Descriptive data.

We included data on patients’ attendance at group sessions as well as demographic information and primary DSM-5 diagnosis that were collected during the trial. For professionals, the total number of sessions they delivered and drop-outs among MHPs were registered during the RCT. These data were used as background information for the interviews conducted.

Interviews and RE-AIM theoretical framework.

Data were collected via semi-structured interviews applying the RE-AIM framework for the evaluation of the implementation. This framework was also used for the design of the interview guide and topics [25,26]. The RE-AIM framework proposes a critical assessment of five dimensions regarding implementation: reach, efficacy, adoption, implementation and maintenance. These dimensions will be briefly explained here.

Reach. This dimension assesses to what extent the target population is reached and willing to participate. We evaluated how FACT teams approached the recruitment of patients and to what extent the intervention meets the FACT population’s needs. In line with this, we explored opportunities for improving access and appropriateness of the intervention to meet the needs of people with SMI.

Efficacy. In the context of this process evaluation, efficacy refers to the effect of the KISMET intervention on smoking (cessation), quit attempts, and awareness of one’s own smoking behaviour. We systematically questioned the three components of the intervention and their perceived effectiveness. Additionally, we investigated how carbon monoxide (CO) monitoring, which was part of regular study assessments, was utilised and perceived by patients and MHPs.

Adoption. This dimension refers to the settings and temporal circumstances of mental health organisations that were willing to implement the intervention. In our research, we explored how policies and culture regarding smoking within institutions might have created the conditions for FACT teams to be motivated to adopt the intervention. Moreover, we investigated how MHPs experienced the preparatory training, as well as their motivation and willingness to deliver the intervention.

Implementation. This dimension refers to MHPs’ fidelity to the original intervention protocol and identifies which adjustments to the protocol MHPs made. In addition to the interviews, we used the observations that the researchers (MK and LJ) made during the group sessions they joined to assess fidelity. This dimension also encompasses facilitators and challenges experienced by MHPs while implementing the intervention.

Maintenance. This dimension indicates the extent to which mental health care organisations or FACT teams intend to incorporate the intervention after the KISMET trial has ended.

A more detailed overview of the topics and corresponding interview questions can be found in Appendix II in S1 File.

On-site observations.

Complementary to the interviews with MHPs and patients we joined one group session and one peer support group meeting in nine out of 11 intervention teams. One FACT team decided against this as they expected a possibly negative impact on the group dynamics and the comfort of their patients. We collected information about the interaction between MHPs and patients, group dynamics, and proactivity and involvement of patients. We assessed fidelity to the KISMET intervention protocol regarding the extent to which the session adhered to the structure and content by scoring them ‘completely/ partly/ not at all implemented’. The most frequent and notable observations from our on-site observations were summarised. Observations were registered with a pre-defined form (Appendix III in S1 File).

Cognitive behavioural support group.

Patients described psychoeducation about tobacco addiction, health risks of smoking and (addictive) ingredients in a cigarette to be an engaging introduction as it was considered both a confrontation and an ‘eye opener’. Specifically, CBT-based exercises, such as registering which situations or emotions usually trigger the urge to smoke (more) yielded relevant insights. Patients acquired a deeper understanding of their underlying emotions that motivate smoking and could critically revise smoking as a routine response to negative emotions or stress. Likewise, MHPs corroborated the experiences shared by the patients and integrated them into setting new treatment goals.

“I enjoyed it very much; it’s a nice group of people. It was also great to work towards something positive together, towards a healthier lifestyle and its benefits. Not just talking about problems.” (MHP2)

Patients emphasized that addressing the interaction of smoking and (the severity of) their psychiatric symptoms was indispensable in the treatment of tobacco addiction. According to patients, more efforts should be devoted to the function of smoking for stress management, since experiencing distress was the most likely reason for relapse. At times, MHPs noted that it was challenging to deliver the sessions to a diverse group of people. Different levels of cognitive capacity and concentration lead to discrepancies in how much people could follow and engage in the group sessions. The experience of psychotic and, particularly, negative symptoms, as well as using antipsychotic medication, impeded group participation. MHPs described it as difficult to balance the amount of information and pace of conversation to make the group sessions stimulating and manageable for every participant.

