In this study, investigators are testing whether a higher dose of a non-invasive brain stimulation technique, called transcranial direct current stimulation (tDCS), can be safely used in people with depression. Participants will come to the Brain Stimulation Lab and receive mild electrical stimulation through electrodes placed on their scalp.

The study begins with a safety run-in, where the first few participants will receive stimulation at gradually increasing levels (2, 4, and 6 milliamps) while being closely monitored. If no serious side effects are found, later participants will receive repeated 6 milliamp sessions for 5 days total. Investigators will check skin comfort, mood, and overall tolerability after each session.

Major depressive disorder (MDD) remains one of the leading causes of disability worldwide, with many patients experiencing inadequate response to currently available treatments. Transcranial direct current stimulation (tDCS) has shown promise as a non-invasive, well-tolerated neuromodulation technique for depression, but nearly all prior studies have used lower current intensities (≤2 mA). Preliminary modeling and experimental work suggest that higher current dosing may be necessary to achieve sufficient engagement of cortical targets and produce stronger clinical effects.

The present study is designed to address this gap by systematically evaluating the safety, tolerability, and feasibility of high-dose tDCS delivered at 6 mA in adults with MDD. Establishing safety at this higher intensity is a critical step before pursuing larger efficacy trials. By carefully monitoring adverse events and skin integrity during an initial run-in phase, this study provides an evidence base for whether 6 mA tDCS can be safely implemented in a clinical population.

Inclusion Criteria:

• Ages 18-70.
• Current MDD diagnosis (MINI v7).
• Baseline PHQ-9 > 9.
• Capacity to consent
• Fluent English.

Exclusion Criteria:

• Bipolar or psychotic disorder
• Primary anxiety disorders without concomitant major depression as defined above
• Current significant suicidal ideation or behaviors require a higher level of care.
• Use of neuromodulation therapies (e.g., ECT, TMS, VNS) within the past 6 months.
• History of seizures, implanted cranial/ cardiac metal, or neurosurgery.
• Use of medications that significantly reduce seizure threshold
• Frequent/severe HA
• Personal history of head trauma, concussion, or TBI
• Catatonic or otherwise unable to perform the consent process
• Current alcohol or substance-use disorder (moderate-severe).
• Any non-uniformities in the skin under the electrode site, including eczema, severe rashes, hyperhidrosis, communicable skin disorders, sensitive skin (ex. eczema, severe rashes), blisters, open wounds, burns including sunburns, cuts or irritation (e.g. due to shaving), or other skin defects or lesions, as determined by clinical personnel
• Pregnancy (urine test required for women of childbearing potential).