Diclofenac Dose Response Study

Inclusion Criteria: * Age 21-65 * Meet DSM-5 diagnostic criteria for current AUD of any severity (Mild, Moderate, or Severe) * In the 30-day period before enrollment, consume \> 14 and \> 7 standard drinks per week for men and women, respectively * In the 30-day period before enrollment, engage in heavy drinking (5 or more drinks for men, 4 or more drinks for women) ≥ 5 times per month Exclusion Criteria: * Currently in treatment, a history of treatment within the 30 days before enrollment, or currently seeking immediate treatment for AUD * Current (last 12 months) DSM-5 diagnosis of SUD for any psychoactive substances other than alcohol, nicotine, and cannabis (cannabis use disorder, mild severity allowed; moderate and severe excluded) * Currently prescribed a psychotropic medication for the treatment of schizophrenia spectrum and other psychotic disorders, bipolar and related disorders * Lifetime DSM-5 diagnosis of schizophrenia spectrum and other psychotic disorders and bipolar and related disorders * Positive urine toxicology screen for the following substances: cocaine, opiates, amphetamines, methamphetamine, phencyclidine, barbiturates, benzodiazepine, methadone, and tricyclic antidepressants * Self-reported current daily use of opioids (including prescribed) * If female: pregnant, nursing, or with reproductive potential who refuses to use reliable methods of birth control throughout the study * Serious alcohol withdrawal symptoms as indicated by a score ≥ 10 on the Clinical Institute Withdrawal Assessment for Alcohol-Revised * Any autoimmune disorder, inflammatory disorder, hypercoagulable state, cardiovascular disease or other medical condition (e.g., any cardiac, renal, or liver disease, uncontrolled hypertension, or diabetes) that may interfere with safe study participation and/or study aims. Specific examples of exclusionary medical conditions include but are not limited to: 1. Any lifetime history of 1) serious GI conditions, including ulcer disease, gastrointestinal bleeding, and clinically significant gastritis, or, 2) serious cardiovascular conditions, including heart failure, myocardial infarction, stroke, pulmonary embolism, blood clots, deep vein thrombosis, or clotting disorder, 3) liver disease or impaired liver function, and 4) renal disease or insufficiency 2. Current uncontrolled hypertension 3. AST and ALT \> four times the upper limit of the normal range, or albumin, GFR, BUN, or creatinine 15% \> the upper limit of the normal range 4. Clinically significant ECG findings, including clinically significant arrhythmia, atrioventricular block, prolonged QTc interval, or enlarged or hypertrophic heart 5. Serious brain conditions, including epilepsy, dementia and neurodegenerative diseases, traumatic brain injury (TBI), etc. TBI exclusionary criteria include: suffered a mild or moderate TBI within the last 12 months, a severe TBI at any point in their life, or a moderate TBI before the age of 12 * Attempted suicide in the past 3 years and/or serious suicidal intention or plan within the past year * Currently on prescription medication that contraindicates use of diclofenac, including but not necessarily limited to: oral corticosteroids, anticoagulants, lithium, warfarin, aspirin (daily use), methotrexate, cyclosporine, ACE-inhibitors, diuretics like furosemide and thiazides, and any medication that significantly influences CYP2C9 enzyme activity (e.g., rifampin, voriconazole). * Previously known hypersensitivity, including gastroenteritis, asthma, and allergic-type reactions, to any NSAID and/or aspirin * Current daily use of any NSAID or regular pattern of near daily use within the past three months, regular use of a prebiotic or probiotic supplement and/or any antibiotic, prebiotic, or probiotic use within the last month * Any other circumstances that, in the opinion of the investigators, compromises participant safety, ability of the investigators to conduct the study as designed, and/or study integrity * Current or recent (within 3 months) participation in a clinical trial involving medication administration * Has below a 6th grade reading level * Within the last 3 months, tested positive for COVID-19 (i.e. the SARS-CoV-2 virus) and experienced common related symptoms