University of Minnesota Trial Shows Hydroxychloroquine Does Not Prevent COVID-19 in High-Risk Health Care Workers

First randomized clinical trial to evaluate hydroxychloroquine as pre-exposure prophylaxis in health care workers

MINNEAPOLIS, MN-October 21, 2020 – University of Minnesota Medical School physician researchers studied hydroxychloroquine as a treatment to prevent COVID-19 for those with high-risk for exposure to the virus – health care workers. 

The pre-exposure prophylaxis trial results, which were published in Clinical Infectious Diseases, determined that taking 400mg of hydroxychloroquine once or twice weekly did not prevent the development of COVID-19 in health care workers better than the placebo.

“This randomized placebo-controlled trial launched on April 6, with the objective of evaluating whether or not hydroxychloroquine taken once or twice weekly in health care workers at high risk for COVID-19 exposure could prevent COVID-19 infection,” said principal investigator Radha Rajasingham, MD, an infectious diseases physician and researcher at the U of M Medical School.

The double-blind trial enrolled 1,483 health care workers and first responders from across the U.S. and Canada. Participants were randomly assigned to receive once-weekly hydroxychloroquine, twice-weekly hydroxychloroquine or placebo. Participants were followed for a minimum of four weeks and up to twelve weeks to evaluate who developed COVID-19. 

Overall, 7.9% assigned the placebo developed COVID-19, while 5.9% assigned hydroxychloroquine developed COVID-19. Those results were not statistically significant, meaning there was not a meaningful difference between hydroxychloroquine and the placebo. Side effects were reported in 21% of participants assigned the placebo; 31% in the once-weekly hydroxychloroquine group and 36% in the twice-weekly hydroxychloroquine group. The most common side effects were nausea, upset stomach and diarrhea. There was no increased risk of serious side effects or cardiac complications from taking hydroxychloroquine compared to the placebo.

The research team from the University of Minnesota included David Boulware, MD, MPH; Sarah Lofgren, MD; Caleb Skipper, MD; and Matthew Pullen, MD, from the U of M Medical School; statisticians Ananta Bangdiwala, Nicole Engen and Kathy Hullsiek, PhD, from the U of M School of Public Health, Melanie Nicol, PharmD, PhD, from the U of M College of Pharmacy, among many students and trainees. The study was in collaboration with colleagues at Vanderbilt University and Oregon Health & Science University. 


About the University of Minnesota Medical School
The University of Minnesota Medical School is at the forefront of learning and discovery, transforming medical care and educating the next generation of physicians. Our graduates and faculty produce high-impact biomedical research and advance the practice of medicine. Visit to learn how the University of Minnesota is innovating all aspects of medicine.

For media requests, contact:

Kelly Glynn
Media Relations Coordinator
University of Minnesota Medical School