We identified 11 structural MRI studies that examined adult chronic cannabis users and met our selection criteria (Table 1). Structural differences were obtained in seven of them in terms of global brain measures [143] or gray/white matter changes [144]–[149]. Four studies did not find any significant structural alterations when comparing chronic cannabis users with healthy controls [150]–[153]. The abstinence period for all participants before they underwent the structural MRI was between 12 and 24 hours, apart from two studies [145], [152] (for details see Table 1).
