Intrusive thoughts are unwanted, involuntary thoughts, images, or unpleasant ideas that may become an obsession, is upsetting or distressing, and can feel difficult to manage or eliminate. They are predominantly associated with Obsessive Compulsive Disorder (OCD), but they are often seen amongst the symptoms of other anxiety disorders. Intrusive thoughts, urges, and images are of inappropriate things at inappropriate times, and generally have aggressive, sexual, or blasphemous themes. Intrusive thoughts are not unique to people who are struggling with a mental health concern(s) .

When intrusive thoughts occur with OCD, patients are less able to ignore the unpleasant thoughts and may pay undue attention to them, causing the thoughts to become more frequent and distressing. Attempting to suppress intrusive thoughts often causes these same thoughts to become more intense and persistent. The thoughts may become obsessions that are paralyzing, severe, and constantly present, these might involve topics such as violence, sex, or religious blasphemy, among others.

Intrusive thoughts are associated with OCD or OCPD, but may also occur with other conditions such as post-traumatic stress disorder, clinical depression, postpartum depression, generalized anxiety disorder, and anxiety.