Differentiating Delusions from Obsessions

Core Phenomenological Features to Assess

The American College of Neurology and Psychiatry recommends recognizing obsessions as intrusive, unwanted, and excessive thoughts that the patient actively resists and finds distressing, whereas delusions are fixed false beliefs held with conviction that the patient does not recognize as unreasonable and does not resist 1, 2
Obsessions are accompanied by awareness that the thoughts are inaccurate, excessive, or unreasonable, with the patient recognizing "this doesn't make sense" even while feeling compelled to respond 1, 2
Obsessions generate marked anxiety, distress, or discomfort that the patient finds unpleasant and wants to neutralize 1, 2

The patient should be asked if these thoughts feel like they're intruding against their will, or if they feel like accurate beliefs about reality, to differentiate between obsessions and delusions 3
The patient should be asked if they recognize these thoughts as excessive or unreasonable, even if they can't stop them, to assess for obsession or delusion 3

Compulsions are performed rigidly to neutralize specific obsessive fears, reduce anxiety, or prevent dreaded outcomes, with the patient recognizing them as excessive 1, 3

If OCD is diagnosed, the patient should be initiated on Cognitive Behavioral Therapy with Exposure and Response Prevention (ERP) as first-line treatment, with sertraline 50 mg daily as first-line SSRI for moderate-to-severe symptoms 3, 4
If comorbid OCD and psychotic disorder, both conditions should be addressed, recognizing that severe OCD may secondarily impair functioning but does not cause primary psychotic symptoms 3