Does cannabis help or worsen depression?

The cannabis-depression relationship is bidirectional and complex. Cross-sectional studies consistently show higher rates of depression in cannabis users, but causality is difficult to establish — people with depression may self-medicate with cannabis. Longitudinal evidence: a 2014 meta-analysis (Mammen & George) found heavy cannabis use associated with increased risk of developing depression (OR 1.62), with stronger effects in adolescent-onset users. Mechanism for worsening: chronic THC use downregulates CB1 receptors and reduces anandamide tone, potentially worsening mood regulation. Acute THC can cause dysphoria, particularly at high doses or in anxious individuals. Potential benefit: CBD has antidepressant-like effects in animal models via 5-HT1A activation and neurogenesis promotion. One small human study found CBD reduced depressive symptoms. For patients with comorbid depression and anxiety, the net effect of cannabis depends heavily on THC:CBD ratio, dose, frequency, and individual vulnerability. Current evidence does not support cannabis as a depression treatment.