Moderators of treatment effect in a randomised controlled trial of single‐ and multi‐family therapy for anorexia nervosa in adolescents and emerging adults

Introduction Multi‐family therapy for anorexia nervosa (MFT‐AN) is a novel, group‐based intervention that intensifies single‐family therapy for anorexia nervosa (FT‐AN), with the aim of improving outcomes. The current study explored treatment moderators in a randomised controlled trial ( N = 167) of FT‐AN and MFT‐AN for young people (adolescents/emerging adults aged 13–20 years) with anorexia nervosa. Methods Data were analysed using multiple linear regression. Six hypothesised baseline participant and parent factors were tested as possible moderators of treatment effect on end‐of‐treatment and follow‐up percentage of median Body Mass Index (%mBMI); age, eating disorder symptom severity, perceived family conflict (young person and parent ratings) and parent‐rated experiences of caregiving (positive and negative). Results Greater parent‐rated positive caregiving experiences moderated treatment outcomes at follow‐up ( β = −0.47, 95%CI: −0.91, −0.03, p = 0.04), but not end‐of‐treatment. Participants who had fewer parent‐rated positive caregiving experiences at baseline had higher weight at follow‐up if they had MFT‐AN compared to FT‐AN. No other hypothesised baseline factors moderated treatment outcome ( p 's > 0.05). Discussion The current study suggests MFT‐AN may be indicated for families who present with fewer positive caregiving experiences to treatment. The MFT‐AN group context may help to promote mentalisation and hope for these families, which may be harder to achieve in single‐family treatment. Future research is needed to empirically evaluate how and why MFT‐AN supports this group more. Trial Registration ISRCTN registry: ISRCTN11275465, registered 29 January 2007.