Interaction between drug and placebo effects: a cross-over balanced placebo design trial

Table 2 Drug, placebo, placebo+interaction, and total effects on systolic blood pressure, energy, sleepiness, and nausea levels.

	Drug Effect	Placebo Effect	Placebo+ interaction Effect	Total Effect
Energy level (mm*hr)	20.8 [3.8 to 37.8] P = 0.02	16.6 [4.1 to 29.0] P = 0.01	8.4 [-4.2 to 21.0] P = 0.19	29.5 [11.9 to 47.1] P = 0.001
Sleepiness level (ratio)	0.49 [0.30 to 0.91] P = 0.005	0.58 [0.39 to 0.86] P = 0.007	0.69 [0.49 to 0.97] P = 0.03	0.37 [0.22 to 0.64] P < 0.0001
Nausea level (ratio)	1.59 [1.00 to 2.52] P = 0.05	1.43 [0.91 to 2.27] P = 0.12	1.04 [0.74 to 1.47] P = 0.82	1.46 [0.91 to 2.34] P = 0.12
Systolic blood pressure (mm Hg*hr)	28.4 [20.5 to 36.4] P < 0.0001	1.2 [-3.0 to 5.4] P = 0.57	-0.2 [-4.6 to 4.1] P = 0.91	29.9 [22.3 to 37.6] P < 0.0001

Data are adjusted point estimate [95% confidence interval]. Point estimate is the difference between means (systolic blood pressure and energy levels) or ratio of geometric means (sleepiness and nausea levels). Drug effect = "receiving caffeine described as placebo" mean - "receiving placebo described as placebo" mean or ratio of their geometric means. Placebo effect = "receiving placebo described as caffeine" mean - "receiving placebo described as placebo" mean or ratio of their geometric means. Placebo+interaction effect = "receiving caffeine described as caffeine" mean - "receiving caffeine described as placebo" mean or ratio of their geometric means. Total effect = "receiving caffeine described as caffeine" mean - "receiving placebo described as placebo" mean or ratio of their geometric means. Unadjusted mean(SE) of energy (mm*hr), sleepiness (mm*hr), nausea (mm*hr), and systolic blood pressure (mm Hg*hr) levels were respectively, 293.5(10.1), 70.3(8.5), 23.8(4.3), and 499(5.2) when caffeine was described as caffeine; 284.9(8.9), 83.5(8.7), 23.8(4.7), and 500(5.1) when caffeine was described as placebo; 275.2(9.2),114.8(10.5), 23.7(5.1), and 469(4.3) when placebo was described as placebo; and 291.8(6.6), 91.1(8.3), 24.1(3.7), and 471(4.7) when placebo was described as caffeine.

ISSN: 1745-6215