Home > Cannabis use: understanding other illicit drug use, drug-related morbidity and dependence.

Rabiee, Rynaz (2022) Cannabis use: understanding other illicit drug use, drug-related morbidity and dependence. PhD thesis, Karolinska Institutet.

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External website: https://openarchive.ki.se/xmlui/handle/10616/47961

Approximately 200 million people worldwide use cannabis, which is a psychoactive substance that affects the brain function, human behavior, and consciousness. Yet, our current state of knowledge about cannabis use in relation to mental health is quite inconclusive. While some associations are well-established; for instance, that cannabis use increases the risk of schizophrenia and other psychotic disorders, other relationships remain to be elucidated. Increased understanding of cannabis use and related health effects is of the utmost importance, in order to facilitate informed decisions with regards to both public health interventions and healthcare. This thesis aimed at increasing the understanding of cannabis use, other illicit drug use, and drug-related morbidity.

In the first study, we used survey data from a longitudinal population-based cohort in Stockholm Region, with linkage to the National Patient Register, and examined cannabis use in relation to other illicit drug use and drug use disorders. We found that cannabis use increased the risk of other illicit drug use at three-year follow-up, with the risk being higher for recent cannabis users compared to lifetime users. We also found that cannabis use did not independently increase the risk for subsequent drug use disorders. This link was rather explained by other illicit drug use. In the second study, we used data from the longitudinal population-based Women and Alcohol in Gothenburg (WAG) study to examine associations across time between cannabis use and anxiety and depression. Cannabis potency has increased during the last years, as has the risk of developing adverse cannabis-related health outcomes. We found an association between cannabis use and anxiety in both the oldest and youngest cohorts of women, and between cannabis use and depression in the youngest cohort. Thus, the association between cannabis use and depression among the younger women, examined between 2000 and 2015, became more pronounced when adding the effect of period of use.

In the third study, we focused on improving our knowledge of individuals with cannabis use disorder (CUD), that is harmful use of or dependence on cannabis. By examining national health care registers, we saw that there was an increase of CUD diagnoses in Sweden over time, especially among younger birth cohorts. Individuals with CUD were more often male, from younger birth cohorts, with lower education and income than those without CUD. Also, a majority of those with CUD had an additional psychiatric diagnosis. Men and women with CUD exhibited differences in education, income and psychiatric comorbidity. Our subgroup analysis revealed that the two groups with the highest proportions of CUD, were, on one hand, young men with low income and high proportion of other substance use disorders, and on the other hand, young women with high income and high proportion of behavioral disorders. In the fourth study, we once again utilized national health care registers and examined the extent to which socioeconomic factors and psychiatric disorders affect the risk of CUD readmission into health care. We found that twenty percent readmitted to care during follow-up, and that those with low education, schizophrenia and psychotic disorders, mood-related disorders or personality disorders had the highest risks of readmission. Younger individuals were at highest risk of readmission (aged 18-35 years).

The findings from this thesis provide public health workers and clinicians with scientifically underpinned knowledge regarding the links between cannabis use, other drug use and psychiatric disorders, also demonstrating the impact of socioeconomic factors and psychiatric comorbidity in relation to cannabis use disorder. Our findings may be used to improve cannabis-related care by highlighting individuals with complex healthcare needs, as well as underscoring the importance of comorbidity within psychiatric care.

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