RESEARCH ARTICLE
The Co-Use of Tobacco and Cannabis Among
Adolescents Over a 30-Year Period*
LAUREN WEBSTER,a MICHAEL CHAITON,b MARITT KIRST,c
ABSTRACT
BACKGROUND: This study explores the patterns of use and co-use of tobacco and cannabis among Ontario adolescents over 3
decades and if characteristics of co-users and single substance users have changed.
METHODS: Co-use trends for 1981-2011 were analyzed using the Centre for Addiction and Mental Health Ontario Student Drug
Use and Health Survey, which includes 38,331 students in grades 7, 9, and 11. A co-user was defined as someone reporting daily
tobacco and/or cannabis use in the past month. Trends over time (by gender and academic performance) were analyzed with
logistic regression.
RESULTS: The prevalence of tobacco-only use, cannabis-only use, and co-use fluctuated considerably. During 1981-1993, there
were more tobacco-only users than co-users and cannabis-only users; since 1993 the prevalence of tobacco use has decreased
dramatically. Co-use prevalence peaked at 12% (95% confidence interval: 9, 15) in 1999, when prevalence of overall use of both
substances was highest. In 2011, 92% of tobacco users also used cannabis, up from 16% in 1991.
CONCLUSIONS: In 2011 nearly all students who smoke tobacco daily also use cannabis. Non-regular use of either substance is
highest now compared with the past 3 decades. Contemporary tobacco and cannabis co-users are significantly different than
past users. Youth prevention programs should understand the changing context of cannabis and tobacco among youth.
Keywords: tobacco; cannabis; adolescence.
Citation: Webster L, Chaiton M, Kirst M. The co-use of tobacco and cannabis among adolescents over a 30-year period. J Sch
Health. 2014; 84: 151-159.
Received on April 2, 2012
Accepted on December 3, 2012
A
fter alcohol, tobacco and cannabis are the most
commonly used drugs by youth in Canada.1-4
The prevalence of use of tobacco and cannabis peaked
in the late 1970s, declined throughout the 1980s, and
then underwent a sharp increase to peak again in the
late 1990s.3,5
The correlation between tobacco and cannabis use
is well established. Numerous studies have found that
adolescents who smoke cigarettes are significantly
more likely to use cannabis than those who do not
smoke.6-10 Studies have also found that cannabis use
significantly increases the risk of tobacco use onset
and nicotine dependence in adolescents and young
adults.11-13 Adolescent smoking is associated with
numerous problem behaviors other than cannabis use,
including the use of other substances (alcohol, cocaine,
etc), risky sexual behaviors, attempting suicide, being
in a physical fight, and low academic performance.14-16
Previous research has shown that male adolescents are
more likely than females to use cannabis4,17-19 and to
engage in other problem behaviors.20-22
Less understood is why youth would use multiple
substances over using a single substance alone. Suris
et al17 conducted a study to characterize adolescent
cannabis users in Switzerland who had never smoked
cigarettes by comparing them with co-users of tobacco
and cannabis and to abstainers of both substances.
When compared to youth using both tobacco and
cannabis, the cannabis-only users appeared to exhibit
fewer problem behaviors. These findings suggest there
may be key differences between co-users and single
substance users; however, we did not find studies
examining the changes in characteristics of co-users
and single users of tobacco and cannabis over different
a Student, ([email protected]), Dalla Lana School of Public Health, c/o Ontario Tobacco Research Unit, T523, 33 Russell St, Toronto, ON M5S 2S1, Canada.
bAssistant Professor, ([email protected]), University of Toronto, T523, 33 Russell St, Toronto, ON M5S 2S1, Canada.
c Assistant Professor, ([email protected]), University of Toronto, 155 College Street, Toronto, ON M5T 3M7, Canada.
Address correspondence to: Michael Chaiton, Assistant Professor, ([email protected]), University of Toronto, T523, 33 Russell St, Toronto, ON M5S 2S1, Canada.
The Ontario Tobacco Research Unit receives funding from the Ontario Ministry of Health and Long Term Care.
*Indicates CHES continuing education hours are available. Also available at http://www.ashaweb.org/continuing_education.html
Journal of School Health
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© 2014, American School Health Association • 151
eras of use. Exploration of these differences can lead
to a greater understanding of the fundamental factors
associated with the co-occurrence of risky behaviors
among youth.
Previous conclusions characterizing co-users have
focused on small periods of time, but with dramatic
changes in use, there may be concurrent changes
in those characteristics. School health interventions
require an understanding of the consistent characteristics of co-use and need to stay updated on the changing
demographics and patterns over time. This study seeks
to explore the patterns of use and co-use of tobacco
and cannabis among adolescents over 3 decades, from
1981 to 2011, and to examine whether the characteristic differences between co-users and single substance
users have changed over this time period.
