The goal of this clinical trial is to examine the feasibility and acceptability of a brief guided self-help wellbeing intervention for autistic adults accessing UK secondary mental health services. The study also aims to begin to evaluate whether use of the workbook is associated with any changes in wellbeing. The main questions it aims to answer are:

1. Is it feasible to recruit and retain autistic adults to participate in the study?
2. Do participants find the workbook acceptable and relevant?
3. Are there measurable improvements in wellbeing following workbook use?
4. What changes, if any, do participants recommend for future versions of the intervention?

Participants will:

• Take part in 4-6 sessions of 30-60 minutes using the guided self-help workbook with the support of a trained National Health Service support worker, assistant psychologist, or mental health professional
• Complete wellbeing questionnaires before, during, and after using the workbook
• Complete brief daily wellbeing ratings throughout the study
• Take part in a 1:1 semi-structured interview of up to an hour to discuss their experience of the workbook

Autism is a lifelong neurodevelopmental difference that affects how people communicate, experience the world, and relate to others. In the UK, more than 1% of people are estimated to be autistic, with rates of diagnosis rapidly increasing. Many autistic adults experience mental health challenges such as anxiety, depression, and suicidal thoughts. Some may experience 'autistic burnout', a state of deep exhaustion and loss of coping ability. These difficulties can result from long-term stress, 'masking' (hiding autistic traits to fit in), and lack of understanding or support.

In the UK National Health Service, post-diagnostic support for autistic adults is limited, often consisting only of information or signposting. While existing psychological therapies can help with anxiety and depression, they are not always designed with the needs of autistic people in mind. This highlights a clear need for preventative, accessible, and autism-specific wellbeing support, especially within the National Health Service, where demand is high and resources are limited.

This study aims to explore whether a new guided self-help wellbeing workbook designed specifically for autistic adults is feasible and acceptable, and to get an initial impression of its helpfulness in improving wellbeing. It focuses on helping people to understand autism and manage their energy levels using 'energy accounting' (Toudal & Attwood, 2024), and to plan for wellbeing using personalised strategies. The aim is to help autistic adults improve self-understanding, communicate their needs, and enhance wellbeing in everyday life.

The study will have three phases (baseline: a 1-2 week period prior to completing the workbook; intervention: a 4-6 week period during completion of the workbook; follow-up: a 3-4 week period following workbook completion). Participants will be asked to complete standardised questionnaires at the beginning and end of each phase. Brief daily wellbeing ratings will be collected throughout all three phases. Finally, an interview of up to an hour will be conducted with participants at the end of the follow-up phase.

There are six primary indicators which will be compared against pre-specified progression criteria. The primary outcomes are 1) ease of recruitment to the study; 2) participant retention in the intervention; 3) participant retention in the study; 4) intervention acceptability; 5) outcome measure completion; 6) whether there is a preliminary indicator of efficacy on the primary outcome measure (wellbeing). Progression criteria will be used to help decide whether the research should progress to more powered intervention studies in future.

Inclusion Criteria:

• A pre-existing diagnosis of autism OR on a waiting list for autism assessment OR self-identified as autistic and scoring above cut-off on the autism quotient (AQ-50) screening questionnaire.
• Aged 18 years or over and able to give informed consent to participate.
• Under the care of a community-based mental health team in Kent and Medway Mental Health NHS Trust and not due for discharge during the study period.
• Have already completed assessment processes (including risk assessment) during intake by the clinical team and a management plan is in place.
• The named clinician assesses that the individual is in sufficiently stable condition to participate in the study, and is likely to remain engaged in the intervention.
• Proficiency in reading and writing English.
• If on medication for mental health, the dose is stable (minimum of 3 months) with no planned changes during the study.

Exclusion Criteria:

• Presence of a moderate to severe learning disability that would limit independent engagement with self-help materials.
• Engaged in another psychological therapy or psychologically-informed intervention, or due to begin another during the study.
• Current acute mental health crisis or elevated risk to self/others requiring intensive intervention (assessed via clinical team judgement).
• Insufficient capacity to engage with the study protocol or complete measures (as determined by the care team).

Individual participant data will not be shared because the study involves extensive data collection from a small number of participants, which may increase the risk of participant identification.