Long-Term Ketamine Self-Injections in Major Depressive Disorder: Focus on Tolerance in Ketamine's Antidepressant Response and the Development of Ketamine Addiction.

Sub-anaesthetic ketamine is of special interest for depression research due to its rapid and potent but short-lived antidepressant response (after-effect). The presented case is the first one in the literature which deals in detail with the transfer from ketamine's antidepressant action to ketamine addiction. A 50-year-old anaesthetic nurse, who had never been treated with antidepressants before, started with self-injecting ketamine racemate 50 mg IM once a week to cope with her major depression. She continuously stole ketamine from hospital stocks. Due to a gradually developing tolerance to ketamine's antidepressant action, she stepwise increased dose and frequency of ketamine self-injections up to daily 2 g IM (three-fold her anaesthetic dose) over six months. This was accompanied by the development of ketamine addiction, loss of consciousness, dissociative immobility, and amnesia. Inpatient detoxification treatment was characterized by a strong craving for ketamine and, later on, by the occurrence of a severe depressive episode remitting on venlafaxine. A 14-week follow-up documented a normal condition without any ketamine sequelae, such as craving, psychosis, depression, or cognitive abnormalities. Thus, awareness of ketamine addiction potential, even in patients who received ketamine for antidepressant purposes, is important.