Substance use disorder (SUD) affects more than 23 million Americans and claims more than 70,000 lives annually. With 40-60% relapse rate, SUD patients are high hospital utilizers, 65% of the incarcerated population, and are at high-risk for overdose and deaths. There is a pressing need for research in this area to advance beyond traditional pharmacological and behavioral therapies toward a greater focus on the mechanisms of risk for relapse and to improve personalization for SUD treatment.

Neuromodulation has shown promise to stimulate neuronal growth without any of the side effects of medications or electroconvulsive therapy. Using transcranial direct current stimulation (tDCS) to modulate cortical activity has shown to be a viable therapy in medicine-resistant depression, to reduce opioid cravings, and impulse control.

The proposed research plans to recruit 30 subjects with a history of substance use disorder (SUD). This may include a history of addiction to opioids, cocaine, and barbiturates. Addiction to alcohol and cannabinoids (marijuana) will be excluded from this study. Following recruitment and consent, the subject will be administered an EEG, Acceptance Commitment Therapy exercise followed by EEG, and a BIS-11 Survey measuring levels of impulsivity. During the next week, the patient will undergo 5 visits consisting of a pre-EEG, tDCS, and post-EEG. Half of the subjects (n=15) will receive treatment, while the other half will be in a sham group. After the completion of the 5 tDCS visits, the patient will again be administered an EEG, ACT exercise followed by EEG, and a final BIS-11 survey measuring for end impulsivity levels.

The primary objective of the proposed study is to determine the impact of tDCS on impulsivity in SUD subjects. The long-term goal of the study is to address the underlying neurobiological deficiencies caused by SUD and provide a more personalized adjunctive SUD treatment.

Aim 1 will establish the extent of change to brain waves during tDCS+ACT treatment sessions in both arms while also performing the stop signal task. This aim will be achieved by capturing baseline EEG readings of the entire brain for subjects in both arms and also capturing EEG readings during the treatment phase and at the final study visit 1-week post and comparing between and within results.

Aim 2 will determine whether a change to self-reported impulsiveness occurs as a result of tDCS or tDCS and ACT exercise accompanied by the stop signal task. The investigators will achieve this aim by comparing the baseline Barratt Impulsiveness Scale (BIS-11) survey results of subjects in treatment and placebo arms to BIS-11 survey results on the final day of the 5 days of treatment and one week later, enabling investigators to determine any short-term change or durable change to impulsivity.

Aim 3 will measure whether the tDCS system, tKIWI, results in any unwanted side effects or adverse events. The investigators will achieve this aim by monitoring subjects' vitals during the entire session and evaluating results of a questionnaire after each treatment session and after the final study visit, enabling us to capture reported discomfort.

Inclusion Criteria:

• Age: 18-79 years old
• Gender: Any
• Ethnicity: Any
• Diagnosis of substance use disorder and a recent history of substance use (<24 months last use), but not currently reporting use.

Exclusion Criteria:

• Diagnosis (as defined by DSM-IV) of: any psychotic disorder (lifetime); eating disorder (current or within the past year); obsessive compulsive disorder (lifetime)); mental retardation.
• History of drug or alcohol abuse or dependence (as per DSM-IV criteria) within the last 3 months (except nicotine and caffeine).
• Subject is on regular benzodiazepine medication which it is not clinically appropriate to discontinue.
• Subject requires a rapid clinical response due to inanition, psychosis or high suicide risk.
• Neurological disorder or insult, e.g., recent stroke (CVA), which places subject at risk of seizure or neuronal damage with tDCS.
• Subject has metal in the cranium, skull defects, or skin lesions on scalp (cuts, abrasions, rash) at proposed electrode sites.
• Female subject who is pregnant.
• Participants who are not fluent in English will not be included in the trial for safety reasons: a) It is usually not possible to have an interpreter reliably available every weekday for up to 4 weeks and it is not safe to give tDCS to a subject who cannot tell us immediately of any side effects; Note that translation of the proposed ACT activity into English has not been validated and that we cannot be confident that they would be accurately translated and validated.
• Minors
• Older than 79 years old
• last use >24 months
• history of EEG or any electrical implant (i.e. pacemaker)
• history of Parkinson's, diagnosis of bipolar, schizophrenia/schizo-affective d/o, OCD, epilepsy, alzheimers
• primary drug of choice alcohol or marijuana
• taking antipsychotic drugs

The deidentified raw data will be stored for future research. The results will be published and shared with the industry partner, ni20, inc.

Only the study staff will have access to the randomization information and study participants in each arm will not be informed which arm they are in. The sham group will receive 10 seconds of .5mA at the initiation of each of the three "ramp-ups," after which the current will be turned off. This is to maintain a blind trial.