direct and indirect consequences of continual exposure of the cardiopulmonary system, cerebrovascular system and/or brain parenchyma to the combustion products of cigarette smoke. However, the potential mechanisms contributing to the neurobiological abnormalities observed are derived from in vitro and animal studies. Consequently, it is unclear if these mechanisms are actually operational in humans. Furthermore, it is uncertain to what extent, if any, the reported neurocognitive and neurobiological abnormalities reported in smokers are influenced by premorbid or comorbid factors. Overall, the following methodological limitations are present in the reviewed literature:
