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Abstract

Background
In clinical practice, olanzapine is commonly used in young people with anorexia nervosa, although the underpinning evidence-base is limited. However, its efficacy, tolerability, acceptability and adherence rate, and the patients’, carers’ and clinicians’ views of olanzapine treatment are unclear. This synopsis article summarises the methods and results of the OPEN feasibility study, overarching the findings and drawing comprehensive conclusions from a quantitative feasibility outcome paper and two qualitative research papers.

Methods
The OPEN study assessed the feasibility of a future randomised controlled trial on olanzapine in young people with anorexia nervosa in an open-label, one-armed feasibility study. In this study, we aimed to include 55 patients with anorexia nervosa or atypical anorexia nervosa aged 12–24 who gained < 2 kg within at least 1 month of treatment as usual. Time points for assessments were at baseline, 8 weeks, 16 weeks, and 6 or 12 months. We estimated recruitment, adherence and attrition rates and mean changes in body weight, body mass index and eating disorder psychopathology. In addition, we explored the views on and experiences with olanzapine treatment within a clinical trial setting using qualitative interviews with young people with anorexia nervosa, their families and clinicians.

Results
Fifty-two people were pre-screened, 35 were eligible and 20 participants were recruited and started olanzapine. Of these, 15 continued olanzapine for ≥ 16 weeks. Participants experienced, on average, a decrease in their eating disorder psychopathology, and body weight and body mass index increased during treatment with olanzapine as an adjunct to treatment as usual. Important themes derived from semi-structured qualitative interviews with young people and their parents were: moving away from the illness towards recovery, evaluating information on olanzapine, consent and trust in shared decision-making and the ambivalence around recovery. The main themes expressed by clinicians included: acknowledging the concerns of young people with anorexia nervosa and their families, prioritising person-centred care, the limited service capacity and strict study eligibility criteria.

Limitations
The study failed to meet the recruitment target and showed low adherence rates for treatment with olanzapine. Possible reasons for the recruitment difficulties and the low adherence rate include the high clinical workload of eating disorder services during and after the COVID-19 pandemic, the heterogeneity of eating disorder service setup across the country, and the reluctance of patients to agree to take olanzapine under the relatively restricted conditions of a clinical study.

Conclusions
A realistic time schedule for site-preparation, recruitment, treatment and follow-up, realistic recruitment targets and easy access to medical and laboratory examinations may improve the success of future feasibility studies and randomised controlled trials in this patient group.

Future work
The difficulties in conducting the OPEN study will inform the planning for future pharmacological and non-pharmacological studies in anorexia nervosa. Therefore, we developed a checklist with action points for the planning of pharmacological trials in eating disorders. Furthermore, novel pharmacological options such as typical and atypical psychedelic drugs (e.g. psilocybin and ketamine) might be more acceptable for people with anorexia nervosa as they do not have the side effect of immediate weight gain.

Publication Type:	Article
Additional Information:	Copyright © 2026 Filiz et al. This work was produced by Filiz et al. under the terms of a commissioning contract issued by the Secretary of State for Health and Social Care. This is an Open Access publication distributed under the terms of the Creative Commons Attribution CC BY 4.0 licence, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. See: https://creativecommons.org/licenses/by/4.0/. For attribution the title, original author(s), the publication source – NIHR Journals Library, and the DOI of the publication must be cited.
Subjects:	R Medicine > R Medicine (General) R Medicine > RM Therapeutics. Pharmacology
Departments:	School of Health & Medical Sciences School of Health & Medical Sciences > Department of Nursing & Midwifery
SWORD Depositor:	Symplectic Administrator

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