Multicentre randomised controlled trial of the Norwegian health in work service for patients with common mental disorders or musculoskeletal disorders: the Norwegian Sickness Absence Clinic (NSAC) Efficacy Study.

Multicentre randomised controlled trial of the Norwegian health in work service for patients with common mental disorders or musculoskeletal disorders: the Norwegian Sickness Absence Clinic (NSAC) Efficacy Study - PMC Skip to main content An official website of the United States government Here's how you know Here's how you know Search Log in Primary site navigation Search Log in Search PMC Full-Text Archive Search in PMC Journal List User Guide As a library, NLM provides access to scientific literature. Inclusion in an NLM database does not imply endorsement of, or agreement with, the contents by NLM or the National Institutes of Health. Learn more: PMC Disclaimer | PMC Copyright Notice BMJ Open . 2026 May 28;16(5):e109083. doi: 10.1136/bmjopen-2025-109083 Multicentre randomised controlled trial of the Norwegian health in work service for patients with common mental disorders or musculoskeletal disorders: the Norwegian Sickness Absence Clinic (NSAC) Efficacy Study Nils Abel Prestegård Aars 1, 2, ✉ , Ingvild Bardal 1 , Christoffer Terjesen 3 , Bernt Ole Hansen 2 , Anders Jerven 4 , Kaja Irvung Kaspersen 5 , Øyvind Lyngedal 3 , Frank Hüttepohl 2 , Ingrid Johnsen 4 , Tina Olilla Uglebakken 5 , Beate Brinchmann 1 , Arnstein Mykletun 1, 6 Author information Article notes Copyright and License information 1 Centre for Work and Mental Health, Nordlands Hospital Trust, Bodø, Norway 2 HelseIArbeid, Nordlands Hospital Trust, Bodø, Norway 3 HelseIArbeid, University Hospital of Northern Norway, Tromsø, Norway 4 HelseIArbeid, Helgeland Hospital, Sandnessjøen, Norway 5 HelseIArbeid, Finnmark Hospital, Kirkenes, Norway 6 Department of Community Medicine, UiT The Arctic University of Norway, Tromsø, Norway Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise. None declared. ✉ Nils Abel Prestegård Aars; nils.abel.aars@nordlandssykehuset.no Received 2025 Aug 8; Accepted 2026 May 8; Collection date 2026. Copyright © Author(s) (or their employer(s)) 2026. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ Group. This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: https://creativecommons.org/licenses/by-nc/4.0/ . PMC Copyright notice PMCID: PMC13223649  PMID: 42209002 Abstract Introduction In many countries, a high or increasing rate of sickness absence is challenging the sustainability of present sickness absence benefit schemes. Most sickness absence is certified on the grounds of common mental disorders or musculoskeletal disorders, and substantial effort has been invested in developing interventions promoting return to work for these patients. In Norway, the Health in Work ((HelseIArbeid), HIA) clinics were established as outpatients’ services within the specialised healthcare system, with the aim of improving health and supporting return to work. The HIA service admits patients with low-to-moderate anxiety/depression and/or musculoskeletal disorders. In this protocol, we describe the naturalistic multicentre randomised controlled trial Norwegian Sickness Absence Clinic Efficacy study, which aims to determine the effect of HIA on work participation and health. Methods and analyses The HIA outpatient service is staffed by clinical psychologists, physiotherapists, medical specialists in physical medicine and rehabilitation and employment support supervisors from the Norwegian Labour and Welfare Administration. Patients admitted to HIA have access to multidisciplinary assessment and treatment. The trial recruits’ patients from five HIA outpatient clinics in Northern Norway. Patients are randomised in equal proportions to either (1) rapid HIA (assessment within 4 weeks), (2) delayed HIA (assessment within 10–14 weeks) or (3) active control, which consists of a monodisciplinary examination at HIA close to diagnosis-specific deadline for examination as suggested by guidelines (8–26 weeks). The trial commenced recruitment on 16 January 2023 and will recruit 2500 patients. The aim is to assess the effect of the HIA service, with the hypothesis that the HIA concept is superior to what resembles treatment as usual, in improving employment and preventing long-term welfare dependency. Secondary outcomes include self-reported symptoms of health problems. We also examine the effect the service has on other healthcare utilisation. To date, no research has been conducted to assess the efficacy of the HIA service. If proven efficacious, and if there is an economic case for this investment in tailored healthcare delivery, the policy implication may be implementation of the service at scale. If not, adaptations or investments into other viable paths of treatment may be considered. Ethics and dissemination The study is approved by the Regional Committee for Medical Research Ethics (REC North, #122770). Results from the study will be disseminated at national and international scientific conferences, to funders and participating outpatient clinics in seminars and in peer-reviewed scientific journals. Trial registration number NCT05310695 . Keywords: MENTAL HEALTH, REHABILITATION MEDICINE, Clinical Trial STRENGTHS AND LIMITATIONS OF THIS STUDY. A multicentre randomised controlled design was used to evaluate the HelseIArbeid (HIA) service under routine clinical conditions. The study is adequately powered to detect clinically meaningful effects according to diagnostic subgroups. Utilisation of national registry data ensures complete follow-up with respect to the primary outcomes. It is difficult to determine what constitutes treatment as usual in the absence of the HIA service, and the active control group may be considered both a limited or an expanded treatment between geographical regions. Introduction In most welfare states, an employee has the right to sickness absence (SA) with some degree of financial support. This net of social security is considered a public good with strong support in most countries in the Organisation for Economic Co-operation and Development. 