Self-stigma is a major barrier to personal and clinical recovery in people with mental illness. Although psychosocial interventions have been developed to reduce self-stigma, the exploration of group CBT-based interventions for hospitalised patients are less represented. The purpose of this trial is to investigate the effectiveness of a group CBT-based intervention aiming to reduce self-stigma and improve recovery-related outcomes such as self-esteem, stigma resistance and sense of coherence, which comes down to saying, "I am what I am". A total of 104 patients admitted to the inpatient therapy were recruited to participate in a randomised controlled clinical trial, and 77 participants (46 in the intervention group and 31 in the control group) completed the trial. Constructs of interest were measured before and after the intervention. The results showed that the evaluated intervention was effective in improving sense of coherence and stigma resistance, compared to treatment as usual (TAU). The level of self-stigma significantly decreased in both the intervention and control groups, but no statistically significant difference was observed between the groups. The limitations of the study include: the lack of assessment of the sustainability of the effects of therapy (follow-up), the presence of intensive interventions of the ward's programme and patients pre-qualified for the ward based on admission criteria. The intervention "I am what I am," has proven to be effective, especially in increasing the level of personal resources needed to build clinical and personal recovery and to counteract the negative consequences of self-stigma.