The investigators conducted a double-blind randomised sham-controlled study. Upon enrollment into the study, participants were randomly assigned to one of two conditions: (i) active group: anodal stimulation over the right dlPFC (n = 10) or (ii) sham stimulation group (n = 10). Participants and raters were blinded to the condition.

Subsequently, the participants were administered the IGT and the Wisconsin Card Sorting Test by a trained neuropsychologist in a quiet laboratory. A computerized version of standard IGT was used. The order of the tasks performed in a single session was randomised.

After the psychiatric and neurocognitive assessment, participants received three sessions of 20-minute active or sham anodal tDCS (once a day, every other day).

Wisconsin Card Sorting Test and a modified version of Iowa Gambling Test were readministered after the last application. The order of the tasks was randomized again. A brief questionnaire on study blinding was also administered. Safety was assessed through open-ended questions based on the tDCS adverse events questionnaire

Inclusion Criteria:

• Participants meeting Diagnostic and Statistical Manual of Mental Disorders (DSM-5) criteria for gambling disorder
• Being right-handed
• Being 18-65 years old
• Being drug-free

Exclusion Criteria:

• Current DSM-5 diagnosis of major depressive disorder
• Current or previous DSM-5 diagnosis of alcohol and substance use disorders, schizophrenia, bipolar disorder, or other psychotic disorder
• Drug Use in the past 4 weeks of any medication with known pro-convulsant action or current regular use of any psychotropic medications (benzodiazepines, antipsychotic medications, tricyclic antidepressants, anti-epileptics, mood stabilizers)
• Any history of any clinically significant neurological disorder, including organic brain disease, epilepsy, stroke, brain lesions, multiple sclerosis, previous neurosurgery, or personal history of head trauma that resulted in loss of consciousness for > 5 minutes and retrograde amnesia for > 30 minutes,
• The presence of mental retardation diagnosis (previously identified)
• Any personal or family history (1st degree relatives) of seizures other than febrile childhood seizures
• Illiteracy, deficient language or refusal to participate.