Psychology, 2010, 1, 233-237
doi:10.4236/psych.2010.14031 Published Online October 2010 (http://www.SciRP.org/journal/psych)
233
Association between Severity of Cannabis
Dependence and Depression
Karina Karolina Kedzior1,2*, Mathew Martin-Iverson1,2
1,2Clinical Neurophysiology Unit, Graylands Hospital, Mt Claremont, Australia; 1,2Pharmacology & Anaesthesiology Unit, School of
Medicine & Pharmacology, Faculty of Medicine, Dentistry & Health Sciences, University of Western Australia, Crawley, Australia.
Received May 19th, 2010; revised June 21st, 2010; accepted August 23rd, 2010.
ABSTRACT
Objective. The aim of the current study was to investigate the relationship between self-reported severity of cannabis
dependence and symptoms of depression. Method. The lifetime diagnoses of depression and cannabis misuse (abuse
and/or dependence) were obtained from 50 participants recruited from the general community, using a self-completed
diagnostic interview (CIDI-Auto 2.1). The lifetime severity of cannabis dependence was established using a standard
questionnaire, Severity of Dependence Scale (SDS). Results. Of the 19 participants with mental illness diagnoses, 14
(74%) reported depression symptoms. The 14 participants with depression diagnoses had significantly more cannabis
misuse diagnoses and significantly higher SDS scores compared to those without mental illness diagnoses (N = 31).
SDS scores significantly predicted presence or absence of CIDI depression diagnoses with a 69% overall rate of cor-
rect predictions. As SDS scores increased the odds of classification into depressed versus non-depressed groups was
1.3 (95% C.I. 1.02-1.57). Conclusion. The presence of lifetime depression symptoms is associated with higher lifetime
severity of cannabis dependence and more lifetime cannabis misuse symptoms in otherwise healthy research volunteers.
Keywords: Severity of Cannabis Dependence, Depression, CIDI-Auto 2.1, SDS
1. Introduction
People with psychotic illnesses have a higher rate of
regular cannabis use than those from the general popula-
tion [1]. Even though not receiving as much attention, the
link between cannabis use and affective disorders, such
as depression, also appears to exist [2]. In general, well-
designed, large epidemiological studies of the general
population in Australia and New Zealand suggest that
heavy cannabis use and depression co-occur at levels
significantly greater than chance [2].
While the severity of cannabis use is often measured in
terms of frequency of use, a more appropriate measure
might be dependence on cannabis. Specifically, the con-
struct of dependence combines an increased frequency of
substance use with psychological and physiological con-
sequences of such a use [3].
Therefore, the aim of the current study was to investi-
gate the association between severity of dependence on
cannabis and presence of depression symptoms in volun-
teers from the general population recruited for non-treat-
ment related research. Based on the epidemiological evi-
dence mentioned above, it was hypothesised that partici-
pants reporting depression symptoms would also report
greater severity of cannabis dependence. Furthermore, it
was hypothesised that absence or presence of depression
symptoms could be predicted using severity of cannabis
dependence.
2. Materials and Methods
2.1. Participants
This study was approved by the Human Research Ethics
Committees at the University of Western Australia and
the North Metropolitan Mental Health Service in Perth,
Australia. Following the informed consent, 50 volunteers
participated in the current study included in a larger pro-
ject investigating the effects of cannabis use on the startle
reflex [4]. The participants were recruited from the gen-
eral community of Perth using advertisements at Red
Cross blood donation clinics and at a major newspaper
(“The West Australian”). The participants were screened
for absence of major psychiatric illnesses except for de-
pression, neurological disorders, and substance use dis-
*Corresponding Author: Dr. Karina Kedzior De Santis, Jacobs Univer-
sity Bremen, School of Humanities and Social Sciences, Campus Ring
1, 28759 Bremen, Germany.

Association between Severity of Cannabis Dependence and Depression
234
orders other than cannabis misuse. Of the 50 participants,
28 reported using cannabis for at least 12 months pre-
ceding the testing session. The participants received AU
$20 for their participation in the project.
