first group will start with placebo on days 1-4, daily dose on days 5-14, and following by b.i.d treatment on 15-28 days. This group will also receive a matching placebo in the morning and one Aggrenox capsule in the evening before on days 5-14. It enables to reduce the perception of dipyridamole-associated headache. The second group will receive the placebo twice daily on days 1-4, and medication twice daily for the remaining course. The third group will receive the placebo twice daily for the whole course.