The researchers also discovered a provocative and somewhat unexpected finding - that there were no net benefits associated with chronic caffeine administration. Consistent with this, volunteers reported increases in measures of 'tired,' 'fatigue,' 'sluggish' and 'weary.' Overall, these findings provide the most rigorous demonstration to date of physiological effects of caffeine withdrawal. Acute caffeine abstinence also produced changes in EEG (increased theta rhythm) that has previously been linked to the common withdrawal symptom of fatigue. More specifically, acute caffeine abstinence increased brain blood flow, an effect that may account for commonly reported withdrawal headaches. The team demonstrated that stopping daily caffeine consumption produces changes in cerebral blood flow velocity and quantitative EEG that are likely related to the classic caffeine withdrawal symptoms of headache, drowsiness and decreased alertness. Each participant's response to the caffeine or placebo was measured using three different measures - brain electrical activity via electroencephalogram (EEG) blood flow velocity in the brain via ultrasound and participants' self-reports of subjective effects via questionnaires. The group examined caffeine's effects in a double-blind study, which involved the administration of caffeine and placebo capsules.

They looked at brain electrical activity and blood flow during caffeine withdrawal to examine what was taking place physiologically during acute caffeine abstinence, including the likely mechanism underlying the common 'caffeine withdrawal headache.' Researchers from the University of Vermont College of Medicine and Johns Hopkins School of Medicine sought to investigate the biological mechanisms of caffeine withdrawal in a paper published recently in the online edition of the scientific journal Psychopharmacology.

Length of caffeine withdrawal symptoms