2.2. Procedure
All participants self-completed a Composite International
Diagnostic Interview, CIDI-Auto 2.1 [5], to establish
their lifetime presence of major psychiatric symptoms
and/or cannabis misuse symptoms (abuse and/or de-
pendence) according to the ICD-10 and/or DSM-IV di-
agnostic systems. Of the 50 participants 31 had no psy-
chiatric diagnoses (‘No diagnoses’ group) and 19 were
assigned psychiatric illness diagnoses. The participants
with diagnoses other than depression were excluded (N =
5; ICD-10 and/or DSM-IV delusional disorder N=3 and
brief psychotic disorder N = 2) such that the final ‘De-
pression diagnoses’ group consisted of 14 participants
with diagnoses ranging from dysthymia to severe depres-
sion according to DSM-IV and/or ICD-10 (refer to Table
1 for a full list of diagnoses).
All participants who had ever used cannabis completed
a self-reported questionnaire, Severity of Dependence
Scale, SDS [6], to establish their lifetime severity of can-
nabis dependence. The SDS is a five-item questionnaire
focusing on the psychological aspects of dependence,
such as control over cannabis use, anxiety about use, and
difficulty stopping [6]. The severity of dependence is
established by rating each answer on a scale from 0 to 3.
The range of possible scores on this questionnaire is be-
tween 0-15 indicating minimum to maximum severity of
cannabis dependence respectively. Participants who had
never used cannabis were automatically assigned a score
of zero indicating lack of cannabis dependence.
The self-reports regarding cannabis use were found to
be valid and consistent in the current sample of partici-
pants [7]. Similarly, both the CIDI-Auto 2.1 and SDS have
acceptable psychometric properties. Specifically, high
Cronbach’s alphas and intra-class correlation coefficients
indicate a good internal consistency and test- retest reli-
ability of SDS [6,8-10]. The validity of SDS is shown by
correlations between SDS scores and either behavioural
patterns of drug taking, such as dose, frequency and dura-
tion of use [6,7] or DSM-IV criteria for cannabis depend-
ence [8,10]. The test-retest and interrater reliability studies
of the CIDI show good to excellent kappa coefficients for
most diagnostic sections of the interview [11]. The CIDI
also has an acceptable validity [12]. For example, those
with cannabis misuse diagnoses (dependence and/or abuse)
on CIDI-Auto 2.1 have a significantly higher frequency of
use and significantly higher SDS scores than those without
such diagnoses [13].
2.3. Analysis
All statistical analyses were carried out using SPSS 17.0.
The various participant characteristics in the ‘No diag-
noses’ and ‘Depression diagnoses’ groups were com-
pared using independent samples t-tests ( p < 0.05) or
chi-square tests ( p < 0.05). A binary logistic regression
analysis was used to investigate if severity of cannabis
dependence can predict absence or presence of depres-
sion diagnoses on CIDI-Auto 2.1 in all 45 participants.
The model was computed using one dichotomous de-
pendent variable (absence = 0 or presence = 1 of depres-
sion diagnoses), one continuous predictor (SDS scores)
and a .5 cut-off for classification of participants into ei-
ther of the groups. The two assumptions relevant to a
one-predictor logistic regression model were met [14].
Specifically, the ratio of cases to predictors was above 10
(45 cases to one predictor) and the model goodness-of-fit
comparing the observed with predicted classification of
cases was assumed based on a non-significant Hosmer
and Lemeshow Test; χ2(4) = 3.3, p = 0.513.
3. Results
The results reported in Table 1 show that the ‘No diag-
noses’ and ‘Depression diagnoses’ groups were matched
on IQ, duration of formal education, male to female pro-
portion, and alcohol and nicotine use frequency over the
last 12 months since the testing session. However, the
participants with no diagnoses were significantly older
than those with depression diagnoses (Table 1).
The assessment of cannabis use characteristics has
shown that compared to the ‘No diagnoses’ group the
participants with lifetime CIDI diagnoses of depression
had significantly higher severity of cannabis dependence
(higher SDS scores) and a significantly higher proportion
of these participants had concurrent lifetime CIDI diag-
noses of cannabis misuse (abuse and/or dependence ac-
cording to ICD10 and/or DMS-IV; Table 1).