METHODS
Participants and Procedure
This study used data collected as part of the Centre
for Addiction and Mental Health Ontario Student
Drug Use and Health Survey (OSDUHS) from the
16 cross-sectional, population representative, surveys
administered between 1981 and 2011. More detailed
information on design can be accessed online at http://
www.camh.ca/en/research/news_and_publications/
ontario-student-drug-use-and-health-survey/Documents/2011%20OSDUHS%20Docs/2011OSDUHS_
Detailed_DrugUseReport_2.pdf.23 The OSDUHS is a
population survey of Ontario students in grades 7 to
12 (grades 7 to 13 until 2003) who are enrolled in
Ontario public and Catholic regular school systems.
This self-administered, anonymous survey is conducted every 2 years with the purpose of identifying
epidemiological trends in student drug use, mental
health, physical activity, and risk behavior, as well
as identifying risk and protective factors. All survey
cycles are based on a random probability design. From
1981 to 1997, single-stage selection of school boards
was used, stratified by grade and region of Ontario.
From 1999 to 2011, the study design involved 2-stage
selection for school and class, stratified by region
and school type. Response rates varied from 84% to
62%, with declining response rates over time. These
rates are consistent with increasing number of school
boards mandating active consent forms. The decline
in rates is consistent across survey research generally,
and current response rates are above average for
student surveys with active consent.24 Previous
analysis has shown that response rates at schools
are nondifferential with regard to high- and low-risk
students.23
Until 1999, OSDUHS interviewed students only in
grade 7, grade 9, grade 11, and grade 13 (Ontario
Academic Credit). In 1999, OSDUHS was expanded to
interview students in grade 7 through grade 12 or 13.
152
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March 2014, Vol. 84, No. 3 •
Grade 13 was eliminated from the Ontario curriculum
in 2003. To ensure consistency across the time period,
this study used data only from students in grade 7,
grade 9, and grade 11. The overall average age for
grade 7, grade 9, and grade 11 students was 11.9, 13.9,
and 15.9 years, respectively. The analytic sample was
restricted to students with valid responses on use of
tobacco, cannabis, and covariates. Data from the crosssectional surveys were pooled with a final total sample
of 38,331 students (Table 1).
Instruments
Lower academic performance, which has been
linked to increased risk of tobacco use, cannabis use,
and a variety of other risky behaviors,15,25 is used as an
indicator of problem behavior. Academic performance
was determined by asking: ‘‘Overall, what marks do
you usually get in school?’’ Possible responses were
‘‘A (80-100%),’’ ‘‘B (67-79%),’’ ‘‘C (60-66%),’’ ‘‘D
(50-59%),’’ or ‘‘Less than D (below 50%).’’ Academic
performance was classified into 2 groups: A students
(those reporting achieving A’s) and non-A students
(those reporting achieving B’s or below). Tobacco use
was assessed by asking: ‘‘In the last 12 months, how
often did you smoke cigarettes?’’ Regular tobacco use
was defined as reporting smoking 1 or more cigarettes
per day. Cannabis use was assessed by asking: ‘‘In
the past month, how often (if ever) did you use
cannabis?’’ Cannabis use was defined as reporting
using cannabis 1 or more times in the past month.
To maximize validity and cross-survey comparability,
survey items were developed from recommended
international guidelines and other reputable student
surveys such as National Institute on Drug Abuse’s
Monitoring the Future, which have been shown to
produce valid and reliable results.26
Regular tobacco-only and regular cannabis-only
users were defined as reporting either regular tobacco
use or regular cannabis use with no regular use of
the other substance. A co-user was defined as one
who reported both regular tobacco use and regular
cannabis. A non-user was defined as one who reported
either no use at all or no regular use of both tobacco
and cannabis. Information on grade and region of
Ontario was also collected from OSDUHS.
Data Analysis
The prevalence estimates of tobacco-only users,
cannabis-only users, co-users, and non-regular users
were assessed for each survey cycle. Prevalence
estimates of the user types were also assessed when
stratified by sex, academic performance (A student or
non-A student), and grade for each survey cycle.
