Ketamine Users Have High Rates of Psychosis and/or Depression Hua Jun Liang, PhD m Ka Lam Tang, MD m Fu Chan, MD m Gabor Sandor Ungvari, MD, PhD m Wai Kwong Tang, MD Abstract Ketamine has been linked to psychosis and used in the treatment of depression. However, no study has examined the prevalence of psychotic and depressive disorders in dependent ketamine users. This study aimed to examine the frequency of various psychopathologies among a series of patients seeking treatment for ketamine use in Hong Kong, China. The case records of 129 patients with a history of ketamine use receiving treatment at three substance use clinics between January 2008 and August 2012 were retrieved for data collection. Patients’ demographic data, patterns of substance misuse, and comorbid psychiatric diagnoses were recorded and entered into analyses. The mean age of onset and length of ketamine use were 17.7 T 4.4 and 8.7 T 5.7 years, respectively. All patients were dependent on ketamine at the time of data collection. Multiple substance misuse was common. Eighty-four of the 129 (65.1%) patients were found to have comorbid psychiatric disorders, most commonly substance-induced psychotic disorder (31.8%) followed by depressive disorder (27.9%). Psychosis and/or depression were common in ketamine-dependent patients referred to a psychiatric substance use clinic. The findings provide evidence of an association between chronic ketamine use and the presence of psychosis and/or depression. The results raise the issue of safety when using ketamine in the long-term treatment of depression. Keywords: depression, ketamine, psychosis BACKGROUND The search for a safe and potent anesthetic led to the devel- opment of arylcyclohexylamines such as phencyclidine (PCP) and ketamine in the late 1950s. These drugs are still widely used today (Guldner, Petinaux, Clemens, Foster, & Antoine, 2006; Restall, Tully, Ward, & Kidd, 1988; World Health Orga- nization, 2011). Since the recreational use of ketamine was first reported on the West Coast of the United States inthe 1970s, it has become one of the most frequently used drugs, particularly among young people and club-goers (Gahlinger, 2004; McCambridge, Winstock, Hunt, & Mitcheson, 2007; Narcotics Division, Security Bureau, Government of Hong Kong Special Administrative Region of the People’s Republic of China, 2012). In the United States, ketamine was first reported on the club scene in the early 1990s appearing both as a constituent of ecstasy pills and independently as ‘‘K’’ or ‘‘Special K’’ (Jansen, 1993). Within a very short time, ketamine has become increasingly prevalent in United Kingdom, partic- ularly in the club and underground music scene (McCambridge et al., 2007). In an online questionnaire survey involving 3,806 participants in the United Kingdom, 33.8% of respondents reported ketamine use within the past year, and 17% were de- pendent on ketamine (Winstock, Mitcheson, Gillatt, & Cottrell, 2012). In 2003, a national survey in Australia reported that 40% of ‘‘party drug users’’ used ketamine (Breen et al., 2004). A study from Taiwan reported that ketamine was detected in 47% of urine samples of rave party attenders (Lua, Lin, Tseng, Hu, & Yeh, 2003). Since 2005, ketamine has been the most common substance used by Hong Kong teenagers (Nar- cotics Division, Security Bureau, Government of Hong Kong Special Administrative Region of the People’s Republic of China, 2009), and ketamine-related poisoning contributed to 7.1% of the 4,500 cases of poisoning in 2010 (Chan, Tse, & Lau, 2012). Ketamine was the preferred drug among young people at Hong Kong rave parties and social gatherings (Wong et al., 2009). To summarize, ketamine use has become highly prevalent and very popular among certain populations and subgroups around the world, particularly adolescent and young adult club-goers. Ketamine’s potential for inducing psychiatric disturbances has been known since it was first introduced as a prescription drug. Acute ketamine administration induces schizophrenia- like symptoms and impairs cognitive functions in both healthy volunteers (Malhotra et al., 1996) and patients with schizophrenia (Malhotra et al., 1997). Even at subanesthetic doses, ketamine Hua Jun Liang, PhD, and Wai Kwong Tang, MD, Department of Psychi- atry, The Chinese University of Hong Kong, Hong Kong SAR, China. Ka Lam Tang, MD, Department of Psychiatry, Prince of Wales Hospital, Hong Kong SAR, China. Fu Chan, MD, Department of Psychiatry, North District Hospital, Hong Kong SAR, China. Gabor Sandor Ungvari, MD, PhD, School of Psychiatry & Clinical Neuro- science, University of Western Australia, and University of Notre Dame/ Marian Centre, Perth, Australia. The authors report no conflicts of interest. The authors alone are re- sponsible for the content and writing of this article. Correspondence related to content to: Wai Kwong Tang, MD, Depart- ment of Psychiatry, The Chinese University of Hong Kong, 7th Floor, Shatin Hospital, 33 A. Kung Kok Street, Ma On Shan, New Territories, Hong Kong SAR, China. E-mail: tangwk@cuhk.edu.hk DOI: 10.1097/JAN.0000000000000060 8 www.journalofaddictionsnursing.com January/March 2015 Original Article Journal of Addictions Nursing & Volume 26 & Number 1, 8Y13 & Copyright B 2015 International Nurses Society on Addictions Copyright © 2015 International Nurses Society on Addictions. Unauthorized reproduction of this article is prohibited.