9, p < .05; see Figure 1 for number of items consumed). kinase inhibitor Tipifarnib Participant-Rated Drug Effect Questionnaires No significant differences were observed on any participant-rated drug effect questionnaires, with the exception that the intermediate dose of methylphenidate produced a small increase relative to placebo (i.e., an increase of 0.36 on a 0 to 4 scale) on participant ratings of Performance Improved on the Drug Effect Questionnaire (absolute t10 value = 2.4, p < .05; data not shown). Cardiovascular Measures No significant differences were observed on heart rate, systolic pressure, or diastolic pressure. Discussion The finding that methylphenidate increased a number of smoking-related outcomes in the present experiment is concordant with results of previously published research (Cousins et al.

, 2001; Henningfield & Griffiths, 1981; Rush et al., 2005; Schuster et al., 1979; Sigmon et al., 2003; Stoops et al., 2008; Tidey et al., 2000; Vansickel et al., 2007, 2009). Importantly, the results of the present experiment indicate that methylphenidate increased choice of cigarettes relative to money, which extends previous findings with D-amphetamine (Sigmon et al., 2003; Tidey et al., 2000). In the more recent study, D-amphetamine increased cigarette-maintained responding on a progressive-ratio schedule in a subset of individuals while not altering responding for money, also available on a progressive-ratio schedule albeit during separate sessions (Sigmon et al., 2003). In the earlier study, D-amphetamine increased choices for cigarettes in a cigarette versus money choice task very similar to the one described here (Tidey et al.

, 2000). Taken together, these data suggest that stimulant-induced increases in cigarette smoking are likely due to stimulants enhancing the reinforcing efficacy of cigarettes over money. This effect is probably mediated by the increase in synaptic dopamine levels produced by stimulant drugs, given that nondopaminergic drugs do not increase smoking (Stoops et al., 2008; Vansickel et al., 2007). Overall, increased smoking following stimulant administration is most likely driven by interactions of behavioral and pharmacological factors (i.e., smokers engage in increased drug-taking behavior due to increased synaptic dopamine levels following stimulant administration).

The results also indicate that methylphenidate decreased caloric intake during sessions, which is concordant with previous findings from our laboratory (Rush et al., 2005; Stoops Cilengitide et al., 2008; Vansickel et al., 2007, 2009). While subjects were not required to choose between food and money (i.e., the reinforcing effects of food were not being tested), these results further support the notion that methylphenidate-induced increases in intake appear specific to cigarette smoking and are not due to an increase in overall behavior or activity.