1 2 A high and rising rate of SA challenges the sustainability of these policies, especially in the face of an ageing population. A major concern is that long-term sick leave may, for some, lead to the unnecessary exclusion from the labour market. Public policies aimed at reducing SA, welfare dependency, and increasing employment and return to work (RTW) are therefore of significant interest in many countries, including Norway. There are multiple political approaches to address this issue, including structural and systemic reforms, such as changes in welfare schemes and frameworks. 2 Another approach aimed at reducing SA is through tailored healthcare interventions. Common mental disorders (CMD) and musculoskeletal disorders (MSD) account for most SA and welfare dependency. 1 , 4 These conditions frequently co-occur, are highly prevalent, and demand considerable intervention resources. It is an assumption with strong face validity that medical care aimed at symptom reduction could help decrease or shorten the duration of absenteeism if the absence is attributed to health problems, but the evidence to support this is mixed. Treating the symptoms of mental or MSDs alone may be insufficient to reduce SA and promote employment, 5 and the evidence supporting a clinical approach to SA prevention and RTW through symptom relief remains limited. 6 , 8 Multiple factors can contribute to SA, 9 10 including work-related factors. 11 , 14 Multidisciplinary and work-oriented interventions have been promoted as promising strategies for RTW among patients with musculoskeletal pain 15 , 17 and mental disorders. Which work-related intervention or psychological interventions is the most efficacious with respect to RTW is not yet clear, 5 18 but Cognitive Behavioural Therapy based interventions have proven promising. 17 19 Further, it has been suggested that early interventions are preferable to prevent chronification of illness and prolonged absence from work, however, this approach was not proven efficacious in a systematic review and meta-analysis for persons with regional musculoskeletal pain. 6 Previous findings demonstrate that prolonged sick leave is a risk factor for a permanent exit from working life, 20 and an important challenge is to disrupt this process before sick leave progresses into permanent disability. In 2007, the Norwegian government introduced a funding scheme called ‘rapid return to work’ (Raskere tilbake) 21 based on the assumption that rapid treatment would reduce SA in the general population. The scheme was never formally evaluated for its effectiveness, and the healthcare sector’s component of it was restructured so that the allocated funds would be integrated into the regular patient services. The regional health authorities were tasked with establishing an outpatient service for patients with MSD or mild-to-moderate anxiety/depression. In Northern Norway, the concept ‘Health in work’ ((HelseIArbeid), HIA) was established to this end, which since has been implemented at several other hospitals in Norway but in slightly differing variants. The HIA service is a coordinated, multidisciplinary outpatient clinic with a work-focused treatment approach, where healthcare and welfare services (Norwegian Labour and Welfare Administration registry, NAV) are offered simultaneously. 22 The primary objective of HIA is to provide healthcare, reduce SA and support faster RTW or education through an integrated, work-oriented treatment approach. Whether this approach is efficacious is unknown and is therefore tested in a naturalistic multicentre randomised controlled trial (RCT) in the Norwegian Sickness Absence Clinic Efficacy (NSAC Efficacy) study. In this protocol, we present the NSAC Efficacy trial, and how we intend to evaluate the effect of HIA on RTW and symptom relief. Methods and analysis Aim The aim of this protocol is to describe the NSAC Efficacy RCT. The NSAC Efficacy trial aims to evaluate the effectiveness of the outpatient service HIA and was registered prospectively at ClinicalTrials.gov ( NCT05310695 ) on 3 March 2022. In this protocol, we describe the design, setting, intervention, comparisons, outcomes and known a priori strengths and limitations of the trial. Design The NSAC Efficacy is a naturalistic multicentre RCT, recruiting patients from five HIA outpatient clinics in Northern Norway. Patients are randomised in equal proportions to receive either (A) rapid HIA (delivered within 4 weeks after referral), (B) delayed HIA (delivered between 10 and 14 weeks after referral) or (C) active control: monodisciplinary examination at HIA close to diagnosis-specific deadline for examination as suggested by guidelines (8–26 weeks after