Table 3 Overview of the MENTUPP ToC assumptions

1. The national culture is in favor of promoting mental wellbeing and talking about mental illness

Research has shown that the national culture of a country may have an impact on the beliefs, attitudes, coping strategies, and help-seeking behaviors of citizens [47]. We assume that a general attitude about mental health in a country will probably have an influence on how the MENTUPP intervention is used and that countries in which there is a more open attitude about mental illness will promote the acceptability of the intervention

2. The SME has sufficient resources

We assume that the participating SMEs have sufficient resources (time, financial resources, human capacity) all through the implementation period.Even if the availability of resources is discussed beforehand with the director of the SME during recruitment, SMEs often struggle with new financial constraints in order to survive and grow

3. The SME has an organizational culture that supports MENTUPP

We assume that SMEs who choose to participate in MENTUPP are to a certain degree interested in mental health promotion and preventing mental illness in employees and perceive it as useful

4. The SME has a current need for mental health promotion and prevention of mental illness

We assume that the MENTUPP intervention will be appreciated particularly by SMEs that strive to promote employees’ mental wellbeing and support employees with mental illness

5. Employees have internet access

Without internet access employees cannot make use of the internet-based MENTUPP intervention. We, therefore, assume that employees have access to the internet, a computer, and/or a mobile phone

6. Employees have proficiency in the language that is used by MENTUPP

The development of the intervention components takes into consideration that the language used has to be tailored to the language level of the participants. However, we assume that there is a possibility that not all the needs are met with respect to language proficiency

7. MENTUPP fits into the daily routine of employees

We assume that participants will use the MENTUPP Hub if it fits into their daily routines. It is recommended that, the MENTUPP Hub is mostly used during working hours. However, people occupied in SMEs often face lack of time due to multiple challenges that they have to handle

8. New employees are actively involved in the intervention

For MENTUPP to become sustainable, the SMEs have to systematically introduce new employees to the MENTUPP intervention and provide them access to the Hub

9. Implementation is disrupted as little as possible by unexpected events on a national or organizational level

We assume that the implementation of MENTUPP has the potential to be adapted to unexpected events and public health emergencies at national level (e.g., the COVID pandemic, a natural disaster, the loss of an influential person) or on the organizational level (e.g., a sudden change in management, the dismissal of a key employee, an impending bankruptcy)

10. MENTUPP is supported by mental health professionals independent from the project

For MENTUPP to be more effective, the existence of external mental health professionals supporting the intervention and providing the participants with additional help is required. We assume that the provision to refer to additional tailored mental health services and support as required will be promoted

11. Leaders’ decision making related to working environment is influenced by MENTUPP

We assume that MENTUPP will inspire leaders to follow work processes, policies, and structures in favor of mental health promotion in the workplace