Why Most Depression Is Unipolar

Why is unipolar depression so much more common than bipolar disorder — and what keeps most depressed brains from swinging into mania? This episode unpacks the biology behind the prevalence gap. We explore heritability differences (bipolar is 60-85% genetic, unipolar ~37%), structural brain distinctions like prefrontal cortex thinning in the pars orbitalis and pars triangularis, and the dopamine surge unique to mania. We also examine the messy overlap: 40-60% of bipolar patients are initially misdiagnosed with unipolar depression, and ADHD’s emotional lability can muddy the picture further. If you’ve wondered whether your own depression is “just” unipolar or something more, this episode gives you the neurobiological framework to tell the difference.