Data collection for the present qualitative study took place between April and October of 2025. The RCT procedures are summarized briefly to provide contextual background for the qualitative follow-up study, which constitutes the primary focus of the present study. In the RCTs, interested individuals were initially contacted for a telephone screening interview to assess eligibility (t₋₁). Eligible participants were then invited to the Psychotherapeutic Outpatient Center of the University of Siegen, where written informed consent was obtained and baseline assessments were conducted as part of a comprehensive diagnostic session (t_₀). Following baseline assessment, participants were randomly assigned to either the experimental or a waitlist control condition. Participants in the experimental condition received a manual-based, 6-session smoking cessation intervention over a 3-week period, complemented by access to a smartphone-based self-help application. Postintervention assessments were conducted after treatment completion (t_₁), with follow-up assessments at 6 weeks (t_₂) and 6 months (t_₃). Participants enrolled in the second RCT continued their ongoing outpatient psychotherapy throughout the study period.

The intervention in the experimental group consisted of a manual-based, 6-step smoking cessation program that was adapted from a continuously evaluated tobacco cessation program in Germany, developed by the Smoking Cessation Working Group (Arbeitskreis Tabakentwöhnung) at the University Hospital for Psychiatry and Psychotherapy in Tübingen. The program, outlined in the manual by Batra and Buchkremer [38,39], is grounded in principles of cognitive behavioral therapy (CBT) and can be delivered in both group and individual settings. In the present study, the treatment was implemented individually. Over the course of 6 structured sessions, participants were guided through preparation and initiation of smoking cessation, the development of strategies to maintain abstinence, and relapse prevention techniques. At each session, carbon monoxide (CO) levels in exhaled breath were measured as part of the intervention using the Smokerlyzer. The sessions were organized into 3 phases (preparation, cessation, and maintenance), each addressing specific cognitive and behavioral aspects of quitting. Personalized recommendations were provided to tailor the treatment to each participant’s smoking history and psychological needs. In this research project, the original program was intensified to meet the needs of smokers with mental disorders by increasing the frequency of sessions and integrating a digital self-help component. Whereas the initial program was designed with weekly sessions, the intensified version comprised 2 sessions per week, resulting in a total intervention duration of 3 weeks. The digital self-help component consisted of access to the digital health application NichtraucherHelden (Sanero Medical GmbH). This CBT-based application comprises 8 interactive modules addressing psychoeducation, motivational enhancement, coping strategies, behavioral exercises, and relapse prevention. The application was designed to complement the face-to-face intervention by facilitating the consolidation of skills between sessions. A recent nationwide, multicenter RCT demonstrated the feasibility and efficacy of this guideline-based smoking cessation app, with approximately doubled 7-day point prevalence abstinence rates compared with a minimal-intervention control condition (20.2% vs 10.5%), which consisted of a brief 3-minute advice session [44].

The qualitative follow-up study drew on the RCT samples outlined above. All participants who had completed the smoking cessation intervention in the treatment arms of the 2 RCTs and whose 6-month follow-up appointments fell within the interview data-collection period were contacted by telephone and invited to participate in the face-to-face interviews, which were conducted in a 1:1 setting in the Psychotherapeutic Outpatient Center of the University of Siegen without any other individuals present. The target sample size was informed by methodological recommendations for qualitative interview studies, which suggest that 6‐12 participants are sufficient to obtain in-depth insights [45]. Consistent with Braun and Clarke’s [46] recommendations regarding sample size rationales in reflexive thematic analysis, sample adequacy was evaluated in terms of the depth, richness, and internal coherence of the dataset as a whole, reflecting our understanding that in a constructionist analytic approach themes are researcher constructions rather than entities residing in the data. It was nonetheless noted during analysis that later transcripts contributed progressively fewer new codes relative to earlier ones, which was taken as an empirical indication of sufficient dataset breadth for addressing the study’s research questions, without implying that the analytic construction of themes was complete or exhaustive. Eleven participants consented to participate and were included in the present analyses, while 6 participants declined participation in the interviews. The qualitative interviews were conducted in German by JB, a trained clinical psychologist, 6 months after completion of the smoking cessation intervention (t_₃). Interview duration ranged from 8 to 26 minutes (mean 17.27, SD 5.76 minutes). The interviews commenced with the interviewer posing the open-ended question: “How did you perceive the smoking cessation treatment in general?” This inquiry enabled participants to expound on their experience with the smoking cessation treatment in a free and spontaneous manner. Subsequent to the initial open-ended question, a semistructured interview procedure, adapted from the CCI [40], was carried out. The original CCI was developed to explore patient perspectives on psychotherapy, with a focus on perceived facilitators and barriers to change, attribution of experienced changes, and perceived missing elements in treatment. The interview guide is provided in Multimedia Appendix 1. For the present study, the interview guide was adapted to ensure relevance to smoking cessation while preserving its inductive character. Specifically, questions were phrased in an open-ended manner and tailored to address experiences with the smoking cessation treatment, study participation, and perceived psychological and social consequences of smoking cessation, without prespecifying response options or hypotheses. Hence, although the interview guide provided a loose structure by delineating broad thematic areas, the interview approach remained intentionally open and exploratory. Participants were encouraged to elaborate freely, determine the order and emphasis of topics, and introduce new themes beyond the predefined prompts.

