Long COVID, also referred to as post-acute sequela of COVID-19 (PASC), is present in asubstantial number of individuals, and treatment for this is warranted. Two differenthypothetical models of Long COVID suggest attenuated mitochondrial energy production andfunctional brain alterations associated with psychosocial load, respectively, to be keymechanisms in the underlying pathophysiology. Given the potential importance of metabolicdisturbances, dietary supplement by Nicotinamide Riboside (NR, sales name Niagen®) may bebeneficial. Given the potential importance of functional brain alterations, a tailoredand personalized Mind-Body Reprocessing Therapy (MBRT) may be beneficial. The MBRTconsists of 4 to 6 face-to-face therapist encounters in combination with digitalresources.The primary objective is to determine whether NR 1000 mg twice daily and/or MBRT increasehealth-related quality of life in individuals with Long COVID compared with care as usualand/or placebo. The Medical Outcome Study 36-item short form (SF-36), general healthsubscore is the primary endpoint. Secondary endpoints are: Markers of inflammation(hsCRP) and cognitive function (trail making test), cost-effectiveness, and thepatient-reported symptoms fatigue, dyspnoea, and global impression of change in symptoms,function and quality of life. Explorative objectives encompass intervention effects onadditional cognitive function markers, biological markers (indices of inflammation andautonomic nervous activity), disability markers (work attendance) and patient symptoms,as well as the exploration of long-term effects, differential subgroup effects,intervention effect mediators and intervention effect predictors.The study is a randomized controlled trial featuring a 2 x 2 factorial design where MBRTis compared with usual care and NR is compared with placebo. The latter comparison isdouble blinded. Eligible participants are individuals (18-70 years) with confirmed LongCOVID interferring negatively with daily activities. A total of 310 participants will beenrolled. After baseline assessment (T1), the participants will be randomized 1:1 forboth treatment comparisons, resulting in four treatment groups: a) MBRT and NR; b) usualcare and NR; c) MBRT and placebo; d) usual care and placebo. All treatment periods lastfor three months, followed by primary endpoint assessment (T2). Total follow-up time is12 months (T3). A comprehensive investigational program at all time points includesclinical examination, functional testing (spirometry, autonomic cardiovascular control,neurocognitive functions), sampling of biological specimens (blood) and questionnairecharting (background/demographics, clinical symptoms, psychosocial factors, studyevents).