Positron emission tomography (PET) can visualize and quantify receptors and other targets in the living human brain, and recent progress in radioligand development has enabled measurement of cannabinoid type-1 (CB1 ) receptors. Cannabinoid CB1 receptors have been implicated in multiple human diseases, such as obesity, mood disorders, and addiction. First in vivo human studies have shown distinctive spatial and temporal alterations in cannabinoid CB1 receptor binding in addictive disorders.