Furthermore, the binomial logistic regression model
was significant (χ2(1) = 5.1, p = 0.024). Specifically, the
higher SDS scores were able to significantly predict
presence of depression diagnoses (B = 0.2, Wald χ2(1) =
4.4, p = 0.036, odds ratio = 1.3, 95% confidence interval:
1.02-1.57). The odds ratio suggests that, as the predictor
(SDS score) increases by one unit, the odds of being
classified into the depression diagnoses group are 1.3
compared to the no diagnoses group. The overall rate of
correct classification was 69% and SDS was able to bet-
ter predict absence (87% correct predictions) than pres-
ence of depression diagnoses (29% correct predictions;
Table 2). Finally, only little variance in the dependent
variable was explained by the predictor according to Cox
and Snell’s R = 0.11 and Nagelkerke’s R = 0.15.

Association between Severity of Cannabis Dependence and Depression 235
Table 1. Characteristics of participants with and without diagnoses of depression on CIDI-Auto 2.1.
M ± SD (range)
No
diagnoses
N=31
Depression
diagnoses1
N=14
t or χ2 (df) Effect size2 ptwo-tailed
Age 34 ± 10 (18-56) 28 ± 9 (19-44) 2.0 (43) 0.29 0.048*
NART IQ 105 ± 7 (86-117) 105 ± 9 (90-117) 0.3 (43) 0.04 0.730
Education (years) 13 ± 2 (9-17) 13 ± 1 (10-15) 0.2 (43) 0.03 0.880
Male/Female 26/5 11/3 0.2 (1) 0.07 0.667
Alcoholic
drinks/week 6 ± 7 (0-28) 8 ± 9 (0-30) –0.4 (43) 0.06 0.678
Cigarettes/day 3 ± 7 (0-25) 4 ± 8 (0-30) –0.5 (43) 0.07 0.629
Cannabis use
details pone-tailed
SDS score 1 ± 2 (0-6) 4 ± 4 (0-13) –1.9 (16) 0.28 0.038*
Never/past/current
user3 9/7/15 4/1/9 1.8 (2) 0.20 0.208
None/sporadic/frequ
ent use4 16/3/12 5/1/8 1.3 (2) 0.17 0.257
Cannabis misuse5
(–/+) 22/9 5/9 5.0 (1) 0.33 0.012*
CIDI-Composite International Diagnostic Interview version Auto 2.1, NART- National Adult Reading Test, SDS- Severity of Dependence Scale. 1Depression:
ICD-10 dysthymia (N = 2), mild depression (N = 1), moderate depression (N = 3), severe depression (N = 4), and/or DSM-IV dysthymia (N = 1) and major
depression (N = 12). 2The effect size computation: r (possible range of values of –1 to 1) = √t2/(t2 + N1 + N2 – 2), where Ni is the sample size of each group; phi
(possible range of values of 0-1) = √χ2/N, where N is the total sample size. 3Past user = more than 12 months since the testing session, current user= within the
last 12 months of the testing session. 4Use within the last 12 months since the testing session (sporadic= monthly or less, frequent= at least weekly). 5Presence
(+) or absence (–) of lifetime cannabis misuse diagnoses (abuse and/or dependence on CIDI-Auto 2.1). *p < 0.05.
Table 2. Prediction of presence/absence of depression diagnoses on CIDI-Auto 2. 1 using c a nnabis de pe ndence (SDS) scores as
continuous predictor.
Predicted depression diagnoses
(% out of total N=45) % correct
Absent Present
Absent
N = 31
27 (60%)
True-negative
4 (9%)
False-positive
87%
(27/31)
Observed
depression
diagnoses Present
N = 14
10 (22%)
False-negative
4 (9%)
True-positive
29%
(4/14)
Overall % correct 69%
For abbreviations refer to Table 1.
3.1. Discussion
The results of this study indicate that higher severity of
cannabis dependence is associated with self-reported
symptoms of depression in participants recruited for
general research. However, the current participants were
mostly low-level users, at least over the last 12 months
since the testing session, compared to other studies
showing that depression is associated with heavy canna-
bis use [2]. Specifically, 25/45 (56%) of the current par-
ticipants reported either no use or monthly or less use
while the rest (20/45; 44%) were using cannabis at least
weekly over the last 12 months (Table 1). Furthermore,
most participants obtained low SDS scores indicating
that, in general, they had a low severity of cannabis de-
pendence. Therefore, it appears that not only severe but
even a low or moderate level of cannabis use is associ-
ated with symptoms of depression.