All interviews were audio-recorded and transcribed verbatim using the automatic transcription function of f4x. Transcripts were subsequently reviewed by the authors to ensure accuracy.

Participants reported varying degrees of cessation success. Several participants described successful cessation even under conditions of substantial psychological distress or long-standing smoking histories:

Beyond sustained cessation, several accounts highlighted the nonlinear nature of behavior change, describing initial success followed by relapse, or difficulties maintaining reduced consumption over time:

Across these outcome patterns, participants frequently reported reductions in craving and increased awareness of situational smoking cues, indicating enhanced self-monitoring. Two participants described increased smoking, which was attributed primarily to changes in nicotine delivery methods, rather than a perceived failure of cessation efforts:

Changes in smoking behavior were closely linked to perceived alterations in mental well-being. For instance, participants frequently reported increases in positive affect, energy, and overall mood following abstinence or reduced smoking. These psychological improvements were predominantly attributed to experiences of mastery and self-efficacy:

Other participants ascribed psychological changes to improved stress regulation through newly acquired coping strategies, such as relaxation techniques, which were also incorporated into the cessation treatment:

Social validation further reinforced positive psychological outcomes:

Participants also described significant psychological strain during early abstinence:

However, these adverse experiences were predominantly framed as temporally bound. Even when withdrawal symptoms persisted beyond the anticipated 2-week period, participants described them as a necessary transitional phase preceding improvement.

Moreover, similar to withdrawal-related distress, negative affect following relapse was also perceived as transient:

Beyond changes in smoking behavior and mental well-being, participants described a range of personal and social consequences following cessation or reduction that shaped their ongoing motivation and capacity to maintain abstinence. These consequences were not experienced as neutral outcomes but as contextual factors that either reinforced or complicated sustained engagement with the cessation process. Gains in physical health, time, and financial resources were frequently described as tangible reinforcers of continued abstinence:

Conversely, participants reported social losses associated with reduced smoking. In some cases, individuals described consciously distancing themselves from smoking-related social contexts to protect their cessation efforts:

Such distancing was perceived differently, with participants reporting positive and negative experiences:

This ambivalence was especially pronounced in close relationships. One participant described reduced contact with a family member in the absence of shared smoking moments:

In sum, participants reported heterogeneous outcomes of the smoking cessation treatment within this overarching theme. While many described sustained improvements in smoking behavior and mental well-being, others experienced temporary declines in mental well-being due to withdrawal or relapse. Importantly, personal and social consequences of cessation emerged not merely as peripheral outcomes but as contextual factors shaping ongoing motivation and the capacity to maintain abstinence, underscoring the need for interventions that explicitly address the social embeddedness of smoking and support individuals in navigating the personal costs of cessation.

