Substance use disorder (SUD) is a global problem with serious psychological, physiological, and social consequences. Seeking professional help is often delayed due to a lack of self-recognition of addiction, frequently sustained by self-deception. Although self-deception is a core feature of SUD, the mechanisms underlying it remain insufficiently studied. This research examines the role of impulsivity and self-efficacy in predicting self-deceptive behaviors—manipulation and mystification—in individuals undergoing addiction rehabilitation. The sample consisted of 122 Spanish participants from therapeutic communities (Mage = 44.99, SD = 10.58; 82.8% male) who completed the Self-Deception Questionnaire (SDQ-12), the Impulsive Control Scale Ramón y Cajal (ECIRyC), and the Drug Taking Confidence Questionnaire (DTCQ). Results showed that impulsivity significantly predicted both manipulation and mystification. Manipulation was also associated with self-efficacy in managing temptation and duration of addiction, highlighting its multifaceted nature. In contrast, mystification was predicted solely by impulsivity, suggesting a stronger dependence on internal psychological processes rather than contextual factors. These findings underscore the importance of targeting impulsivity and enhancing self-efficacy in addiction treatment. Interventions such as Cognitive Behavioral Therapy (CBT), Acceptance and Commitment Therapy (ACT), and mindfulness-based approaches may be particularly effective in reducing self-deceptive behaviors and supporting long-term recovery.