Associations of ketamine use with mental health and substance use outcomes at 12 months follow-up in young Europeans

Background: In the last decade ketamine has been investigated for its potential as a treatment of depression and substance use (Morgan & Curran, 2012; Katalinic et al., 2013). At the same time ketamine is used recreationally and chronic recreational use might be associated with detrimental outcomes such as addiction, neurocognitive impairment and depressed mood (Morgan et al., 2010). Given a recent increase by 100% of ketamine use in the United Kingdom more information on the long-term effects of ketamine are imminent (Home Office (2018)), especially in the light of its potential introduction as a therapeutic treatment in the near future.

In the current study we would like to investigate how frequency of baseline ketamine use is associated with mental health and problematic substance use at 12 month follow up using online survey data from 5 European countries. To tease out the effect of polysubstance use, ketamine users and controls will be matched on confounding variables using propensity scores. We would furthermore like to elucidate how changes in frequency of ketamine use over 12 months affect mental health and substance use outcomes.

Methods: In order to take part in the baseline survey participants had to live in one of the above countries at baseline, be between 18-34 years old and indicate participation in at least 6 dance/electronic music events in the last 12 months. Participants who completed the baseline survey were invited via email to complete the follow-up survey exactly 12 months after completion of the baseline survey.

Sample: N=8000 participants from five countries (Belgium, Italy, Netherlands, Sweden & United Kingdom) completed the Electronic Music Scene baseline survey between May-November 2017 and almost 3000 participants completed the follow-up survey between May 2018-November 2018. In the baseline survey 926 participants indicated ever use of ketamine and 744 participants indicated ketamine use within the last 12 months. In the follow-up survey 902 participants indicated ketamine use within the last 12 months.

Planned Analyses:

A protocol for the analyses was pre-registered on OSF prior to the end of follow-up data collection (link: https://osf.io/zecy3/, for more detail). The analysis is currently being conducted.

Analysis 1) Propensity scores will be used to match ketamine users (use within past 12 months at baseline) with never users on demographic variables and other drug use variables, grouped by heaviness of ketamine use frequency. We hypothesise a difference between high frequency ketamine users and matched non-users and no difference between low-frequency ketamine users and matched non-users in PHO-2 and GAD-2 scores at follow-up. Furthermore differences in problematic alcohol and substance use outcomes will be compared. Groups will be compared using linear regression.

Analysis 2) Associations between changes of ketamine use and a changes in mental health outcomes will be investigated. We expect a ‘dose-response’ relationship where an increase in use is related to greater mental health problems and a decrease in use is related to a reduction of mental health problems. Furthermore associations between ketmaine use and in problematic alcohol and substance use outcomes will be assessed.