Table 3.

Pre- and post-dose concentrations of caffeine and paraxanthine after a period of 12 h or 24 h abstinence from caffeine

		Pre- dose concentrationμg ml−1		Post- dose concentrationμg ml−1
Period of abstinence	Subject	Caffeine	Paraxanthine	Caffeine	Paraxanthine
24 h	1	0.27	0.22	2.74	0.67
	2	1.23	1.25	2.07	1.39
3	< 0.1	0.19	1.66	0.89
4	0.59	0.43	2.47	0.85
5	< 0.1	< 0.1	1.58	0.42
6	< 0.1	0.26	0.66	1.03
48 h	7	< 0.1	< 0.1	0.53	0.46
8	< 0.1	< 0.1	1.01	0.80
9	0.12	0.15	1.47	0.58
10	< 0.1	< 0.1	0.96	0.65
11	< 0.1	< 0.1	0.68	0.37
12	< 0.1	< 0.1	1.02	0.60