Heavy cannabis use and depressive symptoms in three Aboriginal communities in Arnhem Land, Northern Territory

K S Kylie Lee, Alan R Clough, Muriel J Jaragba, Katherine M Conigrave and George C Patton
Med J Aust 2008; 188 (10): 605-608. || doi: 10.5694/j.1326-5377.2008.tb01803.x
Published online: 19 May 2008

Mental health problems appear to be common in Australia’s Indigenous population.1-3 Compared with their non-Indigenous counterparts, suicide rates among Indigenous people aged up to 24 years are five times higher for females and three times higher for males.2 High levels of violence, incarceration and physical illness may be contributors to poor mental health and suicide in Indigenous Australians.1,2,4 In 2002, nearly a quarter (24%) of Indigenous people aged 15 years or more reported being victims of actual or threatened violence in the previous 12 months.2 Moreover, marginalisation, loss of control and challenges to cultural continuity are also likely to play a role.5

Heavy substance misuse is a further potentially modifiable contributor to high levels of mental disorder in Indigenous populations.1,6 Indigenous people are 4–5 times more likely than other Australians to be hospitalised for mental or behavioural disorders as a result of psychoactive substance misuse.7 Despite growing links between cannabis and mental disorders, including psychotic illness8 and depression,9,10 its contribution to mental disorders in Indigenous people has, until now, been little studied.

A small proportion of the general Australian population uses cannabis regularly for extended periods.11 However, in the Arnhem Land Aboriginal communities that are the subject of this study, a high prevalence of cannabis use has persisted from 2001, with 61% of males and 58% of females aged 13–36 years in a random sample of 162 people reporting using cannabis at least weekly in 2005–2006.12 In comparison, of current Australian cannabis users, only 24% of males and 21% of females aged 14 years or older used cannabis weekly or more frequently.13 In this study we explored the association between depressive symptoms and heavy cannabis use among Aboriginal people in Arnhem Land.


We studied three Northern Territory Aboriginal communities and smaller single-family “outstation” settlements with a combined population of around 1700 in a location about 630 km east of Darwin. Although near a mining town with 1000 non-Indigenous residents, these Aboriginal people generally live within their traditional cultural paradigm with cultural concepts largely intact. A single Indigenous language is spoken across these communities. English is a second language and the people’s skills in English vary.

This study was part of the third wave of a 5-year longitudinal study outlined below.

The 106 participants in this study were aged 13–42 years, and represented 12% of the population in that age group in the three communities. The mean age of the 57 males was 27.0 years (SD, 7.5 years) and of the 49 females was 25.6 years (SD, 6.5 years). Characteristics of the study participants are shown in Box 1.

Ethical approval was granted by the Human Research Ethics Committees of Menzies School of Health Research, the NT Health Department and James Cook University.

Depressive symptoms

A modified Patient Health Questionnaire-9 (PHQ-9)15 was administered by the interviewer to assess depressive symptoms in the fortnight prior to the interview. Modifications for local use were made in consultation with local Aboriginal health and mental health workers. Original response categories (never, several days, more than half the days, nearly every day) were simplified (never, a little, a lot). Scores of zero, one or two were allocated to the amended response categories. Cronbach’s α coefficient was used to assess internal validity of the modified questionnaire (α, 0.73; 95% CI, 0.47–0.98). Particular efforts were made to clarify whether self-reported depressive symptoms occurred outside usual daily experience (eg, lethargy versus tiredness after physical exertion). In the original PHQ-9, raw scores of ≥ 10 (out of a possible 27) indicate moderate–severe depression.15 This equates to ≥ 6.6 (out of a possible 18) in the modified PHQ-9 we used. Accordingly, raw scores of ≥ 6 were used to indicate a moderate–severe threshold of depressive symptoms.


Baseline comparisons of the randomly selected and opportunistically recruited interview samples showed no differences in sex, age, or heavy cannabis use (each P > 0.1). A greater proportion of males were lost to follow-up interview in 2005–2006 than females (P = 0.02), but there were no differences in baseline prevalence of heavy cannabis use (P = 0.77) or age (P = 0.21).

Concurrent substance use was common among heavy cannabis users who reported moderate–severe depressive symptoms, with 100% smoking tobacco, 47% (8/17) current alcohol drinkers and 6% (1/17) sniffing petrol. Among respondents without moderate–severe symptoms, concurrent substance use was also common, with 88% (71/81) smoking tobacco and a third (33%, 27/81) drinking alcohol.

Cannabis and depression

Just under a quarter of the sample (24%, 25/106; 31% of females [15/49]; and 18% of males [10/57]) reported symptoms indicative of moderate–severe depression (raw score on the modified PHQ-9 of ≥ 6).

