Patients with Post-COVID Fatigue Syndrome (PCFS) have profound and persistent fatigue along with other symptoms (brain fog, etc.). Naltrexone is a medication that attaches to opioid receptors and blocks the effects of opioid drugs. Low Dose Naltrexone (LDN), which is about 1/10th of a normal dose, has been used with some success in similar conditions. This study aims to determine if LDN reduces fatigue and improves related symptoms of PCFS.

The main study tasks will involve the following: • Taking LDN or a placebo (an inactive substance) for 16 weeks • Virtual or in-person study visits and check-ins with the study team • Completion of questionnaires • Wearing a pedometer (step counter) for one week, twice during the trial period • Collecting blood samples • In-person visit assessments (optional) • Completion of a short study drug diary daily for the first 4 weeks