referral, the majority at the end of this interval). In total the trial will recruit 2500 patients. Setting The NSAC Efficacy trial is led by the Centre for Work and Mental Health (CWMH), Nordland Hospital Trust, in Bodø, Norway. The HIA-service is a coordinated, multidisciplinary outpatient service, organised under the auspices of the specialist healthcare sector in Norway, which aims to (1) reduce sick leave and exclusion from work and (2) to provide necessary healthcare to patients with MSD or low- to moderate anxiety/depression. The HIA service still varies somewhat between the involved clinics, and a multicentre RCT design is therefore appropriate to increase the generalisability of findings. All five HIA clinics in Northern Norway participate in the NSAC Efficacy trial, and these are located in the cities Sandnessjøen (Helgeland Hospital), Bodø (Nordland Hospital), Tromsø & Harstad (University Hospital of Northern Norway) and Kirkenes (Finnmark Hospital). These clinics also took part in the NSAC Nudge trial between 2021 and January 2023. 23 In addition to the city in which they are located, each clinic serves smaller towns and cities in their vicinity. Northern Norway has a population of roughly 500 000 people, with the majority residing in urban areas. In Norway employees have the right to full salary compensation from the first day of SA and for up to 12 consecutive months of SA, after which the employee must work for 6 consecutive months to obtain rights for more SA. If the employee does not RTW after 12 months of SA, he/she is entitled to work assessment allowance (WAA) for up to 36 months. From the start of recruitment until its completion, receiving the standard HIA service will require informed consent to participate in the NSAC Efficacy trial. Patients that are eligible for admission to HIA but who do not consent to participate in the trial will receive a monodisciplinary assessment in line with what is provided to patients randomised to the active control group. Regardless of randomisation result, participants are not restricted from utilising other sources of healthcare during the study period. This means that patients may seek treatment in other parts of the healthcare system, both in the private and public sectors. In Norway, healthcare is free of charge, apart from a limited patient fee capped at a total of NOK 3278 (about 300 EUR) per calendar year of total expenses related to public sector healthcare and medication. Additionally, the government covers transport costs if the necessary treatment is unavailable nearby within the prescribed time frames for a given diagnosis. Recruitment of patients commenced on 16 January 2023 and concluded on 15 October 2025 when the required number of patients (n=2500) was reached. Characteristics of participants Patients are referred to HIA by general practitioners (GPs), by other health personnel with permission to refer to secondary care, or as secondary referrals from within the specialist healthcare sector. Eligibility for admission to the clinic is determined by a psychologist or a medical doctor. The service provided by HIA is primarily intended for patients with MSD or low-to-moderate anxiety/depression. Furthermore, the service is intended for patients holding a job or seeking employment/studies, meaning that recipients of long-term benefits such as disability pension (DP) or WAA are generally not admitted. The main criteria for not being eligible for assessment at HIA are being too healthy (the condition is considered to be manageable by services in primary healthcare), too sick (the appropriate treatment for the condition is considered to be other specialist treatment, e.g severe mental illness or concurrent untreated substance abuse), not relevant diagnosis or otherwise not considered being in the target group for the measure. What constitutes eligibility for specialist healthcare treatment is described in national, diagnosis-specific guidelines. Generally and historically, patients admitted to HIA on account of mental health disorders border on not being eligible for treatment in the specialist healthcare sector for lack of symptom severity. Accordingly, in the absence of the HIA service, treatment as usual would most likely be restricted to what the patients GP has to offer, including referrals to monodisciplinary treatment according to diagnosis or mental health treatment at the municipal level. For patients with MSD, many patients admitted to HIA would also qualify for treatment in specialised physical medicine and rehabilitation outpatient clinics. Patients considered eligible for treatment at the HIA clinics are also eligible for inclusion in the NSAC Efficacy trial but with some exceptions. First, patients which were included in the NSAC Nudge trial in 2022 23 may not be recruited to NSAC Efficacy within the first year of follow-up of that trial for the sake of outcome assessment in NSAC Nudge. Second, patients which are secondary referred from other departments/clinics within the hospital are not eligible for inclusion. Third, non-Norwegian or non-English speaking participants are not included since we were unable to provide validated and reliable questionnaires in other languages. Finally, patients which could not be reached by the research coordinator (RC) for information about the study are not included. Patients not included for these reasons may be offered ordinary