Table 4.

Frequency of use for improving academic performance by substance.

Frequency of use (for any purpose)	Caffeine	Alcohol	Dietary supplements	Prescription stimulants	Other prescription substances	Other illicit substances
	% (95% CI)	% (95% CI)	% (95% CI)	% (95% CI)	% (95% CI)	% (95% CI)
At least once a day	32 (29, 36)	0 (0, 0)	15 (12, 18)	0 (0, 0)	1 (0, 1)	1 (0, 1)
Once a week	16 (13, 18)	1 (0, 1)	5 (4, 7)	0 (0, 0)	0 (0, 1)	1 (0, 2)
1–2 times a month	7 (5, 9)	1 (0, 2)	2 (0, 0)	0 (0, 1)	0 (0, 1)	1 (0, 1)
Less than once a month	6 (4, 7)	1 (0, 2)	1 (0, 2)	1 (0, 2)	1 (0, 1)	0 (0, 1)
Used, but not in last 6 months	10 (7, 12)	3 (2, 4)	9 (6, 11)	3 (1, 4)	1 (0, 1)	1 (0, 2)
Never used	30 (27, 34)	94 (92, 96)	68 (65, 72)	96 (95, 98)	97 (96, 98)	96 (95, 98)