Overview
Intrusive thoughts refer to thoughts that interrupt a flow of thoughts. There are some wordier definitions that sound more technical, but that’s the essence of it. In clinical literature, it’s common to see intrusive thoughts referred to as “obsessions”, “mental intrusions”, or other close synonyms. Everyone has some level of intrusive thoughts that come to mind throughout their day and life, but it can reach a pathological level as symptoms of a disorder that would benefit from medical treatment.
From the American Psychological Association’s Dictionary of Psychology:
mental events that interrupt the flow of task-related thoughts in spite of efforts to avoid them. Minor intrusions are normal and widespread (see mind wandering). Upsetting intrusions are common after trauma and in obsessive-compulsive disorder. 1
The phrase “intrusive thoughts” appears in the DSM-5-TR as a symptom of a myriad of conditions that, as mentioned in the APA definition, include OCD and PTSD, but also dissociative disorders and anxiety disorders. The DSM-5-TR doesn’t provide a definition for intrusive thoughts, though.