Heavy cannabis use, dependence and the brain : a clinical perspective

Emese Kroon, Lauren Kuhns, Eva Hoch & Janna Cousijn

Addictions, 2019, 1-12.

doi : 10.1111/add.14776

 

ABSTRACT

Aims : To summarize and evaluate our knowledge of the relationship between heavy cannabis use, cannabis use disorder (CUD) and the brain.

Methods : Narrative review of relevant literature identified through existing systematic reviews, meta-analyses and a PubMed search. Epidemiology, clinical representations, potential causal mechanisms, assessments, treatment and prognosis are discussed.

Results : Although causality is unclear, heavy and dependent cannabis use is consistently associated with a high prevalence of comorbid psychiatric disorders and learning and memory impairments that seem to recover after a period of abstinence. Evidence regarding other cognitive domains and neurological consequences, including cerebrovascular events, is limited and inconsistent. Abstinence after treatment is only achieved in a minority of cases; treatment targeted at reduction in use appears have some success. Potential moderators of the impact of CUD on the brain include age of onset, heaviness of use, CUD severity, the ratio of 9-tetrahydrocannabinol to cannabidiol and severity of comorbid disorders.

Conclusions : Current evidence of long-term effects of daily cannabis use and cannabis use disorder
on brain-related outcomes is suggestive rather than conclusive, but use is associated with psychiatric morbidity and with cognitive impairments that recover after a period of abstinence.

Keywords : brain, cannabis use disorder, cognition, neurological disorders, review, treatment.

INTRODUCTION

This narrative review summarizes our knowledge of the relation between heavy cannabis use [defined as (near) daily use], cannabis use disorder (CUD) and the brain. Cannabis contains more than 100 different cannabinoids [1], of which 9-tetrahydrocannabinol (THC) and cannabidiol (CBD) are the most studied. THC is the main psychoactive cannabinoid responsible for the cannabis ‘high’ and addictive potential. CBD has been suggested to ameliorate THC effects while having little psychoactive effect on its own [2]. Aside from plant-based cannabis products, synthetic cannabinoids mimic the effects of THC. Given the scope of this review, the limited evidence on the effects of synthetic cannabinoids and the chemical differences between plantbased and synthetic cannabinoids, we will only discuss the effects of plant-based cannabis products unless otherwise specified.

Although CUD is one of the most common substance use disorders (SUDs), effects of CUD on the brain are still rarely studied. Daily cannabis use has been established as one of the best predictors of CUD. As such, findings from heavy users and, where possible, individuals with a diagnosed CUD will be evaluated. After a brief epidemiological overview, clinical representations, potential causal mechanisms, assessments, treatment and prognosis will be discussed. Table 1 provides a summary of the acute and long-term effects of heavy cannabis use and CUD on brain structure, cognition, psychiatric comorbidities and neurological disorders.

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Kroon_et_al-2019-Addiction