This is a monocentric, randomized pilot study conducted at the Max Planck Institute of Psychiatry, Munich. The study investigates the effects of two different intermittent theta-burst stimulation (iTBS) schedules on biological and clinical outcomes in patients with depression and comorbid Post-COVID-19 condition (PCC). Participants will be randomized into two arms, both receiving a total of 30 active iTBS sessions applied to the left dorsolateral prefrontal cortex (DLPFC) at 90% resting motor threshold using a PowerMAG 100 ppTMS stimulator:

• Standard Arm: One iTBS session per day, five days per week, over six weeks.
• Intensified Arm: Six iTBS sessions per day, approximately one-hour apart, over five consecutive days.

The primary outcomes are changes in immunological blood markers (C-reactive protein [CRP], tumor necrosis factor [TNF], interleukin-1β [IL-1β], interleukin-6 [IL-6]) and depressive symptomatology measured by Beck Depression Inventory-II (BDI-II) and Montgomery-Asberg Depression Rating Scale (MADRS). Secondary outcomes include fatigue (Fatigue Severity Scale [FSS], Fatigue Scale for Motor and Cognitive Functions [FSMC], Post-Exertional Malaise questionnaire [PEM]), sleep quality (Pittsburgh Sleep Quality Index [PSQI]), daytime sleepiness (Epworth Sleepiness Scale [ESS]), functioning (Sheehan Disability Scale [SDS]), anxiety (Beck Anxiety Inventory [BAI]) and an exploratory adverse effect screening. Follow-up assessments will be performed three days after treatment completion and again at three months post-intervention to evaluate both short- and medium-term effects. Biospecimen collection will include approximately 141 ml of peripheral blood per participant across three time points (baseline, post-treatment, +3 days). Samples will be analyzed for inflammatory markers and securely stored in the institutional biobank of the Max Planck Institute of Psychiatry in accordance with data protection and ethical guidelines. Safety and tolerability will be continuously monitored, including documentation of adverse events. The results of this pilot study are expected to provide preliminary evidence on whether accelerated iTBS protocols may exert differential effects on neuroinflammatory processes and depressive symptomatology in patients with Post-COVID-19 condition, thereby informing larger controlled clinical trials.

Inclusion Criteria:

• Age 18-65 years
• Capacity to consent (legally competent, written informed consent including data protection)
• Diagnosis of depression (at least moderate severity, BDI-II ≥ 20), including major depressive episode in bipolar disorder
• Comorbid diagnosis of Post-COVID-19 condition (WHO definition)
• Insufficient improvement of depressive symptoms under psychopharmacological treatment
• Stable psychopharmacological medication for at least 4 weeks prior to start of iTBS

Exclusion Criteria:

• Age <18 years or >65 years
• Pregnancy, planned pregnancy, or breastfeeding
• Legal guardianship or cognitive impairment preventing valid informed consent
• Severe developmental disorder or intellectual disability
• Acute or chronic substance abuse (alcohol, prescription drugs, or illicit drugs)
• Current treatment with benzodiazepines or Z-substances
• Acute suicidality
• Psychotic symptoms
• Severe neurological disorder (e.g., major brain injury, neurodegenerative disease)
• Ongoing treatment with another neurostimulation method (ECT, TMS, VNS)
• Contraindications to TMS, including: Intracranial metal, implants, shunts, Cochlear implant, pacemaker, implantable defibrillator, History of seizures or epileptiform EEG
• Severe general medical illness (e.g., anemia requiring transfusion, severe arrhythmias, cardiomyopathy)