Dual diagnosis means a person is living with a mental health condition and a substance use disorder at the same time. Depression alongside alcohol use, anxiety alongside opioid use, PTSD alongside stimulant use: these pairings are common, not rare. When you or your loved one walks into addiction treatment, treating only one side tends to leave the other pulling the ground out from under it. Real progress comes from caring for both conditions together, at the same time, with attention to how each one shapes the other.