Average bioequivalence has been criticized for not adequately addressing individual variations. Importance of subjects' blinding in bioequivalence studies has not been well studied. We explored the extent of intra-subject pharmacokinetic variability and effect of drug-ingestion unawareness in subjects taking single caffeine product. A single-dose randomized cross-over design was used to compare pharmacokinetics of 200 mg caffeine, described as caffeine (overt) or as placebo (covert). Maximum concentration (C), C first time (T), area-under-the-concentration-time-curve, to last measured concentration (AUC), extrapolated to infinity (AUC), or to T of overt caffeine (AUC), and C/AUC were calculated blindly using standard non-compartmental method. Percentages of individual covert/overt ratios that are outside the ±25% range were determined. Covert-vs-overt effect on caffeine pharmacokinetics was evaluated by 90% confidence interval (CI) and 80.00-125.00% bioequivalence range. 32 healthy subjects (6% females, mean (SD) age 33.3 (7.2) year) participated in the study (28 analysed). Out of the 28 individual covert/overt ratios, 23% were outside the ±25% range for AUC, 30% for AUC, 20% for AUC, 30% for C, and 43% for T. There was no significant covert-vs-overt difference in any of the pharmacokinetic parameters studied. Further, the 90% CIs for AUC, AUC, C, AUC, and C/AUC were all within the 80.00-125.00% bioequivalence range with mean absolute deviation of covert/overt ratios of 3.31%, 6.29%, 1.43%, 1.87%, and 5.19%, respectively. Large intra-subject variability in main caffeine pharmacokinetic parameters was noted when comparing an oral caffeine product to itself. Subjects' blinding may not be important in average bioequivalence studies.