Lithium Long COVID Dose-finding Study

Inclusion Criteria: 1. Enrolled from November 2022-July 2023 in lithium long COVID clinical trial at UB. 2. Reports bothersome fatigue and/or brain fog while not taking lithium or, reports satisfactory benefit to these symptoms while taking lithium. 3. Fatigue Severity Scale (FSS) score ≥28 or Brain Fog Severity Scale (BFSS) score ≥28 at baseline or; FSS \<28, BFSS \<28 and PGIC at Visit 1 of "much improved" or "very much improved" while taking lithium. 4. Did not "respond" to placebo therapy, based on the responder analyses outlined in the Preliminary data section above, defined as a ≥18-point reduction FSS or ≥15-point reduction in BFSS from baseline to the end-of-double-blind study phase while receiving placebo therapy. Exclusion Criteria: 1. Fever or signs of acute infection in last 4 weeks. 2. COVID vaccine administered within 4 weeks. No change in any psychoactive or steroid medications for ≥30 days. 3. Plan to change a psychoactive, steroid or diuretic medication in next 5 weeks. 4. History of heart attack or stroke within the previous year. 5. Active medical, psychiatric or social problem that would interfere with completing the study procedures in the opinion of the investigator. 6. Daily NSAID use. 7. Pregnant or nursing or planning to get pregnant over the next 11 weeks.