treatment at HIA. Processes, recruitment, interventions and comparisons The HIA service has a work-focused treatment approach and is provided by multidisciplinary teams, with a basic staff model consisting of a medical specialist in physical medicine and rehabilitation, a psychologist, a physiotherapist and an employment support supervisor from NAV. According to local adaptations, other healthcare professions such as occupational therapists, welfare sector counsellors or mental health nurses may also be part of the staff model. The HIA service consists of different variants of monodisciplinary, multidisciplinary and interagency consultations simultaneously being delivered according to individual needs. Eligible patients are contacted via phone by an RC at the HIA clinic immediately after the patient’s referral has been considered. The RC informs the patient about the ongoing trial, and the implications of a consent- or non-consent in a neutral manner. If the patient accepts, the RC enters the patient’s email, personal identifier, deadline for assessment as determined by national guidelines, and which profession the patient should be assessed by if randomised to active control into a custom-built online survey platform developed by the CWMH in collaboration with the software provider Tivian (Tivian A/S, Oslo Norway) which also handles randomisation. If the patient has not been reached via phone within 14 days, the patient is provided an appointment within the capacity of the clinic, with treatment consisting of ordinary HIA. On registration, the software system issues an information letter to the patient via email. After 24 hours, the system issues a new email to the patient, this time containing a link to a questionnaire. On the first page, the patient is asked to provide his/her consent to participate in the trial. In the case of consent, the patient is immediately randomised to either of the three groups. The randomisation result is not relayed to the patient at this point. Lack of response to the consent form within 14 days is considered as non-consent. A copy of the consent page is available in online supplemental appendix 1 . In case of non-consent, the patient is forwarded to the same questionnaire as the participants, which the patient is asked to complete for clinical purposes. The questionnaire issued to patients prior to assessment at HIA was implemented and tested in a separate RCT, the NSAC Nudge. The details of NSAC Nudge are available in a separate protocol. 23 On consent, patients are randomised in equal proportions to one of three intervention arms: HIA-rapid (delivered within 4 weeks after referral). This group receives any service or clinical treatment which is deemed fit and within the scope of what HIA entails locally, and at the timepoint which is considered ideal according to the HIA concept. Delayed HIA (delivered between 10 and 14 weeks after referral). This group receives exactly the same as group A but delayed by 6–8 weeks. Active control consisting of a monodisciplinary examination at HIA close to diagnosis-specific deadline for examination as suggested by guidelines (8–26 weeks after referral, the majority at the end of this interval). 24 Patients randomised to this group receive a single 1–2-hour consultation with a single profession at HIA, that is either a physiotherapist, a psychologist or mental health nurse, or a medical specialist in physical medicine and rehabilitation. The intervention in the control group is provided by the same clinicians who also deliver the intervention to groups A and B. However, for the control group, they are instructed not to explore the work dimension and to focus solely on health. Both the psychologist/mental health nurse and the physiotherapist can consult the medical doctors on matters considered acute or beyond the scope of their professional competencies. For patients randomised to this group, an employment support supervisor from NAV may not be involved. The randomisation result is not conveyed directly to patients but is implicit by date of appointment in the appointment letter. Allocation is not concealed from clinicians but noted in the clinic schedule. Patients randomised to group C may be excluded from the trial post-randomisation if suicidal thoughts are expressed, or where the patient’s treating clinician finds it medically unsafe to not provide further treatment or follow-up. Each participating clinic has provided clear in-house protocols on what the control group intervention should consist of and adapted to local staffing and resources. Work packages The trial has three main work packages (WP1–3), each consisting of further subwork packages. WP1: effects In WP1a, we investigate the effect of HIA (groups A and B) on patients RTW outcomes compared with an active control treatment (group C). We will also compare groups A and B to examine if there is an effect of delivering the service very quickly. In WP1b, we will expand WP1a with stratified analyses per diagnostic group (mental disorders, MSD, both). WP1a and WP1b have follow-up data only in registries. In WP1c, we investigate the effect of HIA on patients’ self-report symptoms on follow-up surveys. We will also use future health service use according to patient registries as a proxy for health outcomes. In WP1d, we plan for a health economic assessment of the results in WP1a–c. The cost of the HIA service will be compared