McMaster-Led Study Reveals Fluvoxamine Eases Long COVID Fatigue

McMaster University Spearheads Promising Treatment for Long COVID Fatigue

A groundbreaking clinical trial co-led by researchers at McMaster University has identified fluvoxamine, a widely available antidepressant, as a potential treatment for one of the most debilitating symptoms of long COVID: persistent fatigue. This development marks a significant step forward in addressing post-COVID-19 condition (PCC), also known as long COVID, which continues to affect millions worldwide, including a substantial number of Canadians.

The study, published in the Annals of Internal Medicine, involved 399 adults in Brazil who had been experiencing fatigue for at least 90 days following a confirmed SARS-CoV-2 infection. Participants were randomly assigned to receive fluvoxamine, metformin—a diabetes medication—or a placebo for 60 days. The results showed that fluvoxamine significantly reduced fatigue severity, as measured by the Fatigue Severity Scale, outperforming placebo with a 99 percent probability. It also improved quality of life across multiple metrics. Metformin, however, did not demonstrate similar benefits.

Edward Mills, a professor in McMaster's Department of Health Research Methods, Evidence, and Impact and co-principal investigator, highlighted the importance of this finding: "This is an important step forward for patients who have been desperate for evidence-based options. Fluvoxamine showed consistent and meaningful benefits, and because it’s already widely used and well understood, it has clear potential for clinical use."

Understanding the Trial Design and McMaster's Innovative Approach

The trial employed a Bayesian adaptive design, an advanced methodology that allows for efficient evaluation of multiple treatments by stopping arms early when evidence is conclusive. This approach, championed by McMaster researchers, accelerates the path from hypothesis to actionable results. Lead author Gilmar Reis, a part-time associate professor at McMaster, noted the design's efficiency: "The trial used a sophisticated adaptive design that allowed it to reach conclusions more efficiently than traditional trials."

Fluvoxamine, marketed as Luvox, was administered at 100 milligrams twice daily. By day 60, participants on fluvoxamine reported nearly half a point lower fatigue scores compared to placebo, alongside gains in physical functioning and emotional well-being. Corresponding author Jamie Forrest from the University of British Columbia emphasized, "This trial gives clinicians their first strong evidence for a medication that helps reduce long COVID fatigue."

This builds on McMaster's renowned TOGETHER trial platform, which previously demonstrated fluvoxamine's ability to reduce hospitalization risk in acute COVID-19 patients by modulating inflammation.

Fluvoxamine's Unique Mechanism Targeting Long COVID Fatigue

Fluvoxamine is a selective serotonin reuptake inhibitor (SSRI) primarily used for obsessive-compulsive disorder and depression. Its potential in long COVID stems from its potent agonism of the sigma-1 receptor (S1R), which plays a key role in cellular stress responses, endoplasmic reticulum function, and inflammation regulation. In viral contexts like COVID-19, sigma-1 activation by fluvoxamine may mitigate cytokine storms and persistent immune dysregulation thought to underlie fatigue.

Long COVID fatigue often manifests as profound exhaustion not relieved by rest, impairing daily activities. The trial's success suggests fluvoxamine addresses underlying neuroinflammation or mitochondrial dysfunction, common hypotheses in PCC research. While the exact mechanism in established long COVID requires further study, its low cost (under $1 per day) and established safety profile make it immediately translatable.Read the full McMaster press release.

McMaster's Pivotal Role in Canada's Long COVID Research Landscape

McMaster University has been at the forefront of pandemic research, leading the TOGETHER trial that first spotlighted fluvoxamine's antiviral properties. This latest study extends that legacy to post-acute sequelae. Additionally, McMaster spearheaded Canada's first Post COVID-19 Condition (PCC) guidelines (CAN-PCC), funded by a $9 million Public Health Agency of Canada grant. These guidelines cover prevention, diagnosis, and management, recommending strategies like metformin for acute phases—though not for fatigue—and emphasizing multidisciplinary care.

The CAN-PCC collaborative involved patients, clinicians, and international experts, producing over 100 recommendations. McMaster's Department of Health Research Methods, Evidence, and Impact continues to drive evidence synthesis amid evolving data.

The Scale of Long COVID in Canada: A Public Health Challenge

In Canada, approximately 15 percent of COVID-19 survivors—potentially 2.5 million people—experience PCC symptoms beyond three months. Fatigue tops the list, affecting up to 72 percent of cases, alongside brain fog and shortness of breath. McMaster studies indicate 11 percent of infected adults face long-term effects, with seven in ten reporting daily symptoms.

This burden strains healthcare systems and economies, with lost productivity estimated in billions. Universities like McMaster are pivotal in translating global findings to Canadian contexts, where diverse populations influence symptom profiles.

Collaborative Efforts Across Canadian Universities

Beyond McMaster, institutions like the University of British Columbia host the 2026 Canadian Symposium on Long COVID, fostering national dialogue. McGill University is probing neurological underpinnings, while the University of Toronto's Rehabilitation Science Research Network advances recovery protocols. CIHR's $20 million Long COVID Web network unites these efforts, funding seed grants for innovative projects.

These hubs exemplify Canada's higher education commitment to interdisciplinary research, blending pharmacology, epidemiology, and rehabilitation.

Funding and Infrastructure Supporting Canadian Long COVID Innovation

Federal investments, including CIHR and PHAC grants, have bolstered university-led initiatives. McMaster's $9 million for CAN-PCC exemplifies this, enabling rapid guideline development. Ongoing CIHR funding supports pan-Canadian networks, prioritizing patient-centered trials. This ecosystem attracts top talent, offering research assistantships and postdocs in clinical trials.

Challenges persist, including funding gaps post-guidelines and the need for Canadian-specific trials on fluvoxamine.

Challenges and Future Directions in University-Led Research

Long COVID's heterogeneity complicates trials; adaptive designs like McMaster's offer solutions. Future studies must explore fluvoxamine's optimal dosing, subgroups benefiting most, and combinations with rehab. Canadian universities plan expanded cohorts, leveraging diverse demographics.Access the full study in Annals of Internal Medicine.

Career Opportunities in Canada's Thriving Long COVID Research Field

The surge in PCC research creates roles for faculty, postdocs, and research assistants at McMaster, UBC, and beyond. Expertise in adaptive trials, pharmacoepidemiology, and patient engagement is prized. Programs like McMaster's Health Research Methods train the next generation, positioning Canadian universities as global leaders.

Photo by Julissa Capdevilla on Unsplash

Expert Perspectives and Next Steps for Implementation

Experts urge cautious optimism: while promising, fluvoxamine requires validation in North American populations. Integration into CAN-PCC could accelerate adoption, with universities piloting protocols.