Ticagrelor is a reversible and direct-acting oral antagonist of the P2Y12 (Purinergic receptor P2Y, G-protein coupled, 12) receptor for adenosine diphosphate, which provides faster, greater, and more consistent P2Y12 inhibition than Clopidogrel in patients with acute coronary syndrome, irrespective of the genetic variants affecting Clopidogrel metabolism. It is still undefined whether combination therapy of Ticagrelor and Aspirin is more effective than Clopidogrel and aspirin for minor stroke and transient ischemic attack (TIA). The primary purpose of the PRINCE trial is to evaluate the anti-platelet effects of a 3-month regimen of ticagrelor initiated with 180 mg loading dose followed by 90 mg twice/day combined with aspirin 100 mg/day during first 21 days versus a 3-month regimen of clopidogrel initiated with 300 mg loading dose of followed by 75 mg/day combined with aspirin 100 mg/day during first 21 days when initiated within 24 hours of symptom onset in high-risk transient ischemic attack or minor stroke.