The goal of this study is to deliver a definitive randomised controlled trial to measure the effectiveness and assess cost-effectiveness of a digital social intervention for patients with asthma, composed of promoting engagement with online peer support in a primary care consultation, followed by engagement with online peer support for 12 months. The main questions/objectives this study aims to answer/address are:

• Does promoting engagement with an online health community in primary care help people with troublesome asthma to experience fewer asthma symptoms?
• To assess cost-effectiveness of the intervention (including quality of life, well-being, use of healthcare services etc); stakeholder satisfaction (patients and healthcare professionals) with the intervention; fidelity of protocol delivery; context in which positive outcomes can be triggered.

Patients with troublesome asthma, from 50-70 UK general practices, who might consider seeking advice online will be identified through a short online survey. The survey will include an asthma control test (ACT) questionnaire, a question about the network of support they have with their asthma, whether they are members of another existing online health community and whether they would be interested in taking part in a research study involving engagement in an asthma online health community (if randomised to the intervention arm).

Patients meeting the eligibility criteria will be asked to attend a one-to-one consultation with a healthcare professional at their general practice, who will randomise them using a randomisation tool and subsequently deliver the intervention encouraging them to engage with the asthma online health community or provide usual primary care, respectively. Participants of the intervention arm will be given a username and password for the Asthma + Lung UK online health community and shown how to login to the online health community. Participants will be asked to complete an online questionnaire at this consultation and again 12 months later. The consultation should take 30-45 minutes and completing the data-collection questionnaire 12 months later should take around 10 minutes.

During the 12-month period after the consultation, patients will be phoned by members of the research team every 3 months to collect data through an ACT questionnaire as well as volume of asthma exacerbations and associated healthcare utiilisation (primary and secondary care attendances) within last 3 months. Monthly text messages will also be sent to participants in the intervention arm who have consented, reminding them to engage with the online health community. The final follow-up questionnaire will include questions about how well their asthma is controlled, anxiety and depression, taking their asthma medication, and quality of life. Subject to participants' consent, the investigators will also endeavour to extract data from healthcare records about asthma exacerbations and use of primary and secondary care health services during the 12-month follow-up period (for both control and intervention arm participants). This data will be obtained from 'Discovery' for practices in North-East London. 'Discovery' is a clinical partnership project in East London, run by the Clinical Effectiveness Group at Queen Mary University of London and setting out to link primary and secondary care records, by creating a single database. The Clinical Effectiveness Group extracts data in an anonymised format. For practices in other parts of the UK, NHS Digital will be used to obtain data from healthcare records, and respective protocols and policies will be followed.

Data on intervention arm participants' use of the Asthma + Lung UK OHC during the study period will be collected and analysed, subject to consent, including the amount of engagement (number of days, hours/day etc.), community/ies joined, number of logins, number of likes, and time spent on pages, as well as the content of any public posts made by participants (private messages sent on the OHC will not be accessed or analysed).

At the end of the 12-month follow-up period, one-to-one interviews will be carried out with approximately 25 of the participating patients and approximately 15 of the HCPs involved in the study. Exact numbers will be determined by the point of data saturation being reached, with further interviewees being recruited if necessary. A convenience sample of participants will be invited (by email/text/phone) to take part in this one-off interview, which will last around one hour. Interviews will be carried out by a member of the research team and take place remotely via an appropriate online platform (Zoom or Microsoft Teams). During the interview, participants will be asked a series of questions (from a pre-determined list) exploring their views about their involvement in the study. Interviews will be audio recorded (after securing participants' consent - relevant field in the consent form) for subsequent analysis.

Inclusion Criteria:

To participate in the study, participants will need to:

• Be adult asthma patients (aged 18 to 99) who have expressed their interest in digital social interventions in the recruitment survey.
• Report troublesome asthma (i.e. an ACT score of less than 20) in the recruitment survey).
• Be competent to consent for themselves, as determined by the healthcare professional delivering the consultation.

There are no specific criteria for selecting participants for the exit interviews (a convenience sample of patients and clinicians will be used and recruitment will continue until data saturation).

Exclusion Criteria:

• Patients who are already members of the Asthma + Lung UK online health community or other asthma online health communities/Facebook groups (i.e. general use of social media will not prevent participation).
• Palliative or end of life patients.
• Patients receiving institutional long-term care (receiving total care in residential homes or living in nursing homes).
• Patients considered unsuitable to take part in the study by their general practitioners/nurses.

There are no specific criteria for selecting participants for the exit interviews (a convenience sample of patients and clinicians will be used and recruitment will continue until data saturation).

Data from individual participants will not be shared. Participants will not be individually identifiable from any research outputs. 'Pseudonymisation of data' will be the policy for ensuring confidentiality. All participants will be coded, by allocating them unique participation codes. The association between participation codes and names will be contained on a Word/Excel document and will be stored on a password-protected computer at Queen Mary University of London. Any electronic documents or hard copies of data collected from participants will only be accessible to the research team. Only members of the research team will have access to associations between names and participation codes. Every attempt will be made to pool/aggregate or coarsely categorise potentially identifiable information in any dissemination of research findings.

Masking is not possible.