The dementia drug donepezil helped decrease fatigue in a subset of people with Long COVID, according to a study published in Frontiers in Pharmacology. In the complex study, which also included testing in mice, Japanese researchers found a majority of people with Long COVID in the cohort had reactivated human herpes virus 6 (HHV-6), which produced a specific protein (SITH-1) that they linked to symptoms of fatigue and depression.