Abstract

INTRODUCTION

A significant proportion of individuals suffering from post COVID-19 condition (PCC, also known as long COVID) can present with persistent, disabling fatigue similar to myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and post-viral fatigue syndromes. There remains no clear pharmacological therapy for patients with this subtype of PCC, which can be referred to as post-COVID fatigue syndrome (PCFS). A low dose of the opioid antagonist naltrexone (ie, low-dose naltrexone (LDN)) has emerged as an off-label treatment for treating fatigue and other symptoms in PCC. However, only small, non-controlled studies have assessed LDN in PCC, so randomised trials are urgently required.

METHODS AND ANALYSIS

A prospective, randomised, double-blind, parallel arm, placebo-controlled phase II trial will be performed to assess the efficacy of LDN for improving fatigue in PCFS. The trial will be decentralised and open to eligible individuals throughout the Canadian province of British Columbia (BC). Participants will be recruited through the province-wide Post-COVID-19 Interdisciplinary Clinical Care Network (PC-ICCN) and research volunteer platform (REACH BC). Eligible participants will be 19-69 years old, have had a confirmed or physician-suspected SARS-CoV-2 infection at least 3 months prior and meet clinical criteria for PCFS adapted from the Institute of Medicine ME/CFS criteria. Individuals who are taking opioid medications, have a history of ME/CFS prior to COVID-19 or history of significant liver disease will be excluded. Participants will be randomised to an LDN intervention arm (n=80) or placebo arm (n=80). Participants in each arm will be prescribed identical capsules starting at 1 mg daily and follow a prespecified schedule for up-titration to 4.5 mg daily or the maximum tolerated dose. The trial will be conducted over 16 weeks, with assessments at baseline, 6, 12 and 16 weeks. The primary outcome will be fatigue severity at 16 weeks evaluated by the Fatigue Severity Scale. Secondary outcomes will include pain Visual Analogue Scale score, overall symptom severity as measured by the Patient Phenotyping Questionnaire Short Form, 7-day step count and health-related quality of life measured by the EuroQol 5-Dimension questionnaire.

ETHICS AND DISSEMINATION

The trial has been authorised by Health Canada and approved by The University of British Columbia/Children's and Women's Health Centre of British Columbia Research Ethics Board. On completion, findings will be disseminated to patients, caregivers and clinicians through engagement activities within existing PCC and ME/CFS networks. Results will be published in academic journals and presented at conferences.

TRIAL REGISTRATION NUMBER

NCT05430152.

MeSH

Infections, Fatigue Syndrome, Chronic, Therapeutics, History, Quality Of Life, Naltrexone, Post-Acute Covid-19 Syndrome

Cited by

• A Narrative Review of the Efficacy of Long COVID Interventions on Brain Fog, Processing Speed, and Other Related Cognitive Outcomes. Biomedicines, 2025
• Naltrexone dose-selectively modulates goal-directed behavior and the hypothalamic proteome in rats. Pharmacol Rep, 2025
• Low-dose naltrexone use for the management of post-acute sequelae of COVID-19. Int Immunopharmacol, 2023
• Multidisciplinary collaborative guidance on the assessment and treatment of patients with Long COVID: A compendium statement. PM R, 2025
• Longitudinal analysis and treatment of neuropsychiatric symptoms in post-acute sequelae of COVID-19. J Neurol, 2023
• Transforming Niclosamide through Nanotechnology: A Promising Approach for Long COVID Management. Small, 2025