Leveraging process models of self-regulation to understand unassisted smoking cessation

Unassisted smoking cessation, where individuals quit without formal support such as nicotine replacement therapy or professional assistance, remains a prevalent yet little understood pathway to quitting. The current thesis investigates unassisted cessation through the lens of motivation and self-regulation, combining qualitative and quantitative methods to develop a detailed, theoretically grounded understanding of why and how people quit smoking on their own. Chapter 1 introduces the public health context of smoking and cessation, with a particular focus on unassisted quitting in the UK. Drawing on Self Determination Theory, the Health Belief Model, and self-regulation frameworks, the chapter outlines the psychological and behavioural mechanisms that may under pin unassisted cessation. It introduces the concept of “polyregulation”—the use of multiple strategies to support behaviour change—and proposes an integrative approach to studying this phenomenon across the thesis. Chapter 2 presents a qualitative study exploring the why behind unassisted cessation using reflexive Thematic Analysis of interviews with 32 quitters. Findings reveal that motivations were often tied to life events, identity changes, and a desire for regaining control over one’s life, with health scares, social roles (e.g., parenthood), and a rejection of dependence on nicotine influencing the quit attempt. These narratives highlight nuances beyond simplistic theoretical binaries of internal (e.g., arising from personal interest) versus external (e.g., contingent on rewards or disapproval from others) motivation. Chapter 3 turns to the how of unassisted cessation, exploring the behavioural strategies employed by unassisted quitters through analysis of the same qualitative dataset using the Process Model of Self-Control and the Behaviour Change Taxonomy. Participants reported a diverse “toolbox” of situational and cognitive strategies, including environmental restructuring, distraction, cognitive reappraisal, and habit reversal. The findings highlight the sophistication of unassisted quit attempts, where individuals actively manage behaviour change using combinations of strategies—reaffirming the notion of polyregulation. Chapter 4 extends this work through a cross-sectional survey of 498 quitters(assisted and unassisted), examining associations between quitting method, motivation, strategy use, and socioeconomic status (SES). Results indicate that unassisted quitters were more autonomously motivated than their assisted counterparts, particularly among individuals from lower SES backgrounds. While low SES was generally linked to reduced motivation and fewer strategies, unassisted quitting appeared to buffer against this trend, suggesting that autonomy may be a resilience factor in cessation. Chapter 5 follows 226 quitters over a 12-week period to investigate whether autonomous motivation and strategy use predict smoking outcomes. Although autonomous motivation was linked to greater strategy use, these variables did not significantly predict smoking behaviour over time. The findings raise questions about the predictive strength of these variables for smoking cessation, despite their relevance for understanding the process of quitting as established in the previous chapters. Chapter 6 uses a multiverse analysis to re-visit these findings, systematically varying analytical decisions to assess the robustness of associations between motivation, strategy use, and smoking outcomes. While baseline motivation and strategy use were modestly linked, their associations with cessation outcomes remained weak across specifications. One consistent finding was that baseline perceived competence predicted lower nicotine dependence at follow-up. This approach supports the validity of previous null findings and provides transparency around analytical uncertainty. Finally, Chapter 7 synthesises insights across all studies, proposing a psychological profile of the unassisted quitter as someone driven by internalised values, identity transitions, and strategic behaviour change. The thesis discusses tensions between narrative and predictive accounts of cessation, concluding with the lessons learned, limitations of the studies, and directions for future research.