What is the effect of cannabis on mood in adults with a history of mood disorders, such as depression or bipolar disorder?

Cannabis Has Harmful Effects on Mood in Adults with Mood Disorders

Cannabis use is associated with increased risk for developing depressive disorders, exacerbates existing psychiatric disorders in vulnerable individuals, and is linked to unfavorable prognosis in both major depressive disorder and bipolar disorder—therefore, cannabis should be avoided in adults with a history of mood disorders. 1, 2, 3

Primary Psychiatric Risks

Depression

• Cannabis use increases the risk of developing major depressive disorder and worsens depressive symptoms in the general population 3
• While users may perceive a 50% reduction in depression symptoms acutely, continued cannabis use appears to exacerbate baseline symptoms of depression over time 4
• The American Psychiatric Association notes that cannabis may be associated with increased risk for developing depressive disorders and may exacerbate existing psychiatric disorders in vulnerable individuals 1

Bipolar Disorder

• Cannabis use is linked to poorer clinical course in bipolar disorder, with evidence suggesting an increase in hypomanic days 5, 6
• The literature consistently demonstrates that cannabis use is associated with an unfavorable prognosis in bipolar disorder 3
• Cannabis worsens positive psychotic symptoms and total psychiatric symptoms in patients being treated for psychosis, fundamentally undermining antipsychotic treatment goals 2

Mechanism of Harm

Direct Neuropsychiatric Effects

• High doses of THC are specifically associated with psychotic symptoms and can precipitate severe anxiety, especially in vulnerable individuals 1, 2, 7
• Cannabis causes changes in glutamate and dopamine signaling that contribute to cognitive deficits and psychosis risk 1
• The heightened risk for transition to schizophrenia and psychosis is particularly concerning in those with pre-existing mood disorders 1

Medication Interactions

• Cannabis can potentiate the unwanted side effects of anxiety medications, creating a dangerous synergistic effect 2
• High doses of THC directly counteract the therapeutic effects of antipsychotic medications in vulnerable individuals 2
• The American Society of Clinical Oncology recommends that cannabis should not be prescribed as treatment for anxiety disorders due to lack of proven benefits and well-documented risks 2

Critical Potency Considerations

Increasing THC Concentrations

• The potency of cannabis products has dramatically increased, with average THC concentration almost doubling from 9% in 2008 to 17% in 2017, significantly elevating all psychiatric risks 1, 2
• Cannabis concentrates may have THC levels as high as 70%, which intensifies adverse health effects 1
• This increasing potency significantly elevates all risks for medication interactions and psychiatric destabilization 2

Additional Complications

Cannabis Use Disorder

• Approximately 10% of adults with chronic cannabis use develop cannabis use disorder, characterized by clinically significant impairment that complicates psychiatric treatment 1, 2, 7
• Patients with mood disorders have higher rates of cannabis use and cannabis use disorder compared to the general population 8
• A randomized trial found that participants who received a medical cannabis card had almost twice the incidence of developing cannabis use disorder within 12 weeks 1

Cognitive Impairment

• Chronic cannabis use causes persistent cognitive deficits including impaired verbal learning and memory, deficits in attention and executive function, and reduced processing speed 1, 7
• These cognitive effects compound the functional impairment already present in mood disorders 1

Clinical Recommendations

Absolute Contraindications

• Cannabis should be avoided entirely if there is a history of psychotic episodes or breaks with reality 2, 7
• The treatment focus should center on cannabis cessation for patients with bipolar disorder or psychotic disorders who are using cannabis while on psychiatric medications 2

Risk Counseling

• Patients using cannabis while on psychiatric medications experience increased risk for behavioral health issues, including anxiety and depression 2
• Healthcare providers should counsel patients that while cannabis may provide perceived short-term relief of negative affect, continued use worsens baseline mood symptoms over time 4, 3

Common Pitfalls to Avoid

• Do not rely on patient self-reports of therapeutic benefit—subjective reports by patients suggest an overall positive effect, but prospective data shows worsening of baseline symptoms over time 4, 6
• Do not assume that CBD-predominant products are safe—high CBD/low THC cannabis still affects mood and carries risks 4
• Do not underestimate the risk of cannabis use disorder development, particularly in patients with mood disorders who already have higher baseline rates 8, 3