The goal of this clinical trial is to evaluate whether a brief group-based psychological intervention using cognitive-behavioral therapy (CBT) helps people in prison quit smoking. Researchers will compare this intervention to a health education program and a control group (waitlist) to see which approach is most effective.

The main questions this study aims to answer are:

• Does the CBT-based group intervention help more participants quit smoking compared to the health education group and the control group?
• Do participants in the CBT-based group intervention smoke fewer cigarettes per day one month after the intervention compared to the other groups?
• Do participants in the CBT-based group intervention have lower nicotine dependence ?
• What individual factors (e.g., motivation to quit, nicotine dependence, craving intensity, self-efficacy, withdrawal symptoms, anxiety, depression, ADHD, and PTSD) predict success in the CBT and Health education groups?

Participants will be randomly assigned to one of three groups:

• CBT group: Three group sessions (1.5 hours each) using CBT and motivational approaches to quitting smoking.
• Health education group: One group session (1 hour) providing information on smoking and its health risks.
• Control group: No intervention for three months (waitlist). All participants will complete an initial assessment, attend their assigned group sessions, and return for follow-up visits at 1 month and 3 months. Their smoking status will be measured through self-reports and carbon monoxide (CO) expired levels.

Inclusion Criteria:

• Male individuals currently incarcerated at Maison d'Arrêt Paris-La Santé.
• Aged 18 years or older at the time of inclusion.
• Current smoker, defined as having smoked daily in the past 30 days, or having an occasional smoking pattern of at least 5 cigarettes during the past 30 days.
• Able to speak and understand French well enough to follow the study procedures and actively participate in group sessions.
• Sentence length of at least 6 months, or if in pretrial detention, having a scheduled trial date within at least 6 months.

Exclusion Criteria:

• Age under 18 years at the time of inclusion.
• Inability to speak and understand French well enough to follow the study procedures and actively participate in group sessions.
• Sentence length of less than 6 months, or if in pretrial detention, having a scheduled trial date in less than 6 months or no available information about the trial date.
• Severe cognitive impairment that affects comprehension and participation in the study.
• Unstable psychiatric conditions (including acute psychotic disorders, severe mood disorders, severe anxiety disorders).
• Individuals under legal guardianship or conservatorship (e.g., placed under tutelage, curatorship, or temporary guardianship).

Investigators do not plan to share individual participant data (IPD) for this study. The protocol submitted to the Ethics Committee (CPP) does not include any specific provision regarding data sharing, and participants were neither informed nor consented to such use. In accordance with ethical and regulatory requirements, as well as principles of confidentiality and data protection, investigators are therefore unable to make these data available to other researchers.