Participants randomized to the CBT group will receive a minimum of 13 and a maximum of 22 sessions of individual formulation-based CBT. It will be delivered by psychologists trained in CBT, according to a manual that will be available soon. Prior to intervention, a behavioral assessment is conducted to operationalize each case's clinically relevant behaviors, antecedents, and maintenance stimuli. Each case will be formulated and presented to the participant in simple and easy to understand language. To illustrate this, a schematic formulation of the typical case of an adult with ADHD is shown in Figure 2. Specific behavioral goals will then be agreed upon for each participant. To achieve these goals, various treatment strategies will be presented in the following sessions. The choice of strategies, the order in which they are applied, and the duration of each module will be customized for each participant according to the case formulation.

The Spanish participants assigned to the active control group will receive the PROBECO. It is a group program designed by the Spanish Penitentiary Agency for its application with inmates convicted of different types of violent crimes . Its main goals are to eradicate criminal behavior and reduce recidivism, to modify the relevant dynamic risk factors related to general delinquency, and to introduce new social skills and prosocial values. It consists of four phases: (I) general intervention: aimed at the acquisition of social skills; (II) specific intervention: consists of four specific educational itineraries; (III) relapse prevention; (IV) follow-up.

Similarly, German participants will be assigned to a special type of prison known as a social therapeutic facility, where they will undergo compulsory psychotherapy focused primarily on relapse prevention.

Spanish participants in the active control group will undergo the PROBECO program, designed by the Spanish Penitentiary Agency for various violent crimes. It aims to eradicate criminal behavior, reduce recidivism, and teach social skills. It has four phases.

German participants will be placed in social therapeutic facilities for compulsory psychotherapy focused on relapse prevention.

This is considered one of the primary outcomes. The CAADID is a structured interview divided into two parts. Part I may be self-administered or clinician-administered and collects information on the subject's demographic history, developmental history, associated risk factors, and comorbidity, while Part II must be administered by a trained clinician and assesses DSM-IV criteria for ADHD in adults. Only Part II will be used for the study, as information on patient history is not relevant for measuring response to interventions.

This will be the primary criminological outcome. Police records will be checked every 6 months after the end of treatment to look for new arrests. We will also try to check court and prison records for new convictions and incarcerations. However, access to this information may be very limited in European criminal justice systems, so it may be difficult to obtain.

Is a three-item observer-rated scale that measures illness severity, global improvement or change, and therapeutic response. It is a widely used, robust measure of efficacy in clinical trials. The global functioning outcome provides a measure of the impact that symptoms have on daily functioning in life domains (e.g., social, family, work, personal, and academic, among others).

In order to measure adherence more objectively, attendance at treatment sessions and completion of homework assignments are systematically recorded by the therapist at each session.