Transcranial Direct Current Stimulation (tDCS) has emerged over the last two decades as one of the most widely studied forms of non-invasive brain stimulation. Unlike electroconvulsive therapy (ECT) or repetitive transcranial magnetic stimulation (rTMS), tDCS uses low-intensity direct current (typically 1–2 mA) delivered through scalp electrodes to modulate cortical excitability. Depending on polarity, anodal stimulation increases excitability while cathodal stimulation reduces it.

While tDCS is still considered investigational in many countries (including the United States, where the FDA has not formally approved protocols for psychiatric or neurological conditions), its evidence base is steadily expanding. Multiple randomized controlled trials and meta-analyses have now established best-practice protocols for certain disorders, which are being tested globally in research and clinical innovation settings.

🔹 1. Major Depressive Disorder (MDD)

• Electrode montage:

  • Anode → Left DLPFC (F3 in 10–20 EEG system)

  • Cathode → Right supraorbital (Fp2) or sometimes right DLPFC

• Parameters:

  • Current: 2 mA

  • Duration: 20–30 minutes

  • Frequency: 5 sessions/week

  • Total: 10–20 sessions (some intensive trials use 2/day “spaced” protocols)

• Evidence:

  • Multiple RCTs and meta-analyses show small to moderate antidepressant effects.

  • Best results are seen in non–treatment-resistant depression and when tDCS is combined with antidepressant medication or psychotherapy.

• Clinical tip: Use depression rating scales (HAM-D, MADRS, PHQ-9) for monitoring.

🔹 2. Stroke Rehabilitation (Motor Recovery)

• Electrode montage:

  • Anode → Ipsilesional motor cortex (C3/C4)

  • Cathode → Contralesional M1 or contralateral supraorbital

• Parameters:

  • Current: 1–2 mA

  • Duration: 20 minutes

  • Frequency: daily (5×/week) for several weeks

  • Always combined with task-specific physiotherapy

• Evidence:

  • Modest but consistent improvement in upper-limb motor function when paired with rehabilitation.

  • Results are stronger in subacute stroke than chronic stroke.

• Clinical tip: Never use as stand-alone therapy; always pair with physiotherapy or occupational therapy.

🔹 3. Chronic Pain Syndromes

• Electrode montage:

  • Anode → Primary motor cortex (M1, C3/C4) contralateral to pain

  • Cathode → Supraorbital

• Parameters:

  • Current: 1–2 mA

  • Duration: 20 minutes

  • Frequency: daily or alternate days, 5–10 sessions

• Evidence:

  • Meta-analyses show short-term analgesia in fibromyalgia, neuropathic pain, and spinal cord injury pain.

  • Durability of effect is variable; booster sessions may be required.

• Clinical tip: Combine with relaxation training or physiotherapy for better outcomes.

🔹 4. Schizophrenia (Auditory Hallucinations)

• Electrode montage:

  • Cathode → Left temporoparietal junction (T3/TP3 area)

  • Anode → Left DLPFC (F3) or contralateral supraorbital

• Parameters:

  • Current: 2 mA

  • Duration: 20 minutes

  • Frequency: daily for 1–2 weeks (some protocols: twice daily)

• Evidence:

  • Several RCTs show reduction in auditory verbal hallucination severity.

  • Effects are modest but clinically meaningful in certain patient groups.

• Clinical tip: Monitor hallucination severity scales (e.g., PSYRATS).

🔹 5. Obsessive–Compulsive Disorder (OCD)

• Electrode montage options:

  • Anode → SMA / pre-SMA (FCz)

  • Cathode → Right DLPFC or contralateral site

• Parameters:

  • Current: 1–2 mA

  • Duration: 20–30 minutes

  • Sessions: 10–20 over 2–4 weeks

• Evidence:

  • Early pilot trials show improvement in compulsive symptoms, but meta-analyses highlight heterogeneity.

• Clinical tip: Combine with ERP (Exposure and Response Prevention) for maximum benefit.

🔹 6. Tinnitus

• Electrode montage:

  • Cathode or anode over temporal cortex (T3/T4)

  • Contralateral supraorbital as reference

• Parameters:

  • 1–2 mA, 20 minutes, multiple sessions

• Evidence:

  • Variable; some short-term reduction in tinnitus loudness/distress.

  • Long-term effects inconsistent.

🔹 7. Cognitive Decline / Dementia

• Electrode montage:

  • Anode → Left DLPFC (F3)

  • Cathode → Fp2 or contralateral orbitofrontal

• Parameters:

  • 1–2 mA, 20 minutes, paired with cognitive training tasks

• Evidence:

  • Mixed but promising results in mild cognitive impairment (MCI) and Alzheimer’s disease, especially when paired with working memory training.

🔹 Common Safety Guidelines

• Current intensity: 1–2 mA (do not exceed 2.5 mA in clinical research)

• Electrode size: 25–35 cm² pads (affects current density)

• Session duration: 20–30 minutes

• Side effects: Mild tingling, itching, skin redness, transient headache

• Serious risks: Rare when following standard protocols

• Contraindications: Skull defects, seizure history (caution), implanted electronic devices (pacemakers, DBS), broken scalp skin

🔹 The Take-Home Message

tDCS is a safe, low-cost, portable neuromodulation tool with a growing evidence base across psychiatry and neurology. The most robust evidence supports its use in depression, stroke rehabilitation, and chronic pain, while promising early data exist for schizophrenia, OCD, tinnitus, and dementia.

Still, it remains investigational in most countries, and clinicians should apply it within ethical frameworks, ideally as part of research or adjunctive therapy.