For each survey cycle, we determined the percentage of co-users given the regular use of at least 1
© 2014, American School Health Association
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© 2014, American School Health Association • 153
(95% CI)
Total sample size
2647
Regular co-users
Total
13
(10, 15)
Sex
Male
47
(40, 53)
Female
53
(47, 60)
Grade
Grade 7
2
(1, 3)
Grade 9
44
(33, 54)
Grade 11
54
(43, 65)
Academic performance
A student
6
(3, 9)
Non-A student
94
(91, 97)
Regular tobacco-only users
Total
10
(8, 11)
Sex
Male
40
(31, 50)
Female
60
(50, 69)
Grade
Grade 7
9
(6, 12)
Grade 9
48
(38, 58)
Grade 11
43
(32, 54)
Academic performance
A student
12
(6, 19)
Non-A student
88
(81, 94)
Regular cannabis only users
Total
8
(6, 9)
Sex
Male
76
(69, 83)
Female
24
(17, 31)
Grade
Grade 7
4
(3, 6)
Grade 9
37
(28, 46)
Grade 11
59
(50, 68)
Academic performance
A student
9
(1, 17)
Non-A student
91
(83, 99)
Non-users
Total
70
(66, 73)
Sex
Male
52
(48, 57)
Female
48
(43, 52)
%
1981
(33, 46)
(54, 67)
(18, 26)
(30, 42)
(36, 48)
(5, 12)
(88, 95)
(4, 6)
(59, 75)
(25, 41)
(5, 8)
(36, 49)
(44, 58)
(6, 17)
(83, 94)
(72, 77)
(45, 52)
(48, 55)
39
61
22
36
42
8
92
5
67
33
6
42
51
11
89
75
49
51
(3, 9)
(91, 97)
6
94
(9, 12)
(7, 13)
(38, 51)
(38, 52)
10
45
45
10
(48, 65)
(35, 52)
(9, 12)
3528
(95% CI)
56
44
10
%
1983
51
49
78
15
85
6
31
63
71
29
6
6
94
18
40
42
40
60
7
4
96
9
33
57
50
50
9
%
(48, 54)
(46, 52)
(76, 81)
(10, 20)
(80, 90)
(5, 7)
(25, 37)
(56, 69)
(65, 78)
(22, 35)
(5, 7)
(2, 9)
(91, 98)
(14, 22)
(34, 47)
(35, 48)
(33, 47)
(53, 67)
(6, 8)
(2, 7)
(93, 98)
(7, 11)
(27, 40)
(50, 64)
(42, 58)
(42, 58)
(7, 10)
3074
(95% CI)
1985
48
52
82
12
88
7
40
53
71
29
3
9
91
20
34
46
41
59
9
8
92
8
26
65
58
42
6
%
(45, 52)
(48, 55)
(80, 84)
(5, 20)
(80, 95)
(5, 9)
(33, 48)
(45, 60)
(60, 82)
(18, 40)
(2, 4)
(6, 13)
(87, 94)
(15, 24)
(27, 41)
(40, 52)
(34, 48)
(52, 66)
(8, 10)
(4, 13)
(87, 96)
(5, 12)
(19, 34)
(57, 73)
(50, 66)
(34, 50)
(5, 7)
3267
(95% CI)
1987
49
51
84
13
87
8
35
57
67
33
2
11
89
11
50
40
47
53
9
7
93
5
41
54
44
56
5
%
(48, 51)
(49, 52)
(79, 88)
(5, 20)
(80, 95)
(2, 14)
(5, 66)
(26, 87)
(57, 77)
(23, 43)
(1, 3)
(4, 17)
(83, 96)
(3, 19)
(26, 74)
(13, 67)
(41, 53)
(47, 59)
(7, 11)
(3, 12)
(88, 97)
(0, 10)
(9, 73)
(20, 89)
(37, 51)
(49, 63)
(3, 7)
2910
(95% CI)
1989
53
47
84
6
94
4
22
74
58
42
2
9
91
11
39
51
50
50
10
5
95
5
32
64
63
37
5
%
(47, 58)
(42, 53)
(80, 88)
(0, 12)
(88, 100)
(1, 7)
(0, 48)
(47, 100)
(50, 66)
(34, 50)
(1, 3)
(5, 13)
(87, 95)
(3, 18)
(13, 64)
(24, 77)
(42, 58)
(42, 58)
(7, 12)
(1, 10)
(90, 99)
(2, 7)
(13, 51)
(43, 85)
(54, 71)
(29, 46)
(3, 7)
2858
(95% CI)
1991
49
51
80
8
92
10
21
70
72
28
2
6
94
13
37
50
38
62
11
4
96
4
32
64
61
39
6
%
(46, 52)
(48, 54)
(78, 83)
(0, 15)
(85, 100)
(6, 13)
(13, 28)
(62, 77)