When describing facilitators and barriers to smoking cessation, participants frequently referred to the affect-regulatory, rewarding (“…that it’s such a pleasant moment for me in the evening, a bit like a reward” [Participant 3, position 14]), and instrumental functions smoking served in their everyday lives. Additionally, smoking embedded in habitual routines and automatic behaviors was a prominent barrier:

However, participants also reported that identifying and implementing functional substitutes facilitated smoking reduction or cessation:

Addressing habitual aspects of smoking by modifying environmental cues also emerged as a facilitative strategy to disrupt automatic smoking patterns:

However, some participants reported anxiety regarding the loss of smoking as a primary emotion regulation strategy, fearing that some new coping strategies might also turn into maladaptive behaviors:

Another central component frequently cited as a particularly important factor in participants’ smoking cessation trajectories was motivation, which was described as a dynamic and context-sensitive process. At treatment entry, participants retrospectively described varying levels of motivation, ranging from strong readiness to quit smoking to considerable difficulties engaging with the cessation process. Furthermore, participants frequently articulated the belief that intrinsic motivation and readiness to change were essential for cessation success (“It’s just that you can’t convince someone to stop if they don’t really want to” [Participant 3, position 28]). Importantly, motivation was described as malleable over the course of the treatment. Participants reported increases in intrinsic motivation due to the motivation analysis conducted in the second session, which was described as strengthening deliberate and autonomous decision-making:

Beyond formal treatment components, sustained abstinence itself was described as intrinsically motivating:

Information regarding the anticipated mental health benefits of smoking cessation, as well as experiencing them, was also reported as particularly encouraging:

Despite sustained or increasing motivation during the active treatment phase, many participants reported motivational fluctuations following the end of the structured cessation sessions due to the perceived loss of interpersonal accountability and support:

However, despite fluctuations in motivation following treatment completion, a long-term intention to quit often remained (“I still have that goal, of course” [Participant 11, position 6]).

Participants frequently emphasized the role of their social networks and immediate contexts, which both facilitated and impeded cessation success. In particular, several participants identified their smoking-normative social environment as a significant barrier to cessation:

These impediments were often attributed to concrete social processes, such as the presence of situational cues, which reinforced smoking or experiencing social pressure to accompany smoking peers to designated smoking areas:

Beyond direct social pressure, smoking was also perceived as fulfilling distinct social functions that reinforced cessation barriers. Participants described smoking breaks as structured social intervals that facilitated interaction and provided temporal orientation within social settings:

Notably, despite describing their smoking-heavy environments as challenging, some participants simultaneously reported receiving encouragement from smoking individuals for their cessation attempts:

In addition, participants attributed a substantial portion of their cessation success to supportive social networks, as encouragement and understanding were described as critical resources, particularly during high-risk situations:

Lastly, participants identified the disclosure of their cessation attempt to their social network as a facilitating factor. Although initially perceived as pressure-inducing, disclosure was retrospectively framed as increasing accountability and commitment:

Lastly, participants expressed heterogeneous perceptions regarding the appropriateness of the smoking cessation treatment for individuals with comorbid mental disorders. Some participants considered the intervention broadly suitable (“I think it’s suitable for anyone who wants to quit but can’t manage it” [Participant 10, position 51]). In contrast, a subset of participants expressed skepticism regarding its applicability, citing high effort, potential exacerbation of symptoms, or interference with ongoing therapy:

Skepticism was occasionally reinforced by perceived professional caution, with participants referencing health care providers’ reluctance to recommend cessation under high-stress conditions:

Notably, participants’ concerns contrasted with their own reported outcomes: despite skepticism about the treatment’s suitability for smokers with mental disorders, the same individuals generally described beneficial mental health effects and only short-lived negative consequences following cessation.

Overall, participants identified multiple facilitators and barriers to cessation, including the specific functions and automaticity of smoking, motivation, social networks, contextual influences, and treatment suitability for those with comorbid mental disorders. Taken together, these accounts suggest that cessation processes are closely intertwined with how participants experience and make use of the support provided during treatment, as well as how this support fits with their individual needs and circumstances.

Participants generally expressed favorable perceptions of the manual-based smoking cessation treatment, highlighting its structured modules, practical strategies, and the focus on alternative behaviors to replace smoking:

Similarly, preparation for high-risk situations was also described as beneficial, as participants were provided with concrete strategies for managing acute craving:

Conversely, the applied CO-measure elicited both motivational effects (“[…] seeing a lower [CO] number can definitely motivate you” [Participant 8, position 29]), as well as a feeling of being controlled:

Beyond the perceptions regarding specific modules and components of the cessation treatment, participants also delineated factors they perceived as beneficial in general. For instance, the broader psychotherapeutic context of the intervention was frequently cited as a key contributor to its efficacy:

Additionally, regular, structured appointments were perceived as reinforcing commitment, in part due to the motivational influence of accountability within the therapeutic relationship.

