Affective disorders are among the most debilitating psychiatric conditions and afflict 20% of the population while contributing to significant morbidity and mortality.1 The association between cannabis use and unipolar depression has been well documented, as individuals with cannabis dependence are almost three times more likely to suffer from depressive disorders than the general population.2 Those with depressive conditions are in turn twice as likely to use cannabis than the general population.3 In patients with bipolar depression, much of the same is true.4
In one longitudinal study by Henquet and colleagues,5 cannabis use at baseline predicted an increased risk of manic symptoms at the three-year follow-up. There is now also evidence from longitudinal population-based studies that suggest long-term cannabis use is associated with increased risk of suicidal ideation, suicide attempt, and death by suicide in a dose-dependent manner.6
According to the National Academy of Sciences, Engineering, and Medicine report,7 which summarizes the most comprehensive state of evidence regarding the health impacts of cannabis, there is a moderate level of evidence to support that cannabis use is associated with increased risk of developing depressive disorders; increased incidence of suicidal ideation and behavior (attempts as well as completion, particularly in heavy users); and increased symptoms of mania and hypomania in users with bipolar disorder. Limited evidence from statistical association raises concern that cannabis use increases the likelihood of developing bipolar disorder.8
The role of the endocannabinoid system has been of interest since the 1990s when it was first discovered. A reduction in serum levels of 2-arachidonoylglycerol, one of the endocannabinoids, has been noted in females diagnosed with major depressive disorder.9 Postmortem studies have also demonstrated variabilities in cannabinoid receptor type 1 density and mRNA levels in the dorsolateral prefrontal cortex of those with depression who died by suicide.10 There is abundant further evidence to support that deficiency and overall dysregulation in endocannabinoid signaling is implicated in the pathophysiology of affective disorders.
The only randomized controlled trials of cannabinoids in humans for affective disorders are rather limited and date back to the 1970s.11,12 Here the investigators attempted to use oral tetrahydrocannabinol (THC) only in the treatment of unipolar and bipolar depressive disorders. Not only was there a complete failure of an antidepressant response, but also poor tolerability was demonstrated in the form of dysphoric, psychotic, and anxiety reactions.
In a study by Kotin and colleagues,11 eight psychotropic-free hospitalized patients (four with bipolar depression and four with unipolar major depression) received under double blind conditions a seven-day course of placebo, followed by a seven-day course of twice daily oral THC 0.3 mg/kg, and then seven days of placebo. There was a 50% dropout during the THC treatment phase due to adverse effects such as severe anxiety attacks and depersonalization presenting as early as the first dose.
In a study by Ablon and Goodwin,12 13 hospitalized patients (five with bipolar depression and eight with unipolar major depression) were observed for 3 weeks and subsequently received, under double blind conditions, either oral THC titrated from 5 mg daily up to 20 mg twice daily or placebo. Seven participants experienced dysphoric reactions and six had to drop out due to panic reactions or psychotic disturbances, which occurred as early as the first dose.
Clinical bottom line
There is much to be learned about the exact implication of the endocannabinoid system in mental health symptoms and overall clinical conditions. However, the current body of available knowledge certainly suggests involvement. Although the majority of data provide mere association, if one accepts the implied bidirectional relationship, there is significant concern of harm in individuals with affective disorders and cannabis use should be discouraged.
Although a better understanding of the endocannabinoid system may unveil pharmacotherapeutic targets, this is likely years away. To expedite this, pharmaceutical-grade cannabinoids are now available and should be utilized in furthering such research.
At this point, all organizations for mental health have issued warnings discouraging endorsement of cannabis use in general, as well as for attempts at management of any mental health clinical conditions. As clinicians, we need to be well versed with the above data in order to have meaningful conversations with our patients who are cannabis users or contemplate use.
Dr Stanciu is Assistant Professor of Psychiatry at Dartmouth’s Geisel School of Medicine and Director of Addiction Services at New Hampshire Hospital, Concord, NH. Dr Teja is a PGY-4 General Psychiatry Resident at Dartmouth’s Geisel School of Medicine, Hanover, NH. The authors report no conflicts of interest concerning the subject matter of this article.
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