The human brain contains specialized neurons that respond to cannabinoids. A reduction in the number of working cannabinoid receptors has been linked to both marijuana and alcohol dependence. However, many patients with psychiatric disorders also smoke tobacco, and it is possible that cannabinoid receptors also play a role in nicotine addiction.

To investigate these links, Hirvonen and colleagues [...] assessing the activity of cannabinoid receptors in the brains of smokers and nonsmokers using PET scans.