Vertebrobasilar dissecting aneurysms (VBDAs) are one of the most important causes of stroke in young and middle-aged people, and the natural history of VBDAs is complex and varied, often leading to high rates of disability and mortality. For some patients with VBDAs who are not suitable for surgical entrapment and intervention, pharmacologic therapy may be used to slow the progression of VBDAs. Metformin (MET) has been shown to act as an anti-inflammatory, anti-oxidative stress and improve vascular endothelial function by inhibiting smooth muscle cell phenotypic transformation, proliferation, migration and apoptosis, thereby reducing the incidence of intracranial aneurysms and rupture rates, and MET may be a suitable candidate. Inflammatory response plays an important role in the occurrence, development and rupture of VBDAs. Inflammatory response in the aneurysm wall can cause endothelial and smooth muscle cell injury and apoptosis, leading to degenerative changes in the vessel wall and increasing the risk of rupture of VBDAs. High-resolution magnetic resonance vessel wall imaging (HR-VWI), which can clearly show the structure of the vessel wall and reflect the active degree of inflammatory reaction in the aneurysm wall, has been widely used in the assessment of intracranial aneurysm instability. In this study, we propose to conduct a multicenter, prospective, randomized study to investigate whether MET reduces the degree of aneurysm wall inflammatory response in VBDAs by performing HR-VWI scans in patients with VBDAs and obtaining quantitative parameters reflecting the inflammatory response of the aneurysm wall.