Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)

Graduate Group


First Advisor

Martha J. Farah


Does non-medical use of prescription stimulants improve healthy cognition? What distinguishes healthy users of ADHD medication from their peers? The present project examined stimulants’ cognitive enhancement effects and the psychological profile of non-medical stimulant users. Study 1, a double-blind, placebo-controlled experiment, found no enhancing effect of mixed amphetamine salts (Adderall) on healthy participants’ inhibitory control, working memory, episodic memory, convergent creativity, perceptual intelligence, and a standardized achievement test. No moderating effects of baseline performance or COMT genotype were detected. Despite the lack of enhancement observed for most measures and most participants, participants nevertheless believed their performance was more enhanced by the active capsule than by placebo. In Study 2, we conducted a meta-analysis to determine whether stimulants’ cognitive enhancement potential is truly non-existent or simply small. Based on 47 double-blind, placebo-controlled experiments, we found evidence for small effects of amphetamine and methylphenidate on inhibitory control, working memory and episodic memory. Given the absence of conclusive evidence for practically significant stimulant effects in healthy people, we conducted Study 3 to infer about the motives for use from users’ psychological profile. Non-medical stimulant use appeared more strongly related to individuals’ perceived attention functioning than to their objectively measured attentional performance. Users reported lower motivation during the laboratory attention test and described their everyday study habits as poorer than a control group with no history of stimulant use. Taken together, these data imply that enhancement users struggle with below-average functioning in one or several cognitive, affective and behavioral domains, possibly seeking stimulants to compensate for these problems.

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Psychology Commons