Causes of slowed blood flow in the basilar artery include atherosclerosis, vasospasm, and abnormal blood flow. 1. Atherosclerosis: Age factors, diabetes, and high blood pressure are high risk factors for atherosclerosis in the basilar artery of the brain. Atherosclerosis leads to narrowing of the lumen of the blood vessel, which may cause slowing of blood flow in the basilar artery. 2. Cerebral vascular spasm: exertion, emotional stress and other causes may lead to cerebral vascular spasm, which may cause the basilar artery blood flow to slow down. 3. Abnormal blood flow: Hyperlipidemia, severe dehydration, etc. may cause abnormal blood flow, which may lead to the slowing down of blood flow in the basilar artery. There may be other causes of basilar artery blood flow slowdown, which should be treated after combining the patient’s clinical symptoms and auxiliary examinations to clarify the cause.