Inclusion Criteria:
* Post COVID according to WHO criteria and verified by post COVID physician
* Post-exertional malaise (PEM) according to DSQ-PEM questionnaire
* Bell's disability score 20-70%
* Mild initial SARS-CoV-2 infection (no hospitalisation)
* WHO performance score of 0 before initial SARS-CoV-2 infection
Exclusion Criteria:
* Patients at risk for cardiac conduction disorders
* History of clinical significant gastro-intestinal surgery or dysmotility that impairs the adsorption of the IMP
* Clinically significant respiratory or cardiovascular disease
* Unstable neurological disease
* Clinically significant active psychiatric disorder that requires treatment
* History of substance abuse
* Active malignancy within the past 5 years
* History of solid organ transplantation
* Active HIV, hepatitis B or C infection
* BMI \< 18.5 or \> 35
* Pregnancy or breastfeeding
* Clinically relevant laboratory test value outside the reference range
* Use of the following medication, unless stable for at least one month before study and remaining stable throughout the study: (multi)vitamins, co-enzyme Q10, Vitamin E, riboflavin, amino acids, antioxidant supplements and any medication negatively influencing mitochondrial functioning (including but not limited to valproic acid, glitazones, statins, antivirals, amiodarone and NSAIDs)
* Use of the following medication: any moderate or strong Cytochrome P450 (CYP)3A4 inhibitors (all 'conazoles-anti-fungals', HIV antivirals, grapefruit), strong CYP3A4 inducers ((including HIV antivirals, carbamazepine, phenobarbital, phenytoin, rifampicin, St. John's wort, pioglitazone, troglitazone) or any medication metabolized by CYP3A4 with a narrow therapeutic index, medication known to be substrate of Organic Cation Transporter 1 (OCT1) and organic cation transporter 2 (OCT2) or strong P-glycoprotein inhibitors (including amiodarone, azithromycin, captopril, clarithromycin, cyclosporine, piperine, quercetin, quinidine, quinine, reserpine, ritonavir, tariquidar, and verapamil).
* Use of any medication known to affect cardiac repolarization unless QTc interval at screening is normal during stable treatment for a period of two weeks, or 5 half-lives