Overall, patients experienced the group setting as enriching. The three months with weekly sessions was considered too short, however. Primarily because the process of preparing for a quit attempt took more time than expected. Most patients made a quit attempt towards the end of the three-month intensive phase. Consequently, decreasing the frequency of sessions at this point was not helpful as some people still needed weekly support. The preferred frequency of meetings also depended on patients’ current mental health status. For example, starting a smoking cessation trajectory parallel to other intensive psychological treatments, such as Eye Movement Desensitization and Reprocessing (EMDR), weekly meetings were too frequent.

Peer support group.

Both patients and MHPs described the concept of peer support as beneficial. Working with a (former) patient or MHP who has successfully quit smoking was considered helpful. Experts-by-experience who were interviewed recognised appreciation from patients upon sharing their experiences with nicotine withdrawal, relapse, health benefits after smoking cessation and stress management. Furthermore, sharing information and experiences regarding the use of medication for smoking cessation was valued by patients; it helped to diminish doubts and created more optimistic expectations towards medication use and its effectiveness. In the original implementation plan, peer support group meetings were scheduled weekly on the same day as the group sessions. However, patients found it exhausting to attend two consecutive hours of group sessions. Patients and MHPs suggested combining both groups into one session.

Pharmacological treatment.

Twenty-one patients (28.4%) participating in the KISMET intervention indicated that they received pharmacological treatment for smoking cessation at 12-month follow-up. Thirteen patients (17.5%) used NRT (nicotine patches, melt tablets and/or chewing gum). Eight patients (10.8%) used other pharmacological support, i.e., Cytisine, Bupropion, or Nortriptyline, whether in combination with NRT. Overall, patients reported minimal side effects and regarded NRT as highly effective in coping with withdrawal symptoms and severe cravings. By alleviating these symptoms, patients felt they were able to focus more on the psychological aspects of their tobacco addiction and cessation.

“It kind of gave me the feeling that half of the battle was already won, […] because the patches gave me some kind of peace, physically.” (P6)

Since Bupropion and Nortriptyline are antidepressants, psychiatrists did not prescribe them if other antidepressants were already prescribed or were generally advising against the use of medication for smoking cessation due to the potential side effects and interactions with antipsychotic medications. Complicated prescription procedures and the unavailability of psychiatrists hindered the accessibility and effective use of smoking cessation medication. Patients from some FACT teams complained about long waiting times for a consultation appointment and delays in the delivery of medication. These complications also influenced patients’ planning of their quit attempt, as well as their overall motivation and readiness to quit.

“Most of us were supposed to see a psychiatrist before the intervention started. Well, that wasn’t the case, and some people only got a consultation for medication after six months. [...] So it was a long wait and that eats away at your motivation.” (P9)

Carbon monoxide (CO) monitoring.

Even though not a part of the original intervention protocol, but part of the study assessments, CO monitoring was mentioned as a helpful tool by patients and MHPs.

“The CO measurement was always a confrontation with how much they smoked and what effect it has on their body. I think that it is a good and helpful method.” (MHP2)

During the group sessions, patients were motivated by the results of the CO monitoring. When their CO levels were low, indicating that they had smoked few or no cigarettes shortly before the measurement, patients felt encouraged by seeing the immediate results of their efforts. This boosted their motivation to remain abstinent or to further reduce their daily cigarette intake. On the other hand, when their CO levels were high, patients saw the monitoring as a confrontation.

“Sometimes my CO level was very low, which I was glad about. Other times it was that of an extremely heavy smoker. So, it was very confrontational, but good to do it and get back on track.” (P2)

Patient level.

Patients’ adherence to the group sessions was a crucial factor for a smooth implementation. In all FACT teams, patients noted their inconsistent attendance as well as that of others. Various reasons were given for inconsistent attendance, such as increased severity of psychiatric symptoms, low motivation, or other commitments such as psychotherapy. Patients who attended regularly described feeling left alone by other patients in the group who dropped out or were often absent. Accumulatively, the inconsistency in presence disrupted the overall flow of implementing the KISMET intervention as sessions were occasionally cancelled or held short, due to the absence of patients.

MHP level.

Twenty-six MHPs (out of 32) attended the KISMET training. Most MHPs expressed that they found the training a good preparation for implementing the intervention. There was variation in prior knowledge and skills regarding smoking cessation support, CBT and MI techniques. MHPs indicated that their preexisting knowledge and experience heightened their confidence in their ability to deliver the intervention, potentially leading to better implementation.

