This study examines the antidepressant efficacy of minocycline as an adjunct to an antidepressant standard treatment (AD-ST), for patients with unipolar major depressive disorder (MDD).

This is a double-blind, placebo-controlled, randomized, multicenter proof-of-principle trial of adjunctive minocycline for patients with unipolar major depressive disorder (MDD). The study tests the antidepressant efficacy of minocycline as an adjunct to an antidepressant standard treatment (AD-ST), for patients with unipolar major depressive disorder (MDD). The respective AD, for which non-response has been documented, must be on a stable regimen for at least 14 days prior to inclusion. AD-ST will then be continued throughout the trial. Trial medication is adjunct oral minocycline 200 mg/day or placebo. Response to treatment will be measured via the Montgomery-Asberg Depression Rating Scale (MADRS). The total study duration for each patient will be 6 weeks.

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)