Inpatient treatment for patients with bulimia nervosa (BN) is recommended in extreme or severe cases and/or after failure of outpatient treatment and is highly effective. However, a number of patients show symptom increase and relapse after discharge. The aim of this study is to evaluate the efficacy of a guided smartphone-based aftercare intervention following inpatient treatment of patients with BN to support recovery.

Bulimia nervosa (BN) is a severe mental disorder characterized by recurrent episodes of binge eating and recurrent inappropriate compensatory behaviors to prevent weight gain. Evidence-based psychological treatments exist, however, even if treatment is successful in reducing behaviors such as binge eating and purging, abstinence rates may remain low and even if remission or abstinence have been received after treatment relapse rates are substantial. There is evidence that the stability of remission increases if the corresponding symptom improvement lasts at least for 4 months. Studies on the effectiveness of inpatient treatment in adult patients with BN show responder rates of up to 77%. However, it is often difficult for patients to maintain therapy success after discharge, as relapse rates reach up to 40% with the highest risk during the first 5 or 6 months after remission. There is preliminary evidence for efficacy regarding the potential of technology-based interventions in aftercare for patients with BN. However, so far, there is no study evaluating a smartphone-based aftercare intervention for patients with BN. Therefore, the aim of this study is to investigate the efficacy of a guided smartphone-based aftercare intervention as an add-on element to treatment as usual (TAU) compared to TAU alone in inpatients with BN. Our primary hypothesis is that the intervention group shows a significantly higher remission rate than TAU at end of treatment.

Eligible patients with BN who are discharged from inpatient treatment will be randomized either to receive a 4-month smartphone-based aftercare intervention with therapist feedback as an add-on element to treatment as usual (TAU) or TAU alone. Assessment points will be as follows: at hospital discharge (=baseline, T0), 16 weeks (=end of the aftercare intervention, T1) and after 10 months (=6-month follow-up, T2).

Inclusion Criteria:

1. primary diagnosis of BN (DSM-5: 307.51) at admission as assessed by the diagnostically relevant items from the Eating Disorder Examination (Hilbert et al. 2016b),
2. sex: female,
3. age: from 13 years onwards to 60 years,
4. regular completion of inpatient treatment,
5. at least a length of inpatient stay of 6 weeks,
6. remission defined as less than once a week of binge eating and compensatory behavior in the past 28 days thus no longer meeting the full criteria for BN according to DSM-5,
7. owner of a smartphone,
8. informed consent of the patient and, in case of minors, also of the parents.

Exclusion Criteria:

1. major depression (Beck Depression Inventory-II (BDI-II) > 29 at discharge),
2. suicidal tendency (item 9 of BDI-II > 1 at discharge),
3. very high level of care after inpatient treatment (e.g. therapeutic living community, day clinic),
4. pregnancy.