Age: 7 - 18
Healthy Volunteers: Not accepted
Inclusion Criteria:
1. Age 7-18 years
2. Resident of British Columbia
3. DSM-5 diagnosis of OCD based on (a) history of prior clinician assessment and (b) standardized interview
4. CY-BOCS score ≥16 (moderate to severe)
5. Able to take medication twice daily in capsule form (in whole form or sprinkled contents)
6. Negative pregnancy test (either serum or urine) in participants with child-bearing potential
7. Use of highly effective and/or double barrier contraception, or abstinence, in participants with child-bearing potential
Exclusion Criteria:
1. Lifetime diagnosis of renal disease, liver disease, gastrointestinal bleeding, peptic ulcer disease, inflammatory bowel disease, severe or uncontrolled asthma, bleeding disorders, heart disease, heart failure, or hypertension
2. Current major depressive episode, acute psychosis, active substance use, suicidality, or restriction of fluid intake
3. Pregnant or breastfeeding during the study period
4. Active infection or antibiotic treatment at baseline
5. Allergy to celecoxib, sulfonamide compounds, or NSAIDs, including aspirin
6. Current or previous regular use of immune-modulating therapies for treatment of OCD symptoms, at an effective anti-inflammatory dose (including NSAIDs, corticosteroids, or biologics)
7. Use of NSAIDs at any dose at a frequency ≥ 3 times per week during the 2 months prior to randomization
8. Current use of intravenous or oral corticosteroids
9. Concurrent use of CYP2C9 inhibitors fluconazole, amiodarone, oxandrolone or methotrexate; CYP2C9 inducers including rifampin and phenobarbital; or any other drug that may interact with celecoxib and, in the opinion of Dr. Stewart or another study investigator, represents a potential safety risk
10. Poor CYP2C9 metabolizer (i.e. CYP2C9\*3/\*3 genotype) based on clinical suspicion or previous genotyping.
11. Abnormality identified on baseline serology including leukocytosis, leukopenia, thrombocytopenia, anemia, abnormal renal function (Cr > 1.5 x upper limit of normal), or abnormal liver function (ALT, ALP, or AST > 1.5x upper limit of normal)
12. New psychotropic medication (i.e. medication with known or potential impact on psychiatric symptoms, including selective serotonin reuptake inhibitors, benzodiazepines, antipsychotics, stimulants, anticonvulsants, mood stabilizers, or other medications) or other ongoing regular medication started in the 10 weeks prior to baseline, or change in dose in the 4 weeks prior to baseline
13. Changes in CBT or other psychotherapy in the 4 weeks prior to baseline (i.e. change in regular frequency, modality, or care provider)
14. Notable other treatment changes during the study period (either pharmacotherapy or psychotherapy)
15. No regular physician (family doctor or specialist) providing usual medical care
16. Participant/parents unable to provide informed consent or assent or participate in self-care, AE reporting, or follow-up assessments
17. Inability to have blood pressure measured within 2 months prior to enrollment (either on-site at BCCH or by a primary care provider).
18. Intention of pregnancy in participants with child-bearing potential.