(61, 83)
(17, 39)
(2, 3)
(2, 9)
(91, 98)
(10, 17)
(31, 43)
(44, 57)
(31, 45)
(55, 69)
(10, 13)
(0, 8)
(92, 100)
(3, 6)
(24, 40)
(56, 72)
(51, 70)
(30, 49)
(5, 7)
2515
(95% CI)
1993
48
52
74
18
82
4
31
66
58
42
6
6
94
15
41
44
44
56
8
5
95
5
32
64
54
46
11
%
(45, 51)
(49, 55)
(72, 77)
(9, 26)
(74, 91)
(3, 5)
(22, 39)
(57, 74)
(50, 66)
(34, 50)
(5, 8)
(3, 10)
(90, 97)
(10, 20)
(35, 47)
(38, 50)
(37, 52)
(48, 63)
(7, 9)
(2, 8)
(92, 98)
(1, 8)
(26, 37)
(58, 70)
(47, 62)
(38, 53)
(10, 13)
2729
(95% CI)
1995
Table 1. Prevalence of Tobacco Use (Daily), Past Month Cannabis Use, and Co-Use Among Students in Ontario 1981-2011 With Subgroup Prevalence by Gender, Grade, and
Academic Performance
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%
29
71
(20, 27)
(73, 80)
(95% CI)
1997
46
33
21
%
(21, 31)
(40, 55)
(20, 33)
(95% CI)
1981
Total sample size
3000
Regular co-users
Total
11
(10, 13)
Sex
Male
49
(41, 56)
Female
51
(44, 59)
Grade
Grade 7
6
(3, 9)
Grade 9
32
(25, 38)
Grade 11
62
(56, 69)
Academic performance
A student
13
(9, 16)
Non-A student
87
(84, 91)
Regular tobacco-only users
Total
9
(7, 10)
Sex
Male
42
(36, 48)
Female
58
(52, 64)
Grade
Grade 7
16
(13, 20)
Grade 9
31
(26, 37)
Grade 11
52
(47, 58)
Academic performance
A student
16
(11, 20)
Non-A student
84
(80, 89)
Regular cannabis-only users
Total
6
(5, 8)
Sex
Male
56
(48, 64)
Female
44
(36, 52)
Grade
Grade 7
26
Grade 9
47
Grade 11
26
Academic performance
A student
23
Non-A student
77
%
Table 1. Continued
(0, 3)
(29, 50)
(48, 70)
(10, 25)
(75, 90)
(8, 11)
(35, 58)
(42, 65)
(4, 16)
(25, 49)
(40, 66)
(13, 27)
(73, 87)
(6, 10)
(53, 73)
(27, 47)
17
83
10
47
53
10
37
53
20
80
8
63
37
(44, 62)
(38, 56)
53
47
2
39
59
(9, 15)
2208
(95% CI)
12
%
1999
(27, 32)
(68, 73)
(42, 51)
(29, 37)
(18, 24)
(95% CI)
1983
64
36
9
20
80
13
39
48
30
70
6
10
90
3
42
54
55
45
12
%
28
72
38
35
27
%
(49, 78)
(22, 51)
(7, 12)
(7, 32)
(68, 93)
(3, 23)
(17, 60)
(26, 70)
(13, 46)
(54, 87)
(4, 8)
(4, 16)
(84, 96)
(1, 6)
(27, 58)
(39, 70)
(43, 68)
(32, 57)
(9, 15)
902
(95% CI)
2001
(25, 31)
(69, 75)
(34, 41)
(31, 40)
(24, 31)
(95% CI)
1985
60
40
12
20
80
14
32
54
37
63
4
12
88
5
37
59
60
40
9
%
28
72
35
33
32
%
(51, 68)
(32, 49)
(10, 14)
(7, 32)
(68, 93)
(3, 24)
(19, 45)
(40, 68)
(21, 52)
(48, 79)
(3, 5)
(6, 18)
(82, 94)
(0, 10)
(26, 47)
(47, 70)
(49, 71)
(29, 51)
(7, 11)
1539
(95% CI)
2003
(25, 31)
(69, 75)
(32, 39)
(29, 37)
(28, 35)
(95% CI)
1987
54
46
17
12
88
0
29
71
62
38
2
10
90
4
32
64
45
55
6
%
30
70
36
37
27
%
(48, 61)
(39, 52)
(14, 19)
(0, 25)
(75, 100)
(0, 0)
(14, 43)
(57, 86)
(43, 80)
(20, 57)
(1, 3)
(5, 15)
(85, 95)
(2, 7)
(19, 44)
(52, 76)
(33, 58)
(42, 67)
(4, 7)
2092
(95% CI)
2005
(27, 34)
(66, 73)
(14, 57)
(17, 57)
(4, 50)
(95% CI)
1989
52
48
11
5
95
11
30
59
68
32
2
13
87
2
25
73
58
42
