The proposed clinical trial aims to examine the efficacy of an online-based self-help intervention for auditory hallucinations in persons with psychotic disorders. The intervention is primarily based on Metacognitive Training (MKT) and Mindfulness-Based Group Therapy (MBGT). The investigators will utilize a mixed-method study design within a randomized controlled trial. The intervention group will be compared with a waitlist-control group (WL-TAU). Both study conditions are allowed to continue standard scheduled treatment. The aim is to analyze the efficacy of and the subjective satisfaction with the intervention, based on self-report assessments evaluated from baseline (T0) to post-intervention after 6 weeks (T1).

The investigators will identify eligible participants at various outpatient departments, suitable support groups, online platforms, and social media. An eligibility screening (in person or by telephone) to ensure the inclusion criteria and to introduce the study is held by the study assistant. All participants must sign an informed electronic consent after written and verbal study clarification. If persons are eligible for participation, they will be randomized according to a randomization plan by the electronic database RedCap. Due to the psychotherapeutic nature of the study, there will be no blinding. Participants in both study conditions will carry out self-reported measurements (online) at baseline (T0) and after the intervention phase of 6 weeks (T1). With an anticipated n = 25 of persons from the intervention group, there will be additionally conducted semi-structured interviews at T1 that aim to examine specific patterns of auditory hallucinations and satisfaction with the intervention. The final sample of the qualitative research part will be determined according to the principle of saturation (content-related). The data management plan includes standard procedures for data-handling such as using anonymized identification codes for patient data. Besides, the participants have the right to access their data, and the right to claim an annihilation. The data is being saved in an online database, only allowing researchers involved in the study to access the data.

Inclusion Criteria:

• current experience of auditory hallucinations that appear at least once a week (measured over the PSYRATS).
• diagnosis of a schizophrenia-spectrum disorder according to the Diagnostical and Statistical Manual (5th edition) and/or the International Statistical Classification of Diseases and Related Health Problems (ICD-10), code F2x.x. In case of a suspected diagnosis or missing clinical diagnostic, we will apply the Mini-International Neuropsychiatric Interview (M.I.N.I.).
• stable psychiatric medication over at least one month, slight changes of dosage are allowed and will be evaluated by a trained psychiatrist.
• ability to give informed consent.
• willingness and ability to engage in the psychotherapeutic self-help intervention.
• availability of a mobile device and internet access.

Exclusion Criteria:

• neurological disorders that may affect cognitive functioning and condition after severe traumatic brain injury.
• acute suicidality, assessed at the previous screening procedures.
• auditory hallucinations in the context of other primary diagnoses e.g., post-traumatic stress disorder or borderline personality disorder.
• acute substance abuse other than nicotine and prescribed medication.
• current electroconvulsive therapy.
• current inpatient or day-care treatment.