Abstract: We included 25 trials in this version of the review (13 from the original 2010 review and 12 newly-included studies). Sixteen trials were of adolescents, eight trials of adults (seven of these in young adults aged up to 26 years) and one trial included three age groups: one adolescent, one young adult and one adult. Most investigated family-based therapy or variants. Reporting of trial conduct was generally inadequate, so that in a large number of studies we rated the risk of bias as unclear for many of the domains. Selective reporting bias was particularly problematic, with 68% of studies rated at high risk of bias in this area, followed by incomplete outcome data, with 44% of studies rated at high risk of bias in this area. For the main outcome measure of remission there was some low-quality evidence (from only two studies, 81 participants) suggesting that family therapy approaches might offer some advantage over treatment as usual on rates of remission, post intervention (risk ratio (RR) 3.50, 95% confidence interval (CI) 1.49 to 8.23; I2 = 0%). However, at follow-up, low-quality evidence from only one study suggested this effect was not maintained. There was very low-quality evidence from only one trial, which means it is difficult to determine whether family therapy approaches offer any advantage over educational interventions for remission (RR 9.00, 95% CI 0.53 to 153.79; 1 study, N = 30). Similarly, there was very low-quality evidence from only five trials for remission post-intervention, again meaning that it is difficult to determine whether there is any advantage of family therapy approaches over psychological interventions (RR 1.22, 95% CI 0.89 to 1.67; participants = 252; studies = 5; I2 = 37%) and at long-term follow-up (RR 1.08, 95% CI 0.91 to 1.28; participants = 200; studies = 4 with 1 of these contributing 3 pairwise comparisons for different age groups; I2 = 0%). There was no indication that the age group had any impact on the overall treatment effect; however, it should be noted that there were very few trials undertaken in adults, with the age range of adult studies included in this analysis from 20 to 27. There was some evidence of a small effect favouring family based therapy compared with other psychological interventions in terms of weight gain post-intervention (standardised mean difference (SMD) 0.32, 95% CI 0.01 to 0.63; participants = 210; studies = 4 with 1 of these contributing 3 pairwise comparisons for different age groups; I2 = 11%) . Overall, there was insufficient evidence to determine whether there were any differences between groups across all comparisons for most of the secondary outcomes (weight, eating disorder psychopathology, dropouts, relapse, or family functioning measures), either at post-intervention or at follow-up. There is a limited amount of low-quality evidence to suggest that family therapy approaches may be effective compared to treatment as usual in the short term. This finding is based on two trials that included only a small number of participants, and both had issues about potential bias. There is insufficient evidence to determine whether there is an advantage of family therapy approaches in people of any age compared to educational interventions (one study, very low quality) or other psychological therapies (five studies, very low quality). Most studies contributing to this finding were undertaken in adolescents and youth. There are clear potential impacts on how family therapy approaches might be delivered to different age groups and further work is required to understand what the resulting effects on treatment efficacy might be. There is insufficient evidence to determine whether one type of family therapy approach is more effective than another. The field would benefit from further large, well-conducted trials.

Plain-language summary: We included 25 trials in the review. Fourteen trials used family-based therapy, one used systems family therapy, one used structural family therapy and seven studies used therapy with family involvement but did not provide specific details about the theory behind the therapy or its procedures, termed other family therapy. Two studies included two family therapy arms each: one included family-based therapy and systems family therapy arms, and one included systems family therapy and other family therapy arms. Four studies compared family therapy approaches to treatment as usual, six compared family therapy approaches to other psychological interventions and two compared family therapy to educational interventions. Twelve studies compared various forms of family therapy approaches to each other. Two studies included both a treatment as usual as well as other psychological intervention arms. Overall there was some low-quality evidence from only two trials to suggest that family therapy approaches may be better than treatment as usual in the short term. The size and very low quality of the evidence base and the consistency of the trial outcomes are insufficient at this time to draw conclusions about whether family therapy approaches offer any clear advantage over educational or psychological interventions. We found very few differences between treatment groups on measures of weight, eating disorder symptoms and family functioning, and these differences were generally not maintained at follow-up. The reporting of death rates was not clear enough to assess whether death is reduced for those treated with family therapy approaches compared to other interventions. There was very little information about the effects of the interventions on general or family functioning. The way the trials were run was not adequately described in many studies and we found potential risks of bias in most of the studies. This limited the meaningful conclusions that we could draw from the studies. Overall, there is a very limited evidence base in this field. There is some low-quality evidence to suggest that family therapy approaches may be effective compared to treatment as usual in the short term. There is insufficient evidence to be able to determine whether family therapy approaches offer any advantage over educational interventions, other types of psychological therapy, or whether one type of family therapy approach is more effective than another. Most of the studies contributing to the findings were undertaken in adolescents and young adults. There are clear implications about how family therapy approaches might be delivered to different age groups, and we need further research to understand what the resulting effects on treatment might be.