Evidence Base for Interpersonal Psychotherapy for Bulimia Nervosa
The evidence supporting the effectiveness of IPT for the treatment of BN is ample. To date, cognitive-behavioral therapy (CBT) is the most- researched, best-established treatment for BN (Wilson, Grilo, & Vitousek, 2007). However, IPT is the only psychological treatment for BN that has demonstrated long-term outcomes that are comparable to those of CBT (Wilson & Shafran, 2005). Currently, all controlled studies of IPT for BN have been comparison studies with CBT. Initially, similar short- and longterm outcomes for binge eating remission between CBT and IPT were reported (Fairburn et al., 1993, 1995). In a subsequent multisite study, Agras, Walsh, Fairburn, Wilson, and Kraemer (2000) compared CBT and IPT as treatments for BN. At the end of treatment, clients receiving CBT showed significantly higher rates of abstinence from binge eating and lower rates of purging than those receiving IPT. However, by 8- and 12-month follow-ups, the two treatments no longer differed significantly in outcome. Clients receiving CBT had maintained their progress or slightly worsened, and clients receiving IPT had experienced slight improvements. The initial, more impressive effect of CBT compared with IPT may be partially explained by a relative lack of focus on ED symptomatology in the research version of individual IPT for BN. A potential advantage of IPT may be that many clients with BN perceive the interpersonal focus of IPT as particularly relevant to their ED and to their treatment needs, perhaps more so than a cognitive-behavioral focus on distortions related to weight and shape; indeed, IPT clients rated their treatment as more suitable and expected greater success than did CBT clients. Currently, IPT is considered an alternative to CBT for the treatment of BN (Wilson et al, 2007). Counselors have been recommended to inform clients of the slower response time for improvements compared with CBT (Wilson, 2005). However, we contend that when interpersonal problems are consistently linked to ED symptoms in IPT, response to treatment will likely occur more rapidly.
An emerging literature has provided some insight into predictors of success with IPT for the treatment of EDs. Chui, Safer, Bryson, Agras, and Wilson (2007) reported that although clients in their large multicenter trial responded with higher abstinence rates when randomized to CBT as opposed to IPT, African American female participants showed greater reductions in binge eating episode frequency when treated with IPT than with CBT. This finding suggests that IPT may be particularly appropriate for African American women with BN and speaks to the need for further study of IPT with different racial and ethnic groups. Because therapeutic alliance is associated with treatment outcome, researchers from this same study examined clients' expectation of improvement (Constantino, Arnow, Blasey, & Agras, 2005). They found that expectation of improvement was positively associated with outcome for both CBT and IPT, emphasizing the important role of client expectations in both treatments. Finally, in a study of postremission predictors of relapse, Keel, Dorer, Franko, Jackson, and Herzog (2005) found that for women with BN, worse psychosocial functioning was associated with a greater risk for relapse, which, they posited, may partly help to explain the long-term effectiveness of IPT for BN.