As study participation additionally involved the prescription of an application designed to facilitate smoking cessation, participants offered a range of comments pertaining to this application. Participants’ engagement with the application varied considerably. Some participants explicitly attributed a substantial portion of their motivation and cessation success to the application:

Conversely, other participants reported limited or no use of the application, indicating that they did not perceive a sustained need for its support (“Because I just did not need it” [Participant 5, position 46‐48]) or expressing doubts regarding its efficacy:

This heterogeneity in perceived utility, ranging from the app constituting a decisive treatment component to being perceived as unnecessary or ill-fitting, points to individual differences in receptiveness to digital treatment components rather than a uniform response to the app itself. For some participants, this reduced receptiveness extended beyond the specific application to a more general reluctance toward mobile applications:

Beyond their evaluation of specific treatment components, participants also articulated a range of recommendations for optimizing the cessation treatment. Several of these recommendations pointed toward a recurring tension between the standardized structure of the intervention and participants’ individually fluctuating needs, particularly with respect to treatment timing and intensity. For instance, participants suggested that the treatment could be adapted to better accommodate periods of heightened psychological strain:

Several participants emphasized the importance of flexible scheduling, noting discrepancies between the standardized frequency of sessions and their personal needs:

Similarly, participants also recommended generally increasing the intensity and duration of treatment appointments, specifically regarding the time available for conversations to enable discussing certain topics more in depth:

A subset of participants highlighted the potential values of tailored follow-up appointments for individuals concerned about acute relapse:

Taken together, these accounts suggest that the standardized format of guideline-conform treatment may itself introduce distinct challenges for individuals with comorbid mental disorders, particularly regarding the timing, intensity, and individualization of support. Beyond the structure and delivery of the treatment itself, participants also identified the need for enhanced awareness and outreach, noting that promotion of cessation programs, particularly for individuals with mental comorbidities, was insufficient, but could increase uptake among those who might otherwise remain unaware of available resources:

In sum, participants had a broad spectrum of perceptions of the smoking cessation treatment in this overarching theme. Overall, experiences were predominantly positive, particularly with respect to the manual-based intervention and the psychotherapeutic context. The adjunctive app elicited more mixed responses, particularly regarding its utility. Nonetheless, participants frequently characterized study participation as akin to therapeutic engagement. Importantly, they provided a range of recommendations for optimizing the intervention, emphasizing the need for greater individualization to accommodate personal circumstances and psychological states, as well as intensified support during critical phases of cessation.

Participants’ accounts challenge binary notions of cessation success versus failure. This nonlinear pattern of abstinence, reduction, relapse, and shifts in use is in line with process-oriented models of behavior change, such as the transtheoretical model [50,51], which conceptualizes relapse as an integral component rather than an endpoint. From a qualitative perspective, participants’ narratives suggest that subjective success was in several cases defined through increased awareness, perceived agency, or harm reduction rather than sustained abstinence alone. These findings underscore the importance of distinguishing between clinically defined outcomes and experientially meaningful change, particularly in populations with complex psychosocial needs. Sustained abstinence remains the primary therapeutic goal, as reflected in current treatment guidelines [7]; however, for individuals with comorbid mental disorders who struggle to achieve full abstinence, smoking reduction and nicotine substitution may serve as pragmatic intermediate steps, potentially easing craving and supporting eventual quit attempts [52,53], though evidence that reduction independently delivers long-term health benefits without eventual abstinence remains limited [52]. Accordingly, the present findings suggest that treatment frameworks for this population may benefit from complementing abstinence-focused goals with harm reduction perspectives that recognize reduction and substitution as pragmatically valuable steps within a broader cessation trajectory.

Changes in smoking behavior were closely intertwined with changes in mental well-being. Improvements in mood, energy, and psychological stability following abstinence or reduction were commonly attributed to feelings of pride, accomplishment, and mastery, closely mirroring Bandura’s [54] concept of self-efficacy: successful cessation attempts can be understood as “mastery experiences” that strengthened beliefs in one’s capacity for self-regulation and coping. In this sense, smoking cessation extended beyond smoking behavior change to become an identity-relevant experience that reinforced agency and self-confidence.