3
%
16
84
36
33
30
%
(44, 60)
(40, 56)
(9, 13)
(0, 12)
(88, 100)
(6, 17)
(16, 44)
(44, 73)
(50, 87)
(13, 50)
(1, 3)
(4, 21)
(79, 96)
(2, 3)
(14, 36)
(62, 83)
(44, 72)
(28, 56)
(2, 4)
1720
(95% CI)
2007
(10, 21)
(79, 90)
(17, 56)
(11, 55)
(10, 51)
(95% CI)
1991
57
43
10
8
92
11
38
51
56
44
1
12
88
4
35
62
47
53
4
%
18
82
34
36
30
%
(49, 66)
(34, 51)
(8, 12)
(0, 18)
(82, 100)
(7, 16)
(5, 71)
(20, 82)
(29, 82)
(18, 71)
(0, 1)
(1, 23)
(77, 99)
(0, 7)
(17, 52)
(44, 79)
(32, 63)
(37, 68)
(2, 5)
2313
(95% CI)
2009
(14, 22)
(78, 86)
(30, 37)
(32, 40)
(26, 35)
(95% CI)
1993
72
28
7
1
99
22
2
76
54
46
1
34
66
16
25
59
56
44
2
%
19
81
36
35
28
%
(59, 85)
(15, 41)
(5, 9)
(0, 3)
(97, 100)
(0, 70)
(0, 4)
(28, 100)
(0, 100)
(0, 100)
(0, 1)
(0, 69)
(31, 100)
(0, 48)
(0, 53)
(21, 97)
(13, 99)
(1, 87)
(1, 3)
1029
(95% CI)
2011
(17, 21)
(79, 83)
(33, 40)
(32, 38)
(25, 32)
(95% CI)
1995
(49, 63)
(37, 51)
56
44
(42, 50)
(50, 58)
46
54
(43, 51)
(49, 57)
47
53
(36, 47)
(53, 64)
41
59
40
60
(38, 54)
(46, 62)
(35, 44)
(56, 65)
(23, 54)
(24, 42)
(19, 37)
39
33
28
(29, 41)
(31, 40)
(25, 34)
35
35
30
(32, 41)
(32, 38)
(26, 31)
36
35
29
(35, 48)
(30, 39)
(20, 27)
42
35
24
35
35
30
(32, 47)
(24, 48)
(14, 35)
(30, 40)
(31, 39)
(27, 33)
(47, 56)
(44, 53)
52
48
(46, 52)
(48, 54)
49
51
(45, 54)
(46, 55)
49
51
(45, 58)
(42, 55)
51
49
47
53
(45, 54)
(46, 55)
(42, 51)
(49, 58)
(88, 92)
90
(83, 88)
85
(82, 86)
84
(72, 79)
76
75
(68, 77)
(72, 79)
(25, 66)
(34, 75)
46
54
(23, 38)
(62, 77)
30
70
(22, 38)
(62, 78)
30
70
(21, 32)
(68, 79)
26
74
31
69
(18, 45)
(55, 82)
(23, 38)
(62, 77)
(0, 1)
(3, 33)
(67, 97)
0
18
82
(1, 5)
(22, 37)
(60, 76)
3
29
68
(1, 4)
(30, 46)
(51, 67)
3
38
59
(3, 5)
(35, 45)
(51, 60)
4
40
56
6
37
56
(3, 10)
(33, 65)
(29, 60)
(3, 9)
(29, 46)
(48, 65)
(95% CI)
%
46
54
47
53
(39, 45)
(55, 61)
(43, 51)
(49, 57)
40
36
24
36
39
25
(35, 42)
(30, 38)
(24, 31)
(25, 47)
(29, 49)
(18, 32)
50
50
49
51
(44, 50)
(50, 56)
(46, 53)
(47, 54)
73
70
(72, 76)
(65, 75)
31
69
(21, 39)
(61, 79)
30
70
(19, 33)
(67, 81)
(1, 5)
(33, 49)
(47, 64)
6
38
57
(1, 11)
(26, 50)
(44, 69)
7
49
44
RESULTS
Grade
Grade 7
3
Grade 9
41
Grade 11
56
Academic performance
A student
26
Non-A student
74
Non-users
Total
74
Sex
Male
47
Female
53
Grade
Grade 7
38
Grade 9
34
Grade 11
27
Academic performance
A student
42
Non-A student
58
%
(95% CI)
%
(95% CI)
%
(95% CI)
(95% CI)
%
(95% CI)
%
(95% CI)
%
(95% CI)
%
2011
2009
2007
2005
2003
2001
1999
1997
Table 1. Continued
substance to examine the prevalence of co-use irrespective of overall changes in prevalence of use (ie,
the percentage of co-users among co-users plus single
substance-only users). This provided mutually exclusive proportions of (1) co-users among all regular
tobacco users and (2) co-users among all regular
cannabis users.
