['Individuals who quit smoking frequently experience symptoms of anxiety and/or depression. It is not clear whether these symptoms index liability to negative affect generally or whether such symptoms are a function of nicotine withdrawal and are thus indexed by nicotine dependence (ND).', 'A population-based sample of twins (N = 4,777 individuals) reported their lifetime history of psychopathology, ND, and symptoms of anxiety and depression experienced after attempts to quit smoking. Co-twin phenotype was used to predict withdrawal-induced symptoms of negative affect and to test whether genetic factors influence liability to these symptoms.', "Co-twin's ND was significantly associated with nicotine withdrawal-induced symptoms of anxiety and depression. Furthermore, monozygotic co-twins more strongly predicted outcome than did dizygotic co-twins, indicating that genetic factors contribute to risk. Co-twins' history of psychopathology did not predict outcome, suggesting that liability to withdrawal-induced negative affect is independent of a liability to negative affect outside the context of nicotine withdrawal."] Is nicotine withdrawal-induced negative affect a function of nicotine dependence and not liability to depression or anxiety?