Bipolar disorder is a leading cause of disability worldwide. A high proportion of patients with bipolar disorder experience persistent depressive symptoms that do not respond to standard drug treatments. Recent evidence has suggested that anti-inflammatory treatment may reduce depressive symptoms. Minocycline is a tetracycline antibiotic with good central nervous system (CNS) penetration that has been suggested to be effective as an adjunct drug in improving depressive symptoms. Celecoxib, a selective cyclooxygenase 2 (COX-2) inhibitor, has also shown promising results in the treatment of depressive symptoms. In this factorial design, double blind, randomised controlled trial the investigators will determine the efficacy of minocycline and/or celecoxib as an adjunct to treatment as usual (TAU) in patients experiencing a depressive phase of bipolar I or II disorder. The investigators hypothesise that augmentation with minocycline and/or celecoxib will lead to an improvement in depressive symptoms in participants in comparison with placebo.