Then, to test change over time of co-use versus
single substance use, we pooled the data from each
cross-sectional survey, restricting to users of at least 1
of the 2 substances. Two series of logistic regressions
models were conducted: 1 series comparing co-users
to tobacco-only users and 1 series comparing co-users
to cannabis-only users. For each outcome, we assessed
the trend of change over time in the relationship
between co-use and 1 substance-only use, entering
into the model a survey cycle year variable along with
square and cubed year variables. We then performed
backward selection, removing the higher order term if
not statistically significant. To test whether the effect of
the covariates (sex, academic performance, and grade)
varied over time, the models included an interaction
term between the year of the survey and the square
and cube of the year variable if applicable and the sex
variable, the academic performance variable, or the
grade variable. Again, backward selection was used to
reduce the interaction terms.
All analyses were conducted using SAS statistical
software, Version 9.2 (SAS Institute Inc., Cary, NC),
using survey procedures to account for the complex
survey designs. Data were weighted to adjust for
participation rates and accurately represent the student
population of Ontario.23
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•
Table 1 presents the prevalence estimates of
tobacco-only users, cannabis-only users, and cousers from 1981 to 2011. Tobacco-only use among
adolescents peaked in 1993 at 11% (95% confidence
interval [CI]: 10%, 13%) and continually declined
until 2011, when the prevalence estimate reached
1% (95% CI: 0%, 1%). Cannabis-only use decreased
throughout the 1980s to reach a low of 2.0%
(95% CI: 1%, 3%) in 1991. Since then, cannabisonly use increased, surpassing tobacco-only use in
2001 and reaching 17.0% (95% CI: 14%, 19%) in
2005, before declining. After a decline throughout
the 1980s the prevalence of co-use increased and
peaked in 1999 at 12% (95% CI: 9%, 15%). Couse has since been decreasing with the most recent
2011 prevalence estimate at 2% (95% CI: 1%, 3%).
Non-use throughout the time period ranged between
70% (95% CI: 66%, 73%) in 1981 and 90% (95% CI:
88%, 92%) in 2011. Trends in prevalence appear in
Figure 1.
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•
© 2014, American School Health Association • 155
Figure 1. Prevalence of Tobacco-Only Users, Cannabis-Only
Users, and Co-Users Among Ontario Students, 1981-2011
18
Figure 2. Prevalence of Co-Use Among Ontario Student
Tobacco Users and Cannabis Users, 1981-2011
100
90
% of cannabis users
that also use tobacco
80
% of tobacco users
that also use cannabis
Tobacco-only user
16
Cannabis-only user
Co-user
14
12
70
10
60
50
8
40
6
30
4
20
2
10
Percent of Co-Use Among Users
To show co-use as a proportion of total users, we
examined the prevalence of tobacco use among all
students who reported cannabis use, and separately,
the prevalence of co-use among all tobacco users.
From 1983 to 1997, the prevalence of tobacco use
among all cannabis users was greater than prevalence
of cannabis use among all tobacco users, as seen in
Figure 2. Between 1999 and 2001, these prevalence
estimates crossed over. From 2001 to 2011, the use
of tobacco among all cannabis users declined sharply
to approximately 25%, whereas the use of cannabis
among all tobacco users increased to approximately
92%.
Co-Users Versus Tobacco-Only Users
The likelihood of being a co-user compared to
a tobacco-only user varied significantly by time.
The cubic term for the year trend was significant
(chi-square = 52.08; df = 1; p < .001) for co-use compared to tobacco-only use (chi-square = 90.38; df = 1;
p < .001), along with significant squared and linear
variables (chi-square = 118.98; df = 1; p < .001). The
cubic trend suggests that the relationship between couse and tobacco use changed, and there was then a
reversal of those changes.
The effect of sex and grade on the likelihood of couse versus tobacco-only use did not significantly vary
over time. Overall, students who were more likely
to co-use compared to tobacco-only were boys (chisquare = 74.21; df = 1; p = <.001), and were in lower
grades (chi-square = 232.32; df = 1; p < .001).
The effect of academic performance did vary
marginally statistically significantly over time with
the linear (chi-square = 4.66; df = 1; p = .030) and
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2009
2007
2005
2003
2001
1997
1999
1995
1993
1991
1987
1989
1983
1985
0
1981
2009
2011
2007
2005
2003
2001
1997
1999
1995
1993
1991
1987
1989
1983
1985
1981
0
quadratic trends (chi-square = 4.57; df = 1; p = .032).
Students with lower academic performance (nonA scores compared with A’s) were more likely to
be co-users than tobacco-only users, but this effect
decreased through the 1980s and then increased, as
the prevalence of being a co-user given using tobacco
increased.