At the same time, early-abstinence strain (withdrawal, heightened negative affect) was typically framed as intense but time-limited, and relapse-related guilt or disappointment as transient and proportionate; neither escalated into broader crises nor affected core mental health symptoms, consistent with evidence that cessation does not generally worsen, but may improve mental health outcomes among individuals with mental disorders [33,34]. Rather, participants’ accounts suggest that distress appeared cognitively integrated into a broader narrative of change, enabling continued engagement despite setbacks, while increases in self-efficacy and perceived agency suggested positive downstream effects on the psychotherapeutic process itself, a hypothesis further examined in the embedded RCT by Sünkel et al [43]. These findings do not support the assumption that cessation or relapse inherently destabilizes individuals with mental disorders; concerns about severe emotional destabilization should therefore not be considered a general contraindication to recommending smoking cessation in this population.

A central barrier to cessation concerned the perceived functionality of smoking, which served emotion regulation, stress relief, cognitive activation, time structuring, and social facilitation—consistent with negative reinforcement and affect regulation models of addiction, which emphasize smoking’s role in alleviating aversive internal states [55]. Importantly, several participants found it helpful when these functions were explicitly acknowledged within the intervention, as this validation supported autonomous decision-making rather than framing smoking solely as maladaptive, resonating with motivational interviewing’s nonjudgmental exploration of ambivalence and respect for autonomy [56,57]. Participants also highlighted interventions aimed at developing concrete alternatives for coping and stress management (eg, progressive muscle relaxation) as particularly helpful, underscoring the importance of identifying and practicing situation-specific alternatives. For participants with mental comorbidity, concerns about losing a primary coping mechanism were especially salient and often persisted despite psychoeducation about the benefits of cessation, pointing to the psychological complexity of cessation in this population and the need for more tailored interventions. At the same time, the strong habitual and automatic embedding of smoking behaviors represents a nontrivial barrier to change, suggesting that cessation may require not only reflective and verbal interventions but, in some cases, complementary approaches that directly target automatic action tendencies. Cognitive bias modification, which aims to retrain maladaptive approach biases at a motoric level, has been proposed and empirically examined in smoking cessation [58-60] and may therefore represent a useful adjunct to interventions primarily focused on reflective decision-making.

Motivation emerged as highly fluctuating across cessation trajectories. Although intrinsic motivation and readiness to change were frequently described as important at treatment entry, participants’ accounts clearly indicate that motivation was continuously shaped and reshaped throughout the cessation process. Intervention components such as motivational analyses, CO feedback, and early abstinence successes were experienced as reinforcing commitment and engagement, underscoring the situational and processual nature of motivation as a state rather than a stable trait. This interpretation is consistent with empirical evidence suggesting that baseline, trait-like motivation alone is not a reliable predictor of smoking cessation success. For example, Ussher et al [61] found that the strength of motivation to quit assessed prior to treatment did not predict abstinence among treatment-seeking smokers, yet dependence severity did. At the same time, motivational processes unfolding during the quit attempt itself may be more relevant for understanding lapse and relapse. Motivation appears to serve different functions at different stages of behavior change: while motivation measures such as the Motivation To Stop Scale show strong predictive validity for initiating quit attempts over several months [62], they may be less informative for predicting sustained abstinence. This distinction closely mirrors participants’ narratives, in which motivation was described as sufficient to initiate a quit attempt but vulnerable to contextual influences once abstinence was underway.

Conceptualizing motivation as a dynamic state rather than a stable trait also provides a natural link to self-determination theory [63], which has also received empirical support in the context of smoking cessation [64]. Rather than assuming enduring motivational dispositions, the theory emphasizes the situational and context-dependent regulation of motivation as a function of momentary satisfaction or frustration of basic psychological needs for autonomy, competence, and relatedness. In this sense, self-determination theory offers a framework for understanding why motivation during smoking cessation is experienced as unstable yet responsive to intervention components. Consistent with this perspective, participants’ accounts highlighted the importance of being able to make autonomous decisions, experiencing competence through early successes, and feeling supported by others. In this context, Niemiec and colleagues’ [64] concept of motivational attunement is particularly informative. Attending to daily motivational fluctuations and responding with timely, need-supportive interventions aligns closely with participants’ experiences. In participants’ accounts, feeling heard and supported coincided with greater engagement and readiness for change. The motivational decline following the end of structured treatment highlights the importance of ongoing relational support and accountability (eg, booster sessions). Taken together, these findings suggest that future interventions may benefit from adopting motivation-sensitive designs in which the intensity, timing, and form of support are flexibly adjusted to individuals’ momentary motivational states (eg, ecological momentary assessment approaches as described by Shiffman [65]).

