As the role of (neuro)inflammation in depression is emerging, augmentation of antidepressant treatments with anti-inflammatory drugs such as celecoxib has shown encouraging preliminary results. However, inflammation is not present in all depressed patients. Depression is heterogeneous: patients express diverse and sometimes opposing symptoms and biological profiles. The investigators of the present trial recently introduced the concept of ImmunoMetabolic Depression (IMD), characterized by the clustering of inflammatory/metabolic dysregulations and atypical, energy-related symptoms (hyperphagia, weight gain, hypersomnia, fatigue and leaden paralysis), and present in approximately 30% of cases. Converging evidence suggests that in this subgroup of depression cases, inflammation may exert a crucial pathobiological mechanism, representing therefore an actionable therapeutic target. In this trial IMD will be applied as a tool to personalize treatment, by matching depressed subjects with IMD with a targeted anti-inflammatory add-on treatment.

In this study, 140 persons with IMD will be selected. In this specific group of patients, the investigators will test whether celecoxib add-on (400 mg/d) is more effective than placebo in the treatment of depression through a 12-week double-blind, randomized (1:1), placebo-controlled trial. By selecting specifically depressed patients with IMD, the proposed treatment selectively targets key inflammatory pathophysiological pathways to enhance clinical outcome for depression. This personalized approach is expected to lead to large health gains for a sizable proportion of patients. The main hypothesis is that the group of patients with IMD receiving TAU + celecoxib, as compared to the TAU + placebo, will show a better symptom course over the 12-week follow-up.

Rationale: Depression is a major driver of disability and related health-care costs. Available treatment options are far from optimal, with only ~60% response. Developing effective treatments requires new treatment targets to depression pathophysiology. As the role of (neuro)inflammation in depression is emerging, augmentation of antidepressant treatments with anti-inflammatory drugs such as celecoxib has shown encouraging preliminary results. However, inflammation is not present in all depressed patients. Depression is heterogeneous: patients express diverse and sometimes opposing symptoms and biological profiles. The investigators of the present study recently introduced the concept of ImmunoMetabolic Depression (IMD), characterized by the clustering of inflammatory/metabolic dysregulations and atypical, energy-related symptoms (hyperphagia, weight gain, hypersomnia, fatigue and leaden paralysis), and present in 30% of cases. Converging evidence suggests that in this subgroup of depression cases, inflammation may exert a crucial pathobiological mechanism, representing therefore an actionable therapeutic target. In this study IMD will be applied as a tool to personalize treatment, by matching depressed subjects with IMD with a targeted anti-inflammatory add-on treatment. The underlying hypothesis is that this personalized intervention in subjects with IMD, through a reduction of inflammation, lowers depressive symptoms and associated physical fatigue, while increasing functioning compared to placebo.

Objective: Among patients under treatment for depression, 140 persons with IMD will be selected. In this specific group of patients, the investigators will test whether celecoxib add-on (400 mg/d) is more effective than placebo in the treatment of depression through a 12-week double-blind, randomized (1:1), placebo-controlled trial.

Study design:12-week double-blind placebo-controlled randomized clinical trial Study population: 140 persons with major depressive disorder (DMS-5) with atypical, energy-related symptoms (≥6 on IDS atypical, energy-related symptoms) AND low-grade inflammation (CRP>1mg/L) (e.g. ImmunoMetabolic Depression), and under treatment with SSRI or SNRIs.

Intervention: celecoxib add-on (400 mg/d) vs placebo Main study parameters/endpoints: Primary outcome parameter is the difference in trajectories of depression symptoms, as measured with the 30-item Inventory of Depressive Symptomatology - self-report during follow-up. Secondary outcome parameters include amongst others, response on the IDS, remission, anxiety, fatigue, food craving, sleep and adverse side events.

Inclusion Criteria:

• DSM-5 diagnosis of MDD confirmed with clinical interview (MINI-S voor DSM-5 Nederlandse versie 2019)
• Currently using pharmacotherapy (e.g., SSRI, SNRI, TCA, TetraCA, MAOI, other antidepressant [bupropion, vortioxetine, agomelatine])) and/or psychotherapy. Subjects should be on the current treatment for at least 4 weeks
• IDS-SR score ≥26 (moderate to severe depressive symptoms) and a score ≥6 on atypical, energy-related symptoms scale from IDS
• CRP > 1mg/L
• A female participant is eligible to participate if she is not pregnant or breastfeeding, and one of the following conditions applies: 1) is not a woman of child bearing potential (WOCBP); 2) Is a WOCBP and agrees to use, or is already using, a contraceptive method during the intervention period and up to 1 month after the intervention
• Signed informed consent

Exclusion Criteria:

• Contraindications for celecoxib (history of: peptic ulcers, gastrointestinal bleeding, ischemic heart disease, stroke, heart failure, allergic reactions to aspirin/NSAIDs/coxibs; impaired kidney function (creatinine clearance < 30 ml/min), impaired liver function (ALT > 2x ULT)
• ECT in the past 3 months
• Being on other psychotropic drugs
• Clinically overt alcohol/drug dependence or other primary psychiatric diagnoses (schizophrenia, schizoaffective, OCD, or bipolar disorder)
• Chronic use of anti-inflammatory drugs and corticosteroids
• Current use of anticoagulants
• Not speaking Dutch

Individual data collected during the study of participants explicitly agreeing on this possibility trough written informed consent; data will be de-identified

Immediately following study closure and publication of the main results, no end date.

Investigators whose proposed use of the data has been approved by an independent review committee identified for this purpose