Overview
“Brain fog” is a term commonly used to describe some combination of confusion, difficulty thinking, and lack of ability to focus. The term gained fresh momentum in the wake of COVID-19, when it was both a highly publicized symptom of long COVID and discussed alongside a spike in substance use disorder cases defined by a dysregulated state of altered consciousness. Since then, there has been a renewed wave of interest in examining brain fog as one of many symptoms impacting someone’s quality of life that can persist after someone has supposedly been cured of a conventional disease like the flu.
The National Center for Biotechnology Information defines it as
“a type of transient cognitive dysfunction that comprises a constellation of symptoms that impair intellectual functioning to a level that interferes with daily activities, commonly including forgetfulness, mental slowness, difficulty thinking or focusing, a perceived slowing of mental processing speed, inability to find the right words, a sensation that the mind went blank or is “cloudy”. Brain fog tends to recur and may be triggered by factors such as physical fatigue, lack of sleep, and prolonged standing or may appear to occur spontaneously.” [^0]
The International Classification of Diseases for Mortality and Morbidity Statistics (ICD-11) defines a related term through “clouding of consciousness,” which means
“An impairment in the clarity of consciousness characterised by impaired ability to comprehend aspects of the environment or the self in relation to the environment, inattention, and abnormalities in thought processes, comprehension. It is typically accompanied by subjective experience of mental clouding described as feeling ‘foggy’. Clouding of consciousness is a common form of cognitive disturbance in Delirium, but it is not synonymous with Delirium because Delirium includes additional diagnostic requirements.” [^1]
For those with substance use disorders, brain fog is extremely common in early recovery, not just from chronic substance use but as a side effect of prescribed medications. Drugs that alter the brain’s dopamine pathways and reward mechanisms directly impact one’s capacity for motivation and concentration, the lack of which can feel like brain fog. Disorders and conditions that commonly co-occur with substance like chronic pain are also associated with brain fog.
Brain fog should not be confused with depersonalization, which can involve the persistent feeling that one is in a dream, or with drowsiness and fatigue, though attempting to work through brain fog can certainly produce exhaustion. Someone with brain fog can be quite awake and physically energized, but struggle to summon the focus needed to chain together a complex train of thought or retrieve memories required for daily tasks.
History and Etymology
Georg Greiner was among the first to connect the concept of a “clouding of consciousness”, or Verdunkelung des Bewussteins in German, to the condition of delirium. It wasn’t uncommon then to see the term associated with severe disturbances like entering a coma.