Professionals agreed that the KISMET handbook offered excellent guidance and instructions through detailed descriptions of the sessions’ content. MHPs appreciated the consistent structure of the handbook and noted that it elevated their confidence regarding the delivery of the intervention. This significantly contributed to treatment fidelity. Occasionally, professionals deviated from the protocol regarding the duration of the sessions or spread the content of one session over multiple sessions. Adjustments were made in response to patients’ needs, preferences and capacities. We observed nine group sessions in nine (out of 11) intervention teams. All teams adhered to the content of the session as protocolised in the handbook. The structure of the sessions as proposed in the handbook (1. check-in; 2. group discussion; 3. goal setting for the following weeks) was less complied with, as four FACT teams did not have a check-in in the beginning and did not finish the session with goal setting for the following weeks. Regarding peer support, most FACT teams could not implement regular meetings due to the unavailability of staff.

Professionals’ beliefs regarding patients’ autonomy were decisive in how they experienced their patients’ participation in the intervention. MHPs who attributed high autonomy to their patients reported less frustration about a stagnating process regarding smoking cessation or unsuccessful quit attempts. More specifically, these MHPs portrayed the process of quitting entirely owned by the patients themselves, while meeting the patients’ need for support.

“We try to encourage patients to look at the disadvantages of smoking and the advantages of quitting. But ultimately everyone remains responsible for their process. You must slow yourself down so that you don’t fall into the trap of pushing and pushing.” (MHP1)

This can benefit implementation as professionals hold more positive attitudes regarding the KISMET intervention. Some MHPs admitted to having pessimistic expectations regarding the chances to quit smoking of some individuals in this patient group.

Relationship MHP – patient.

Mutual trust to commit to the group sessions and the common goal of working towards smoking cessation was perceived as the fundament for a strong collaboration, according to MHPs.

Patients’ lack of compliance with the group sessions weakened the trust of MHPs in the chances for successful quitting. According to patients, this sometimes expressed itself in a vicious cycle of pessimistic expectations by MHPs and patients who perceived this lack of confidence and therefore complied even less. For patients, compliance by MHPs critically contributed to the feeling of being taken seriously. Extra efforts by the MHPs to do reminder calls or messages before the sessions were appreciated by patients. Irregularity or cancellations of group sessions demotivated patients and harmed the therapeutic alliance and was therefore an obstacle to implementation.

“At a certain point, I had the feeling that X and Y [MHPs] were not that motivated because group sessions were rescheduled or cancelled very often. And then I started to feel that in the other clients, too. […] I don’t think that anyone felt like they were being taken seriously anymore.” (P6)

FACT team level.

Patients and MHPs from FACT teams in which there was high regularity and consistency in the delivery of the intervention mainly assigned this to effective teamwork and communication within the entire FACT team. MHPs evaluated the implementation more positively when they thought that the collaboration with their colleagues was effective. Support from colleagues not directly involved in the implementation of KISMET included, for instance, following up with patients from their caseload who participated in the KISMET intervention and reporting back to their colleagues delivering it. However, it was also noted that communication with other team members was often difficult due to the way how FACT teams work, including frequent house visitations, limiting contact on location with colleagues. Moreover, a shortage in clinical staff and turnover were reported by the majority of MHPs making teamwork more challenging.

The shortage in staff and lack of collaboration was particularly noted among psychiatrists. Pharmacological treatment for smoking cessation depended on the cooperation between psychiatrists/ clinical nurse specialists (CNS) and MHPs delivering the group sessions. Consequently, disruptions in communication resulted in consultation appointments later than patients requested and little or no monitoring. In addition, many psychiatrists and CNSs had little experience with the prescription procedures, especially for NRT. In FACT teams that reported the least complications around implementing pharmacological treatment, consultation appointments were scheduled by default for every patient at the beginning of the intervention.

Organisational level.

Lastly, MHPs critically evaluated the implementation on an organisational level. Unanimously, more embedding is necessary to facilitate the implementation of the KISMET intervention. Professionals suggested that managers should take a more active role in the planning and organisation, for example, by ensuring that FACT teams are staffed sufficiently to carry the extra workload and compensate where needed. Moreover, to make it a higher priority among all FACT team professionals and to stimulate their proactivity with patients regarding smoking cessation.