with the saving for society in terms of employment and welfare payments. This analysis will also consider how the service eventually influences the use of other health services. WP2: moderators and mediating factors In WP2a, we will investigate whether there are aspects of treatment, the patient or the patient’s situation that have impact on the effect of the HIA service on RTW or symptoms. WP2a is thus dependent on an effect in WP1. In WP2b, we investigate if the effect of the HIA service on occupational outcomes is mediated by improvement in health. In WP2c, we will examine how much of the improvement in functional level in terms of employment and benefit outcomes can be attributed to symptom relief. Finally, in WP2d, we will identify predictors of functional improvement. WP3: subgroup effects WP3 presupposes an effect in WP1. WP3 concerns investigating which patient group HIA works best for. In this WP, we seek to investigate whether the effect of HIA is influenced by motivation for work, work environment problems and barriers for RTW, as well as the rate of sick leave (100% sick leave, graded sick leave, no sick leave). Data sources The trial has five sources of data to answer the research questions. Patient questionnaire at baseline The questionnaire covers musculoskeletal problems, mental health and other health-related issues (such as alcohol consumption, medication and physical activity), as well as working conditions (including social support, work/family conflict and bullying), barriers for RTW, labour market affiliation, health-related quality of life and expectations for treatment. In an effort to reflect that the control condition entails less work focus, patients randomised to group C are not issued the questionnaires on work, motivation for work or barriers for RTW. Most of the questions have been validated, but some are developed for purpose of this specific trial. In an effort to reduce the number of questions posed to each patient, the questionnaire used index questions which have proven psychometric properties in terms of factor loading or similar, meaning that if a problem on a specific topic is not indicated, the patient will not be presented further questions on this matter. The consequence is that not all questions will be posed to all patients, and as a result many variables will have substantial missing data. A complete list of all the questions included in the baseline questionnaire is available in online supplemental appendix 2 . Clinician questionnaire completed after each consultation After each consultation the patient’s clinician completes a clinician questionnaire. This questionnaire is meant to capture the details of topics covered during assessment, as well as any specific procedures or interventions provided. The clinician also registers whether any other professions were consulted or involved as part of assessment, the duration of the consultation and any recommendations for treatment or follow-up assessment in either primary or specialist healthcare. A complete list of questions included in the clinician survey is available in online supplemental appendix 3 . Follow-up surveys Patients are issued the same questionnaire as provided at baseline 6 and 12 months postbaseline survey. The Norwegian Neck and Back Registry The Norwegian Neck and Back Registry (NNRR) is a national medical quality registry which includes patients with neck and back problems who are treated at multidisciplinary physical medicine outpatient clinics in Norwegian hospitals, of which HIA is a part. There is substantial overlap between the data collected by NNRR and in the NSAC Efficacy. To avoid posing the same questions twice to patients included in both NSAC Efficacy and NNRR, identical questions are provided to NSAC Efficacy from NNRR retrospectively rather than being collected twice. National registries In Norway, data from national registries are available to researchers for scientific purposes upon application. In the NSAC Efficacy, all patients consent to the collected data being linked to their data from such national registries. This ensures complete follow-up for key outcomes such as benefits or SA. The relevant registries include the Norwegian National Patient Registry, the Norwegian Control and Payment of Health Reimbursement and the NAV. Outcomes Because of the Norwegian legislation concerning rights to SA and salary compensation, any outcome involving RTW is influenced by length of SA prior to admission. The primary outcomes are functional recovery over short- and long term. This is operationalised as (1) employment during first 365 days post baseline survey, based on registry data and self-report, (2) SA during first 365 days post baseline survey, based on registry data and self-report, (3) application for health-related rehabilitation benefits during first 365 days post baseline survey, based on registry data and self-report, (4) employment during 5 and 10-year period post baseline survey, all based on registry data, (5) SA during 5 and 10-year period post baseline survey, all based on registry data, (6) health-related rehabilitation benefits during 5 and 10-year period post baseline survey, all based on registry data and (7) disability benefits during 5 and 10-year period post baseline survey, all based on registry data. The secondary outcomes concern changes in self-reported symptoms between baseline (t0) and 6-month