Conditional probabilities of substance use

Among students who have used cigarettes at least once, 93 % have also used alcohol, 32 % cannabis, 12 % inhalants, 10 % tranquillisers or sedatives and 8 % NPS Table 10. Almost every student (87 % or more) that has used a licit or illicit substance also reported having used alcohol, but not every student who has tried alcohol has also tried another substance. Among students that have used alcohol, 54 % have also used cigarettes, 19 % cannabis, 9 % inhalants, 7 % tranquillisers or sedatives and 5 % or less NPS or other illicit drugs.

Of the students that have used cannabis, 91 % have also used cigarettes and 96 % alcohol, inhalants (18 %), NPS (20 %) or tranquillisers or sedatives (16 %). Approximately one in ten or fewer of these students (4-11 %) reported having used each of the other illicit substances included in the questionnaire in addition to cannabis. Among users of ecstasy, amphetamine, methamphetamine, cocaine, crack, LSD or other hallucinogens, heroin or GHB, 80 % or more have also used cigarettes and 73 % or more have tried cannabis. With respect to users of one of the drugs other than cannabis, the lowest probability of using one of the other drugs was 25 % of ecstasy users who said they had also used GHB. The highest probability was seen with respect to LSD use by students who had used GHB (71 %).

Finally, among the students that have used substances from the two groups, inhalants and tranquillisers or sedatives, about a quarter have used substances from both of the groups. Among the users of both groups of substances, 70 % stated they have also used cigarettes. Of the students that have used painkillers for getting high, almost half reported the use of tranquillisers or sedatives (46 %). Among students reporting use of NPS, a quarter have also used inhalants (26 %) or tranquillisers or sedatives (25 %) and 74 % have used cannabis. Use of illicit substances among the small group of students that have used anabolic steroids ranged from 35 % (crack) to 60 % (cannabis).

Table 10. Prevalence of lifetime use of substance B conditional on the lifetime use of substance A (percentage) and number of users of substance A (n)

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Substance A	n	Lifetime prevalence	Substance B
Substance A	n	Lifetime prevalence	Cigarettes	Alcohol	Cannabis	Ecstasy	Amphetamine	Methamphetamine	Cocaine	Crack	LSD/other hallucinogens	Heroin	GHB	Inhalants	NPS	Tranquillisers / sedatives	Painkillers	Anabolic steroids
Cigarette	39914	46	.	93	32	4	4	2	4	2	4	2	2	12	8	10	6	2
Alcohol	69189	79	54	.	19	3	2	2	3	1	2	1	1	9	5	7	4	1
Cannabis	13988	16	91	96	.	11	9	7	11	6	11	6	4	18	20	16	10	5
Ecstasy	2013	2	84	92	77	.	47	36	46	29	44	29	25	38	40	40	33	22
Amphetamine	1693	2	86	92	77	56	.	45	51	33	46	33	28	44	42	46	39	27
Methamphetamine	1162	1	85	92	79	62	66	.	60	47	55	44	36	50	46	49	46	35
Cocaine	1959	2	85	91	79	48	44	36	.	34	43	37	26	44	39	39	35	24
Crack	1074	1	83	89	79	55	52	51	62	.	51	47	38	55	43	45	45	36
LSD/other hallucinogens	1843	2	87	93	80	48	42	34	45	30	.	36	30	44	44	48	41	30
Heroin	1068	1	81	87	75	55	52	48	68	47	62	.	49	55	47	56	53	47
GHB	788	1	80	87	73	63	60	53	63	52	71	66	.	57	48	58	61	60
Inhalants	6507	7	71	93	38	12	11	9	13	9	13	9	7	.	15	23	18	8
NPS	3723	4	83	92	74	22	19	14	20	13	22	14	10	26	.	25	20	11
Tranquillisers/sedatives	5605	6	70	90	39	14	14	10	13	9	16	11	8	27	17	.	25	10
Painkillers	3024	4	75	91	47	22	22	18	23	16	25	19	16	39	25	46	.	17
Anabolic steroids	1094	1	77	90	60	41	41	37	44	35	50	46	43	48	36	49	48	.