N-acetyl cysteine does not modify cognitive markers of compulsivity and impulsivity in an ‘at-risk’ eating-disorder group

N-acetyl cysteine (NAC) is a dietary supplement and glutathione precursor which has shown benefit in the treatment of psychiatric disorders that feature prominent compulsive behaviours such as excoriation and trichotillomania [1]. Eating disorders such as anorexia nervosa and bulimia nervosa also possess compulsive features: both in terms of observed symptoms (binge eating, compulsive exercise, compulsive body-checking), as well as their profile on psychological tasks assessing compulsivity [2]. The aim of this study was to investigate whether performance on cognitive tasks measuring compulsivity, or the related construct of impulsivity [3], could be altered using sub-acute dosing of N-acetyl cysteine in a non-clinical participant group enriched for eating disorder symptomatology. We used a randomised, placebo-controlled, cross-over design with 23 participants (females aged 18-40), who were selected to score between 9 and 19 on the EAT-26 questionnaire [3]. All participants had a BMI of over 18.5, were not taking any psychotropic medication and did not have any formal current psychiatric disorders. Participants received 9 days of either NAC or placebo in randomised order, with a seven-day wash-out period in between. The dose was 1200mg for the first two days, followed by 2400mg for the remaining 7 days. At the end of each 9 day drug/placebo administration period participants completed questionnaires and a number of cognitive tasks. Data were analysed using mixed models, with condition (NAC/Placebo) and order (NAC first or Placebo first) as fixed effects, and participant as a random effect. This was specified in R syntax as lmer(y~order*condition + (1| participants)). Task outcome measures were z-scored. There was no significant main effect of condition on the primary task outcome measure, which was defined as perseverative errors on the WCST: F (1,20) = 1.05, p =0.317. Additionally, there was no significant main effect of condition in the MANOVA of key task outcome measures: F (6,35) = 0.599, p =0.729, see table 1 for data.