One in seven (15%, 8/54) of the never, former and lighter users reported moderate–severe symptoms, compared with one in three heavy users (33%, 17/52).

Box 2 shows that heavy cannabis users were nearly three times more likely to report moderate–severe depressive symptoms than the remainder of the sample (OR, 2.8; 95% CI, 1.1–7.2). The association was similar in females (OR, 4.9; 95% CI, 1.3–17.9) and males (OR, 4.2; 95% CI, 0.8–21.7). After controlling for potential confounders (age, sex, current alcohol and tobacco use, and lifetime petrol sniffing), the association strengthened (OR, 4.1; 95% CI, 1.3–13.4). No significant interactions were found with sex or other substance use.

Restricting the analysis to symptoms that are associated with depression, but unlikely to be associated with cannabis intoxication (ie, anhedonia, depression, worthlessness and suicidal ideation), mean total scores for heavy users were significantly higher than those of the never, former and lighter users (P = 0.02).


We found a strong association between heavy cannabis use and moderate–severe depressive symptoms in this Indigenous Arnhem Land community sample. Rates of depression were high, with nearly a third of females and one in six males reporting moderate–severe symptoms. There are no similar data published reporting the prevalence of depressive symptoms and their associations with cannabis use in any Indigenous sample worldwide. Consistent with studies in non-Indigenous populations, the association between cannabis and depressive symptoms was clearest in heavy cannabis users,16,17 and remained after controlling for potential confounders including other substance use.

Several limitations of this study should be noted. A combined sampling strategy was necessary in these remote Indigenous communities where populations are small and highly mobile. Although those interviewed comprised 12% of all males and females in the 13–42 years age group, only part of the sample was randomly selected with the remainder being opportunistically recruited. It is therefore possible that the presence of depressive symptoms may have influenced participant recruitment in some way. We adapted the PHQ-9 (a widely validated measure of depressive symptoms)15 with the assistance of local Aboriginal health and mental health workers to ensure the instrument’s suitability in the local context and across age groups. A specific validation study was not undertaken after modifications were made, although the internal consistency of the instrument suggests reliability. It nevertheless remains possible that the construct assessed does not fully correspond with the Western concept of depression, warranting further investigation.

We cannot exclude the influence of confounding factors not measured, such as stress, violence and trauma which are widespread in Australian Aboriginal populations.2,6 In a study context such as this, where research conducted across language and cultural barriers faces considerable challenges, lengthy interviews with detailed examination of concurrent mental disorders, physical health, trauma, health service contact and other factors that may impact on the severity of depressive symptoms were not possible. For most individuals, a 25-minute interview was the maximum feasible. Depression might theoretically cause the levels of cannabis use we found through a process of self-medication. However, to date there has been little support for a “self-medication” hypothesis.9,17,18

The possibility that heavy cannabis use caused the depressive symptoms observed deserves consideration. The relationship observed elsewhere between daily use of cannabis and a higher frequency of diagnoses of depression16,17 is consistent with this view, but longitudinal studies in Indigenous samples would be needed to test this further.

The damaging effects of alcohol on Australian Indigenous communities are well recognised, and have led to community-driven policies restricting supply.3 These policies have been successful in reducing some social and health burdens associated with alcohol misuse. The high prevalence of cannabis use and emerging evidence of an association with mental disorders suggests a need for clinical interventions and preventive programs aimed at cannabis misuse in Indigenous communities, along with continued support for measures to reduce supply.19,20

  • K S Kylie Lee1,2
  • Alan R Clough1,3
  • Muriel J Jaragba4
  • Katherine M Conigrave2,5
  • George C Patton6

  • 1 School of Public Health, Tropical Medicine and Rehabilitation Sciences, James Cook University, Cairns, QLD.
  • 2 Faculty of Medicine, University of Sydney, Sydney, NSW.
  • 3 School of Indigenous Australian Studies, James Cook University, Cairns, QLD.
  • 4 Top End Division of General Practice, Darwin, NT.
  • 5 Drug Health Service, Royal Prince Alfred Hospital, Sydney, NSW.
  • 6 Centre for Adolescent Health, Murdoch Children’s Research Institute, University of Melbourne, Melbourne, VIC.



We thank the communities, respondents, Indigenous researchers, linguists and service providers for their participation and support. The assistance of Jenni Langrell (Northern Territory Health Department), Mira Branezac (New South Wales Health, Drug and Alcohol Health Services Library), Caroline Wurramara, Rhoda Lalara, Elizabeth Caldwell, Chris White and Sibella Herbert is also appreciated. This research was funded by the National Health and Medical Research Council and the Alcohol Education and Rehabilitation Foundation. Kylie Lee was supported by a National Health and Medical Research Council Training Scholarship for Indigenous Australian Health Research.

Competing interests:

None identified.

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