Co-Users Versus Cannabis-Only Users
The relationship of co-use to cannabis-only smokers
differed over time compared to co-use to tobaccoonly users. The cubic term for year trend was not
significant (chi-square = 0.129; df = 1; p = .720) for couse compared to cannabis-only; however, removing
the cubic term resulted in a significant linear (chisquare = 57.08; df = 1; p < .001) and quadratic terms
(chi-square = 128.29; df = 1; p < .001). The quadratic
trend suggests a u-shaped trend in the likelihood of
being a co-user versus a cannabis-only user. This is
consistent with Figure 2 where the proportion of
cannabis users who used tobacco increased, peaked
in the early 1990s, and then declined.
Unlike co-use versus tobacco, the effect of academic
performance on the likelihood of co-use compared to
cannabis did not vary significantly over time. Students
with lower academic performance (non-A scores) were
more likely to be co-users than tobacco-only users.
However, the effects of sex and grade on the
likelihood of co-use versus tobacco-only use did
significantly vary over time. Boys were less likely to be
co-users than cannabis-only users in the 1980s but that
effect decreased linearly (chi-square = 19.96; df = 1;
p < .001). Similarly, the grade of a student influenced
the likelihood of co-use versus cannabis-only use. With
© 2014, American School Health Association
higher grades, students became increasingly more
likely to be cannabis-only than regular co-users (linear
trend: chi-square = 14.79; df = 2; p < .001).
DISCUSSION
In the early 1990s, based on this series of
population-representative surveys, the majority of
cannabis users were co-users of tobacco whereas the
proportion of tobacco users that also used cannabis
was at a low. Since then, there has been a steady
increase in the proportion of cannabis users among
tobacco users and a steady decline in the proportion
of tobacco users among cannabis users. These trends
have led to a reversal in the proportion of co-users
among tobacco and cannabis users, with the most
recent data from the 2011 survey cycle showing that
approximately 92% of past year tobacco users also use
cannabis and only 25% of past year cannabis users also
use tobacco. Importantly and encouragingly, non-use
of either substance is at a 30-year low.
Over time, this study has found dramatic shifts in
the patterns of use and non-use of these substances
among school-age youth. It is important for health
interventions to recognize the changes in the profiles
of these substances to avoid normalization of risky
behaviors and align material with student realities.
About 90% of students in Ontario in 2011 used neither
tobacco nor cannabis regularly; thus, more specifically
targeted programs may be more effective at reaching
youth most at risk.
The current findings from the OSDUHS data
highlight important differences between adolescents
who use both tobacco and cannabis and those who use
only 1 of these substances. Co-users, when compared
to both tobacco-only and cannabis-only users, are
more likely to display lower academic performance.
Among youth who report past-year tobacco use, males
are more likely to also report past-year cannabis
use. Conversely, among youth who report past-year
cannabis use, boys are less likely to also report
past-year tobacco use. These findings are consistent
with existing research. In a study using data from
the 2004 Canadian Tobacco Use Monitoring Survey,
Leatherdale et al7 found that among current smokers
in Canada aged 15 to 24 years, boys and young men
were more likely than their female counterparts to
report past-year cannabis use. Moreover, Suris et al17
found that adolescents in Switzerland who used only
cannabis were more likely to be male and have higher
grades than co-users of tobacco and cannabis.
This study demonstrated that the relationship
between sex and being either a co-user or cannabisonly user has decreased in strength over the past
3 decades in this data set. In terms of sex, past
research has found that boys are more likely to
engage in risky behaviors than girls.20-22 Furthermore,
Journal of School Health
•
cannabis-only use among adolescents has, over time,
become increasingly associated with higher academic
performance when compared to co-use, with lower
academic performance as an indicator of problem
behaviors. It appears that cannabis use may have
become less associated with other risky behaviors over
time, whereas tobacco may have developed a greater
association with other risky behaviors.
The latter is consistent with research by Camenga
et al27 that found that since the early 1990s, adolescent
tobacco users have become more likely to engage in
risky sexual- and alcohol-related behaviors. As stricter
tobacco access laws and smoking bans have been
introduced and as the prevalence of tobacco use among
youth has been declining, smoking may have become
a more socially deviant behavior.27,28 Conversely,
the prevalence of cannabis use among adolescents
has increased considerably since the early 1990s and
surpassed tobacco use,5 indicating that cannabis use
may be an increasingly normative behavior.29,30 This
suggests that tobacco use, not necessarily cannabis use,
is a marker of higher orientation to high-risk behavior.