The results of the current study support the existence
of a link between cannabis use and depression symptoms.

Association between Severity of Cannabis Dependence and Depression
236
It can only be speculated that, similarly to the relation-
ship between cannabis use and psychotic illness, canna-
bis could either contribute to development of affective
mental illnesses or it could be used as self-medication
against existing symptoms of such illnesses. However,
the most likely scenario is that the relationship between
affective mental illness and cannabis use is due to other
common factors, such as a family history of depression,
similar age of onset of depression and cannabis use, or
common childhood stressors, including abuse, neglect or
unhealthy family dynamics. A common neurobiological
factor, such as changes in various neurotransmitter sys-
tems, including serotonin, noradrenaline, GABA, and
acetylcholine or CB1 receptors [15], may also link can-
nabis use with depression. The third-factor explanation is
supported by the evidence that the regular cannabis use
appears to explain only a small proportion of depression
in the population unlike the relationship between canna-
bis use and psychosis [2,16].
Even though the data in the current study were ob-
tained from self-reports these were found to be accurate
and consistent in the current participants. Specifically,
there was a high agreement between the self-reported
cannabis use and urine screens for cannabis over the last
24 h since the testing session [7]. There was also an ac-
ceptable consistency between multiple self-reports of
past cannabis use [7]. Furthermore, the current partici-
pants were also able to consistently report the symptoms
of cannabis misuse disorders (abuse and/or dependence)
on CIDI-Auto 2.1 [13]. In general, it appears that par-
ticipants in behavioural research unrelated to treatment,
such as participants in the current study, have very few
reasons for providing false reports about their substance
use and mental health particularly if they can remain
anonymous and are required to attend one testing session
only [7]. Therefore, even though it cannot be ruled out, it
is likely that the results of the current study were not sys-
tematically confounded by invalid and unreliable self-
reports.
Similarly to other studies [16], the relationship be-
tween cannabis use and depression can be considered
weak in the current study for a number of reasons. Firstly,
the small sample size could have accounted for a low
statistical power in the results which were marginally
significant and with low-medium effect sizes. Further-
more, the high variance in the data might have resulted
from the heterogeneity of the sample in terms of the
various types of depression diagnoses and the gender of
participants. Therefore, a larger, homogenous sample
should be used to assess the relationship between canna-
bis use and depression in males and females separately.
Secondly, the overall rate of correct predictions of de-
pression diagnoses using the severity of cannabis de-
pendence was low in logistic regression (69%) possibly
due to limitations of the two instruments used (SDS and
CIDI-Auto 2.1) and the low number of depression diag-
noses. Therefore, one way to improve this study would
be to utilise clinicians to confirm any psychiatric diag-
noses. Thirdly, it is also likely that the relationship be-
tween cannabis use and depression is more pronounced
in participants using cannabis more frequently than those
included in the current study. Therefore, a larger sample
of participants using cannabis with low- and high-fre-
quencies would help to investigate the role of heaviness
of use in the relationship between cannabis use and de-
pression. If replicated in larger samples, the finding that
even a low-frequency use of cannabis is associated with
depression could be useful for cannabis policy develop-
ment. Currently most cannabis policies are driven by
research showing the link between heavy cannabis use
and psychotic mental illness. However, it would also be
important to focus on a link between a low-level use and
depression because many users have limited access to
cannabis and use it irregularly.
In conclusion, the severity of cannabis dependence
appears to be associated with depression symptoms in
low-level cannabis users recruited from the general popu-
lation for non-treatment related research. More studies
are required to explain the directional meaning of such an
association and its neurobiological bases.
4. Acknowledgements
This research was funded by The Western Australian
Foundation for Research into Schizophrenic Disorders
and the NHMRC (grant no. 254619). The authors would
like to thank Ms. Andra Raisa Petca (B.A.) and Dr. Mi-
lan Dragovic for their assistance with preparation of this
manuscript.
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