Table 2.

Subjective aversive and reinforcing effects in twins receiving saline placebo before alfentanil

Variables (VAS)		Median effect (IQR)		Incidence (%)
		Saline	Alfentanil	Saline	Alfentanil
Sedation		0 (0–15)	75 (60–87)	48	100
Dizziness	- average	0 (0–0)	15 (0–40)	8	67
	- maximum	0 (0–0)	30 (0–70)	8	68
Nausea	- average	0 (0–0)	1 (0–32)	3	50
	- maximum	0 (0–0)	8 (0–70)	3	50
Pruritus	- average	0 (0–0)	20 (0–45)	15	71
	- maximum	0 (0–0)	35 (0–65)	18	72
Liking	- average	0 (0–0)	50 (0–75)	12	67
	- maximum	0 (0–0)	75 (40–90)	12	80
Disliking	- maximum	0 (0–0)	23 (0–70)	5	65

IQR = inter-quartile range, VAS = visual analogue scale