Nicotine effects on human affective functions. A systematic review of the literature on a controversial issue

The observation that nicotine modulates negative affectivity and have a mood enhancing effect mainly derives from studies conducted in general/clinical nicotine deprived populations and have been explained by the so called deprivation-reversal hypothesis (i.e., nicotine modulates affect because it alleviates withdrawal symptoms). However, experimental studies suggest that nicotine might modulate different affective functions (e.g., aggressiveness, anxiety) and exert a direct modulating effect on human affectivity. The present paper is a systematic review of the literature aiming at verifying this second hypothesis. A computerized search was carried out (PubMed/Medline 1960-2012). Inclusion criteria were: 1. English language papers published in peer reviewed journals; 2. experimental/quasi experimental design studies; 3. no deprived adults; 4. inclusion of a control condition; 5. no additional Axis I or II psychiatric disorders. Twenty-one papers met our inclusion criteria. Nicotine showed to alleviate depression both in smokers and in non-smokers, especially if vulnerable to depression or depressed, and this effect seemed related to the activation of the dopaminergic brain rewarding system. No clear effects on anxiety were found. Nicotine, thus, seems to exert a direct modulating effect on human mood. Possible limitations of the reviewed studies and future research directions are proposed.