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The present study investigated the dose-effect relationship of caffeine on mental performance using a caffeine-sensitive rapid information processing task (RIP) in a pre/post cross-over design. Twenty female nonsmoking regular coffee drinkers received 0, 1.5, 3 and 6 mg/kg caffeine in a balanced order and the measurements were extended to cardiovascular, EEG and mood parameters. Surprisingly, the dose-effect curves for the different parameters were rather heterogeneous. Whereas increasing effects with increasing caffeine doses were observed for alpha- and beta-EEG frequencies, anxiety, wakefulness, and some coffee ratings, negative dose-effect relationships were obtained for RIP processing rate and blood pressure. No apparent dose-effect relationships were seen for reaction time and motor activity. Thus, it was concluded that the dose-response relationships are rather shallow and heterogeneous and that the different parameters have different ranges in which they are sensitive to caffeine. The caffeine doses which might have beneficial behavioral effects are at the lower end of the tested dose range and comparable to those found in caffeine-containing beverages.

A significant problem in assessing the relative relevance of nicotine and tar yield for compensatory smoking after switching from high to low yield cigarettes is that nicotine and tar yield are highly intercorrelated across conventional cigarettes and that the tar/nicotine ratios vary only within a modest range. A better differentiation between the impacts of nicotine and tar yield was expected by comparing in a laboratory experiment a new low nicotine/medium tar cigarette ("Next") with conventional low nicotine/low tar (ultra-light) cigarettes and with medium nicotine/medium tar cigarettes with respect to nicotine absorption and physiological effects. Twelve females, habitually smoking medium type cigarettes (> or = 0.7 mg nicotine) participated in the study. Neither the number of cigarettes smoked under field conditions nor the puffing behavior during the laboratory experiment differed between the three types of cigarettes. In the laboratory, Next produced only very small increases in plasma nicotine and changes in cardiovascular or EEG measures, whereas the effects of the medium cigarettes were in the expected range and those of the ultra-light cigarettes about halfway in between. The nicotine absorption/nicotine yield and the CO absorption/CO yield ratios were similar for Next and the habitual cigarettes, but about twofold higher for the ultra-light cigarettes. This suggests that gustatory and olfactory sensations, which are supposed to be more dependent on tar than on nicotine yield, may play a greater role for the regulation of smoking behavior than hitherto believed.

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