Psychopharmacology (2003) 167:54–62 DOI 10.1007/s00213-002-1360-3 ORIGINAL INVESTIGATION Peter J. Rogers · James Martin · Chloe Smith · Susan V. Heatherley · Hendrik J. Smit Absence of reinforcing, mood and psychomotor performance effects of caffeine in habitual non-consumers of caffeine Received: 16 July 2002 / Accepted: 14 November 2002 / Published online: 25 February 2003  Springer-Verlag 2003 Abstract Rationale: The extent to which the measured (and felt) psychostimulant effects of caffeine represent a real benefit of caffeine consumption or merely withdrawal reversal is unclear. Results showing positive psychostim- ulant effects of acute caffeine administration in habitual non-consumers of caffeine would provide evidence for a net benefit of caffeine unconfounded by withdrawal. Objectives: To compare the mood, alerting, psychomotor and reinforcing effects of caffeine in caffeine non- consumers and acutely (overnight) withdrawn caffeine consumers. Methods: In experiment 1, these participants consumed two differently flavoured dinks, one containing 100 mg caffeine and the other containing no caffeine. Each drink was consumed on 4 separate days in semi- random order, and self-ratings of mood and alertness were completed before and after drink consumption. On day 9, both drinks contained 50 mg caffeine and drink prefer- ence (choice) and intake were assessed. In experiment 2, mood, alertness and performance on a long-duration simple reaction time task were assessed before and after administration of 100 mg or placebo in a single test session. Results: Prior to receiving caffeine, the (over- night withdrawn) caffeine consumers were less alert and more tense than the non-consumers. Caffeine only had significant reinforcing, mood and psychomotor perfor- mance effects in the caffeine consumers. The reinforcing effect of caffeine was evident from an effect on drink intake, but drink choice was unaffected. Caffeine in- creased self-rated alertness of both caffeine consumers and non-consumers; however, for some of the non- consumers this was associated with a worsening of performance. Conclusions: These results support the hypothesis that the psychostimulant and related effects of caffeine are due largely to withdrawal reversal. Keywords Caffeine · Caffeine withdrawal · Drug reinforcement · Psychostimulant · Mood · Alertness · Psychomotor performance Introduction An important question raised by recent research on the psychostimulant effects of caffeine concerns the extent to which these effects represent a net increase in alertness and improvement in mental performance and the extent to which they are due to withdrawal reversal (reviewed recently by James 1997; Rogers and Dernoncourt 1998; Rogers 2000). In its strongest form, the withdrawal reversal hypothesis states that there are no net benefits of caffeine consumption for mood, alertness, or mental performance: in real life, the regular caffeine consumer undergoes repeated cycles of caffeine consumption and withdrawal, and all that caffeine does is to reverse the negative effects of caffeine withdrawal. Consequently, after overnight caffeine abstinence, caffeine consumption at breakfast increases alertness, but only to the (baseline) level that would have been experienced if the individual had never previously consumed caffeine (Goldstein et al. 1969; Richardson et al. 1995). Furthermore, although only a small dose of caffeine is required to reverse withdrawal, larger doses or repeated consumption during the morning appear to have little or no additional effect (Lieberman et al. 1987; Robelin and Rogers 1998; Smit and Rogers 2000). A second part of the withdrawal reversal hypoth- esis states that the withdrawal relief provided by caffeine intake reinforces preferences for caffeine-containing drinks (Rogers and Richardson 1993; Rogers et al. 1995; see also Hughes et al. 1993; Schuh and Griffiths 1997). Two ways of testing these ideas are to compare the responses to caffeine of acutely (e.g. overnight) with- drawn caffeine consumers with the responses of either long-tern withdrawn caffeine consumers, or habitual non- consumers (never) consumers of caffeine (Goldstein et al. 1969; Bruce et al. 1991; Richardson et al. 1995; James P. J. Rogers ( ) ) · J. Martin · C. Smith · S. V. Heatherley · H. J. Smit Department of Experimental Psychology, University of Bristol, 8 Woodland Road, Bristol, BS8 1TN, UK e-mail: Peter.Rogers@bristol.ac.uk Fax: +44-117-9288588