Adjunct Minocyline in Treatment-resistant Depression

Inclusion Criteria: * Informed consent * male or female * between age 18 and 75 * BMI between 18 and 40 inclusive * Non-lactating, non-pregnant females of child-bearing potential must be willing to use an effective contraceptive method * All participants must fulfil diagnostic criteria of moderate or severe MDD according to the DSM-5. * HAMD-17 score of at least 16 points at baseline and a * CGI-S score of at least 4. * AD-ST must have been administered at a sufficient dose for at least 6 weeks in the current episode and at a * stable regimen for at least 14 days prior to baseline. * Dose and duration of AD-ST must be verifiable Exclusion Criteria: * prevalence of neurodegenerative disorder * prevalence of any neurological disorder that caused the depressive symptoms * prevalence of any severe, unstable general medical condition, including chronic inflammatory disease such as rheumatoid arthritis or inflammatory bowel disease * prevalence of any other psychiatric disorder that better explains the presence of depressive symptoms * Improvement by more than 50% in HAMD-17 score during the last 14 days prior to baseline * pregnant or nursing women will not be allowed. * substance or alcohol abuse within past 6 months or positive urine drug screening * abnormal thyroid function (euthyroid at presentation), liver or kidney dysfunction * history of autoimmune disease (except Hashimotos thyroiditis) * clinically significant laboratory abnormalities (outside normal ranges) * current medication with anti-inflammatory substances (NSAIDs, corticosteroids)