follow-up (t1), and between t0 and 12-month follow-up (t2). A complete overview of all secondary outcomes is available at ClinicalTrials.gov and in online supplemental appendix 4 . Other outcome measures include changes in self-reported work environment, health-related quality of life, barriers for RTW, motivation for work and other factors surveyed between baseline and both follow-ups. A complete overview of all other outcomes is available at ClinicalTrials.gov and in online supplemental appendix 5 . Statistical analyses and power calculation We will use descriptive statistics for patient characteristics. The effect of the RCT on work outcomes and welfare dependency will be observed in registry data from NAV, operationalised as cumulative number of days on DP, WAA, FSA and GSA in the follow-up period following recruitment for each individual. The effect on work outcomes will be determined by testing for differences between randomisation arms using regression models. Specifically, we intend to use linear regression for metric outcomes (such as days on SA during 1-year follow-up) and logistic regression for dichotomous outcomes (such as working y/n at 1-year follow-up). For long-term outcomes, including health-related benefits during 5 and 10-year follow-up, analyses will be conducted using a longitudinal approach. Continuous outcomes, such as accumulated days of SA or employment over the follow-up period, will be analysed using linear regression models, whereas time-to-event outcomes, such as transition to work, WAA or DP, will be analysed using survival analysis methods. To account for clustering of patients within clinics, all regression models will incorporate a multilevel structure with clinic included as a random effect. The choice of statistical analyses will also depend on whether model assumptions are met, including the distribution of the data. In the presence of non-normal or skewed outcomes, appropriate transformations or alternative modelling approaches will be considered. WP2 involves secondary analysis of WP1, investigating whether the HIA effect depends on the place of treatment (five clinics), diagnosis (musculoskeletal, mental disorder, both), patient health (continuous variable from sick to healthy based on scales) and work situation. This will be tested with interaction analyses in regression models. We postulate effect moderation by patient characteristics, including the patients’ beliefs and wishes for RTW versus benefits, gender, satisfaction with current work and whether the patient believes their employer would like them back. Moderation will be assessed by including interaction terms between treatment allocation and candidate moderators. We also postulate no interaction for symptom severity at baseline. In addition, exploratory analyses for effect moderation beyond these predefined variables will be conducted. We will also explore effect moderation by characteristics of the services provided, such as number of outpatient visits to HIA, number of professions involved and type of profession involved, without a priori hypotheses regarding direction of effect. In WP3, we will use interaction analyses to investigate which patients have the best effect of HIA. This builds on WP HN-2a, concerning power modification for main diagnosis, site of treatment and disease burden. The purpose of mediation analyses is to explore potential causal pathways for RTW. All secondary and other outcomes will be considered as potential mediators. First, we will assess the effect of the HIA service on these outcomes; factors not influenced by randomisation will not be considered part of the causal pathway. Second, factors influenced by randomisation will be examined as potential mechanisms and further explored using structural equation modelling, allowing estimation of indirect effects on RTW. Interaction and mediation analyses will primarily be interpreted in light of the presence and magnitude of the main effect of randomisation on RTW. Furthermore, these analyses will require sufficient response rates in follow-up surveys. Power calculations were performed for main outcome measures and for the stratified analyses for patient groups defined by condition (mental vs musculoskeletal treatment, defined by the profession acting as main clinician during the treatment) and also work status (full-time work, full-time SA and combination of the two). The trial needs to recruit 2500 patients total in 3 equally sized groups to be adequately powered to detect a difference in effect size (Cohen’s D) of 0.2, given a beta of 0.1 and alpha of 0.05. Methodological considerations The NSAC Efficacy trial has a bold ambition of evaluating the effectiveness of a new outpatient service targeting patients suffering from mild-to-moderate CMD or MSD on work outcomes and symptom relief. The outpatient service ‘Health in Work’ is implemented nationally in Norway, with substantial endorsement and support from the government, the labour unions and the business organisations through the three-party inclusive work–life agreement. While the principles underlying the service are relatively consistent across different clinics and regions, there is still variation in approach and organisation of the service. In the northern region of Norway, the clinics have implemented this approach through coordinated collaboration and a relatively uniform professional framework. The results of this