A randomized controlled trial will be conducted. Patients with asymptomatic intracranial / carotid stenosis will be randomized into two arms (1:1): an intervention arm and a control arm. Patients in the intervention arm will be treated with standard medical treatment combined with Natto Products V, whereas Patient in the control arm will be treated with only standard medical treatment . And the impact of Natto Products V on improving cerebral blood flow and cognitive function in patients with asymptomatic intracranial / carotid stenosis will be assessed by neuropsychological scale and multimode magnetic resonance imaging.

Inclusion Criteria:

• Patients aged ≥ 40 years
• ≥ 50% stenosis in unilateral intracranial / carotid artery
• Written informed consent available

Exclusion Criteria:

• Previous history of major head trauma and any intracranial surgery
• Intracranial abnormalities, such as intracerebral hemorrhage, subarachnoid hemorrhage and other space occupying lesions
• Extrapyramidal symptoms or mental illness which may affect neuropsychological measurement
• severe loss of vision, hearing, or communicative ability
• plan to be treated with surgery