Effects of caffeine on performance and mood: withdrawal reversal is the most plausible explanation.
BACKGROUND
Although it is widely believed that caffeine can enhance human performance and mood, the validity of this belief has been questioned, giving rise to debate. The central question is whether superior performance and mood after caffeine represent net benefits, or whether differences between caffeine and control conditions are due to reversal of adverse withdrawal effects.


OBJECTIVE
To provide a focussed review of relevant experimental studies with the aim of clarifying current understanding regarding the effects of caffeine on human performance and mood.


METHODS
To avoid the shortcomings of standard placebo-controlled studies, which are ambiguous due to failure to control for the confounding influence of withdrawal reversal, three main experimental approaches have been employed: studies that compare consumers and low/non-consumers, pre-treatment and ad lib consumption studies, and long-term withdrawal studies.


RESULTS
Of the three approaches, only long-term withdrawal studies are capable of unambiguously revealing the net effects of caffeine. Overall, there is little evidence of caffeine having beneficial effects on performance or mood under conditions of long-term caffeine use vs abstinence. Although modest acute effects may occur following initial use, tolerance to these effects appears to develop in the context of habitual use of the drug.


CONCLUSIONS
Appropriately controlled studies show that the effects of caffeine on performance and mood, widely perceived to be net beneficial psychostimulant effects, are almost wholly attributable to reversal of adverse withdrawal effects associated with short periods of abstinence from the drug.
James
Jack E
JE
Department of Psychology, National University of Ireland, Galway, Ireland. j.james@nuigalway.ie
Rogers
Peter J
PJ
D000339:Affect / Q000187:drug effects*; D001143:Arousal / Q000187:drug effects*; D001288:Attention / Q000187:drug effects*; D002110:Caffeine / Q000009:adverse effects* / Q000494:pharmacology; D000697:Central Nervous System Stimulants / Q000009:adverse effects* / Q000494:pharmacology; D004361:Drug Tolerance; D005500:Follow-Up Studies; D006801:Humans; D012892:Sleep Deprivation / Q000523:psychology; D013375:Substance Withdrawal Syndrome / Q000523:psychology*
D000697:Central Nervous System Stimulants; D002110:Caffeine