Smoking cessation was embedded within broader social and contextual environments, with social networks acting as both facilitators of and barriers to change. In this study, significant others who smoked were predominantly experienced as relapse risk factors—observing friends or family smoke increased urges and, in some cases, reinforced participants’ own smoking—while supportive relationships provided emotional and practical assistance during acute craving. Even with explicit encouragement to quit, smoking-normative environments and shared smoking rituals often undermined cessation efforts, illustrating social context’s complex, sometimes ambivalent influence on behavior change. These findings align with social practice theory [66], which frames smoking as a practice organizing interaction, time, and relational proximity. From this perspective, cessation requires not only individual self-regulation but also the renegotiation of social roles, routines, and meanings. Contextual factors such as timing, stress exposure, and entrenched habits further shaped participants’ experiences, highlighting the interplay between individual agency and situational constraints.

Clinically, these findings suggest that smoking cessation interventions may benefit from explicitly addressing the social embeddedness of smoking. Supporting individuals in navigating high-risk social contexts, renegotiating shared smoking rituals, and mobilizing supportive relationships in ways that foster relatedness without exerting pressure may help reduce the social costs of cessation while strengthening motivation and persistence. In other areas of addiction treatment and psychotherapy, the inclusion of partners or family members is a common practice and has been shown to improve engagement and treatment outcomes [67].

A particularly salient finding concerns participants’ heterogeneous views on the indication of cessation treatment for individuals with comorbid mental disorders, ranging from strong endorsement to pronounced skepticism about its feasibility and safety during periods of heightened vulnerability, reflecting broader clinical and cultural narratives within mental health care. Concerns primarily centered on the perceived risk that cessation could exacerbate psychiatric symptoms, destabilize emotion regulation, or interfere with ongoing psychotherapeutic processes. Several participants explicitly referenced assumptions commonly attributed to health care professionals, such as the belief that smoking cessation constitutes an additional burden during acute distress or early treatment phases. Notably, these concerns persisted despite participants’ own experiences frequently contradicting such assumptions, as most reported improvements in mental well-being or only short-lived adverse effects following cessation attempts. This discrepancy highlights a critical tension between anticipated risk and experienced outcomes. The persistence of concerns despite predominantly disconfirming personal experiences can be understood in light of the ViolEx model of expectation maintenance and change [68,69]. According to this framework, expectations often remain stable even after violation due to cognitive immunization processes, in which discrepant experiences are reinterpreted as exceptions rather than prompting accommodation. In the present data, immunization can be interpreted in person-bound attributions (eg, cessation being feasible “for me, but not for more severely ill individuals”) and temporal qualifications (eg, cessation being possible only because it was “the right time”). Such interpretations preserve the overarching expectation that smoking cessation poses a risk during mental health treatment, despite experiential evidence to the contrary. Extensions of the ViolEx model [70,71] emphasize that expectation change requires not only experiential violation but also the explicit reduction of immunizing explanations. From this perspective, the findings suggest that integrating expectation-focused reflection into smoking cessation interventions may be beneficial for modifying anticipatory risk beliefs and facilitating broader acceptance of cessation within psychotherapeutic care. While participants acknowledged that cessation can be demanding, their narratives largely challenge the notion that smoking cessation is inherently contraindicated for individuals with mental health difficulties. Instead, the findings suggest that perceived risks may stem less from cessation itself than from insufficient support, suboptimal timing, or a lack of contextual sensitivity in treatment delivery.

These findings align with current clinical guidelines recommending that individuals with comorbid mental disorders should receive smoking cessation support on equal terms with the general population [7]. However, smoking continues to be framed by many health care professionals as a “lifestyle issue” rather than a life-threatening condition, and qualitative research in psychiatric care settings similarly documents persistent misconceptions among practitioners, including beliefs that cessation may harm patients with mental disorders [32]. The present study extends this literature by showing that such misconceptions are experienced by patients themselves, even when their own cessation attempts led to positive or stabilizing mental health outcomes [33,34].