FIG. 4. Effects of double-blind substitution of placebo capsules for caffeine capsules (100 mg/day) on mean ratings of headache and energy/active in four withdrawal-sensitive subjects. Shaded areas show the range of means from the initial 6-day caffeine period. Asterisks indicate which placebo days are significantly different from the initial caffeine period (p {ewc MVIMG, MVIMAGE,!lesseq.bmp} 0.05). (Redrawn from ref. 54.)