trial will inform service development and impact the eventual scale-up of HIA. Furthermore, the content and design may be implemented with adaptations internationally. Conversely, if the results do not indicate an effect in favour of the multidisciplinary and rapid HIA model, the search for new strategies to deter increasing rates of SA will have to continue. In the following, we discuss some aspects of the HIA service, the trial design and other factors which may exert an influence on the results of the trial. First, in the NSAC Efficacy trial, the assessment provided to the active control group is not identical to treatment as usual. For patients with MSD, the assessment provided may be less comprehensive than the ordinary treatment offered in a physical medicine and rehabilitation outpatient clinic. The assessment provided to patients with low-to-moderate anxiety/depression is in most cases probably more comprehensive than what would be the case in the absence of HIA as these patients generally are not considered eligible for specialised healthcare services. The implication is that, depending on cause for referral, a nil-finding may be induced if the control condition in practice is more comprehensive than the true treatment as usual (TAU), and conversely, if proven efficacious, that the true effect of HIA compared with TAU may be larger than what the trial detects. This issue is however not possible to avoid, as patients are assessed for admission to the specialist healthcare sector prior to randomisation, and once found eligible, the hospitals are legally bound to provide a treatment in line with national guidelines and within a predefined deadline. 24 Second, the active control treatment and the HIA service is delivered by the same personnel, which entails a risk of spillover, in favour of the nil hypothesis. Moreover, as clinicians deliver both conditions, it cannot be assumed that full clinical equipoise is maintained, as providers may hold preferences towards the care they routinely deliver. 25 Such preferences may influence delivery and introduce performance bias, potentially attenuating between-group differences. Third, as with any trial, the NSAC Efficacy study could expect a selection in which patient groups that provide consent to participate in the study, but this is difficult to investigate empirically as the non-consenters do not provide data to the project. The trial also has a limitation in how patients are recruited, as it involves contacting patients by phone to obtain email and inform about the study. Non-responders likely differ non-randomly on important characteristics from responders. The implication is that the NSAC Efficacy trial may recruit from a non-random HIA patient base, in which case the RTW prognosis may be slightly different from those included, regardless of treatment and randomisation arm, potentially diluting the difference detected. Fourth, we expect that a higher number of patients randomised to group C may retract their consent to participation, than among patients randomised to groups A or B. Furthermore, given that there are no trial-imposed limits to treatment and follow-up for patients randomised to groups A or B, we do not expect cases where the patient’s clinician requests the patient be exempted from trial participation for these two groups. This is more likely to occur for patients randomised to group C, and then for patients in the more severe end of symptom spectrum, potentially inducing a difference in symptom burden between randomisation groups. The extent of this is presently unknown, but future publications from this trial will include flowcharts of recruitment and cases of withdrawn consent. Fifth, since the trial is a multicentre RCT of an intervention which varies between clinics and clinicians according to preferences and experience, the intervention is less uniform than in, for instance, an RCT of a more standardised procedure or drug. The five HIA outpatient clinics are organised somewhat differently and have slightly different clinical approaches, assessments and treatment for the patients, as well as somewhat different practices regarding coding and tariffs. This reflects the naturalistic setting of the trial but also means that less is known of what constitutes the most effective component of the service and means that, for instance, healthcare utilisation between randomisation groups must also take into account which clinic the patient was admitted to. Finally, although HIA has a defined target group, some patients will have long-term health complaints and symptoms, and it is not certain that the HIA service is equally useful for chronic and more debilitating conditions. The patient group may vary between the different clinics in Northern Norway, and outcomes may be affected by other available resources locally or geographical constraints, which may affect the results of the study. Patient and public involvement The study was developed in close collaboration with the participating outpatient clinics. Representatives from the clinics gave crucial feedback on the design, the control group and ethical considerations prior to the study commencing. The CWMH has an ongoing collaboration with lived experience personnel which are consulted throughout the research process. Ethics and dissemination This study was approved by the Regional Medical Research Ethics Committee (REC North), approval