Other research has shown that youth today perceive
cannabis use as a more normative behavior than youth
cohorts of the 1980s and 1990s, whereas tobacco use
may have become perceived as riskier behavior. Previous research has found that social norms around the
use of cannabis, such as perceived risk and disapproval,
are important determinants of actual cannabis use and
explain the historical changes in use better than individual lifestyle factors.29,30 This apparent shift in social
norms, indicated by changes over time in association with sex and academic performance, could lead
to the underestimation of potential health effects of
cannabis use, including cannabis dependence, respiratory illnesses, and psychotic symptoms and disorders.31
Qualitative studies from Scotland and Switzerland
addressing the co-use of tobacco and cannabis have
revealed that adolescents perceive cannabis as a natural and less harmful substance than tobacco, as well
as assign it a more positive functional value.32,33 It
has been suggested that although the illegal aspects of
cannabis are often disseminated to youth as a means
of preventing use of the substance, increased information on the possible harmful effects of cannabis is
required.33
Limitations
While the OSDUHS is generally representative of
adolescents in Ontario, it does not include some
subgroups, such as school dropouts and street youth,
where substance use may be significantly higher than
in the rest of the population. Despite efforts made
to ensure confidentiality, the self-reporting nature
of the survey signifies that there is potential for
underreporting of tobacco and cannabis use. The
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© 2014, American School Health Association • 157
cross-sectional design of the study does not allow for
the determination of temporality or causal inferences
in the associations between substance use and risk
factors, such as gender and academic performance.
Patterns of use of cigarettes and cannabis differ and
the definitions of use (daily for tobacco, past month
for cannabis) were meant to reflect current, regular
usage, but are not necessarily behaviorally equivalent.
Finally, OSDUHS does not ask about the common
practice of combining tobacco and cannabis,34,35 which
may have implications for the definitions of user types
in this study.
Conclusions
Tobacco use is the leading preventable cause of
death and disease in the Western world.36 These
results suggest that over the past 3 decades, co-use of
tobacco and cannabis among youth in Ontario shifted
from being more likely to occur among cannabis users
to being more likely to occur among tobacco users.
Nearly all regular adolescent tobacco users also use
cannabis, but only modest numbers of cannabis users
also use tobacco. This shift in use was accompanied
by changes in the characteristics of the users and
co-users. The changes in relationships between cousers and cannabis-only users and sex and academic
performance suggest that cannabis use may have
become increasingly normative behavior in recent
years, whereas smoking may be perceived as a more
risky behavior. This highlights the need to develop
and evaluate contextually appropriate interventions
programs that address multiple risk factors.
Many social-influence-based deterrents health
intervention programs at schools have found limited
success in randomized controlled studies.37 One program, the Waterloo Smoking Prevention Project 3,
found that overall the interventions were not effective in most schools; however, they had a significant
positive effect in high-risk schools, suggesting that
interventions should be targeted to be most effective.38
This suggests that this type of social programming is
most effective in groups where prevalence is relatively
high, addressing issues relevant to social context and
‘‘normal’’ use of these substances. The characteristics associated with use and co-use are not constant
over time. School programs must be adaptive and
responsive to the particular characteristics of their
populations.
IMPLICATIONS FOR SCHOOL HEALTH
The substantial number of youth who reported couse of these substances over the 30 years from 1981
to 2011 emphasizes the possible benefits of multisubstance prevention programs. The large proportion of
co-use among smokers in recent years highlights the
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March 2014, Vol. 84, No. 3 •
need for prevention programs that recognize tobacco
use as an indicator of other high-risk behaviors by
addressing multiple risk behaviors simultaneously. The
possible benefits of implementing more multisubstance
prevention programs are further emphasized by previous research that has found clustering of health risk
behaviors in youth, particularly the co-occurrence of
alcohol, tobacco, and/or cannabis use.1,6,25 Traditionally, prevention interventions in schools have focused
on tobacco use being a population-level issue—a
normative product with widespread use—whereas
cannabis interventions have been grouped with other,
less commonly used illicit drugs. Conversely, among
jurisdictions that have seen dramatic declines in youth
smoking, more intensive, focused, high-risk interventions may be more appropriate. Overall, the high rates
of non-use of either of these substances suggest careful
targeting to high-risk populations.
The illegal aspects of cannabis are often disseminated to youth as a means of preventing use of the
substance; instead, increased information on the possible harmful effects of cannabis may be more effective.
Future research should consider examining the benefits of cannabis use prevention programming that, like
tobacco prevention programming, places an emphasis
on the possible health risks involved in the use of the
substance.
Human Subjects Approval Statement
The survey was approved by research ethics boards
at the Centre for Addiction and Mental Health and
at York University. This study was submitted to the
research ethics board at the University of Toronto and
was deemed exempt.
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