Cannabis use disorder is a frequent comorbidity of schizophrenia, associated with increased symptoms and less adherence to therapy. Validated care has limited effectiveness in this population and development of new management strategies seems necessary. Transcranial direct current stimulation (tDCS) has shown beneficial effects in both schizophrenia, substance use disorder and, in a less extent, in nicotine addiction in schizophrenic subjects. It is interesting to test if that 10 sessions of anodal stimulation of the right dorsolateral prefrontal cortex (DLPFC) and cathodal stimulation of the medial prefrontal cortex (MPFC) (by increasing control and modulating reward system), will reduce, in 110 schizophrenic subjects, cannabis consumption, and secondly craving, addiction severity, schizophrenic symptoms and improve global functioning. It is possible that these clinical effects will be associated with changes in certain cognitive functions and cerebral connectivity.

Stimulation will be performed using a Neurocan DC-Stimulator Plus with two 7×5 cm sponge electrodes soaked in a saline solution. Electrodes will be placed in accordance with the international 10-20 electrode placement system: the anode over F4 (right DLPFC), the cathode over Fp1 (MPFC). The stimulation level will be set at 2 mA for 20 minutes during stimulation sessions twice a day (separated by at least 3 hours) for 5 consecutive weekdays.

The control group will receive the sham stimulation following the same regimen, using the sham procedure which has been developed by the manufacturer of the tDCS material, allowing sensations to be felt in the scalp which are the equivalent to those of the active stimulation. The same device will be used for both the sham and the active procedures.

Inclusion Criteria:

• Schizophrenia diagnostic according to DSM (Diagnostic and Statistical Manual of mental disorder) 5 criteria, without change in psychotropic treatment since at least 4 weeks
• Moderate to severe cannabis use disorder according to DSM 5 criteria and active consumption during the last 7 days
• Subjects motivated to reduce or quit their cannabis consumption
• Patients with ambulatory compulsory care may be included

Exclusion Criteria:

• Other substance use disorder, excluding nicotine, according to DSM 5 criteria
• Other current psychiatric disorder according to DSM 5 criteria, excluding personality disorder
• Inpatient hospitalization
• History of head injury, neurological disorder with cerebral consequence or severe unstable somatic disorder
• Pregnancy or no contraception
• Contraindications for tDCS and/or MRI (implanted material, uncontrolled epilepsy, intracranial hypertension)

• active tDCS stimulation. Patients will receive 10 sessions of tDCS over 5 consecutive days, at a frequency of 2 sessions per day spaced at least two hours apart, at an intensity of 2mA, for 20 minutes each.
• tDCS placebo stimulation. Patients will receive 10 sessions of tDCS over 5 consecutive days, at a frequency of 2 sessions per day spaced at least two hours apart, following an identical procedure (tracking, then wearing the device for 20 minutes) but with actual stimulation provided during the first 40 seconds.