id #122770. All participants in the trial have provided consent to participate in the trial, and a copy of the consent page is available in online supplemental appendix 1 . In addition to assessment of the efficacy of the HIA service, the data collected in the trial will be used for secondary purposes, including cross-sectional and longitudinal associations. In terms of adverse events, patients randomised to group C may be excluded from the trial post-randomisation if suicidal thoughts are expressed, or where the patient’s treating clinician finds it medically unsafe to not provide further treatment or follow-up. The trial does not impose limits on patients’ use of other healthcare resources, and as such, the risk of serious adverse events is considered low. All data in the trial will be stored in secure servers at Nordland Hospital and/or in TSD. The TSD service (short for ‘Service for Sensitive Data’) is tailored to store and process sensitive information in accordance with Norway’s ‘Personal Data Act’ and ‘Health Research Act’.’ Developed and operated by the University of Oslo’s IT Department, TSD supports research projects conducted at Norwegian public institutions. Within a highly secure environment, TSD offers access to virtual servers, storage solutions, backup systems, databases and high-performance computing resources. Additionally, TSD includes a wide range of software tools for data analysis and management. A limited number of project personnel will have access to the raw data, which will be cleaned and linked to registry data before being made available for analysis by other designated project members. The study will be carried out in full compliance with GDPR regulations. The data that support the findings of the study will be available from Nordland Hospital, but restrictions apply to the availability of these data and so will not be made publicly available. The results of the NSAC Efficacy will be published in scientific journals and authored in accordance with the principles of the Vancouver guidelines. In addition to dissemination to the scientific community at congresses and seminars, the findings will also be presented to and discussed with users and clinicians from the participating outpatient clinics, as well as to the funding body and through media outlets. Supplementary material online supplemental file 1 bmjopen-16-5-s001.docx (66.5KB, docx) DOI: 10.1136/bmjopen-2025-109083 online supplemental file 2 bmjopen-16-5-s002.docx (31.5KB, docx) DOI: 10.1136/bmjopen-2025-109083 online supplemental file 3 bmjopen-16-5-s003.docx (21.1KB, docx) DOI: 10.1136/bmjopen-2025-109083 online supplemental file 4 bmjopen-16-5-s004.docx (16.5KB, docx) DOI: 10.1136/bmjopen-2025-109083 online supplemental file 5 bmjopen-16-5-s005.docx (17.4KB, docx) DOI: 10.1136/bmjopen-2025-109083 Acknowledgements The authors are grateful for the cooperation and commitment from the staff at all participating clinics and for their role in the study. We also express our gratitude to all patients participating in the trial and to Helse Nord for funding this important research. Finally, we are especially grateful to Franz Hintringer and his role in the establishment of HIA and this trial. Helse Nord RHF has no role in the design, analyses, interpretation of results or dissemination of the trial’s findings. Footnotes Funding: The study described in this protocol is funded by the Regional Health Authority in Northern Norway (Helse Nord RHF) as commissioned research, grant number #2019/1168-XX. Prepublication history and additional supplemental material for this paper are available online. To view these files, please visit the journal online ( https://doi.org/10.1136/bmjopen-2025-109083 ). Provenance and peer review: Not commissioned; externally peer reviewed. Patient consent for publication: Not applicable. Patient and public involvement: Patients and/or the public were involved in the design, or conduct, or reporting, or dissemination plans of this research. Refer to the Methods section for further details. References 1. Hemmings P, Prinz C. Sickness and disability systems: comparing outcomes and policies in Norway with those in Sweden, the Netherlands and Switzerland. 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Supplementary Materials online supplemental file 1 bmjopen-16-5-s001.docx (66.5KB, docx) DOI: 10.1136/bmjopen-2025-109083 online supplemental file 2 bmjopen-16-5-s002.docx (31.5KB, docx) DOI: 10.1136/bmjopen-2025-109083 online supplemental file 3 bmjopen-16-5-s003.docx (21.1KB, docx) DOI: 10.1136/bmjopen-2025-109083 online supplemental file 4 bmjopen-16-5-s004.docx (16.5KB, docx) DOI: 10.1136/bmjopen-2025-109083 online supplemental file 5 bmjopen-16-5-s005.docx (17.4KB, docx) DOI: 10.1136/bmjopen-2025-109083 Articles from BMJ Open are provided here courtesy of BMJ Publishing Group ACTIONS View on publisher site PDF (320.2 KB) Cite Collections Permalink RESOURCES Similar articles Cited by other articles Links to NCBI Databases Follow NCBI NCBI on X (formerly known as Twitter) NCBI on Facebook NCBI on LinkedIn NCBI on GitHub NCBI RSS feed Connect with NLM NLM on X (formerly known as Twitter) NLM on Facebook NLM on YouTube National Library of Medicine 8600 Rockville Pike Bethesda, MD 20894 Web Policies FOIA HHS Vulnerability Disclosure Help Accessibility Careers NLM NIH HHS USA.gov Back to Top

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