However, federal regulators have warned against the use of hydroxychloroquine except in hospitals and formal studies, due to the the risk of side effects, especially heart rhythm problems.Boulware’s study included 821 people in the United States and Canada living with someone who was diagnosed with COVID-19 or who was at high risk of getting it due to their job, such as doctors, nurses and ambulance workers who had significant exposure to a sick patient while not wearing their full protective gear.The participants were randomly assigned to take either the nutrient folate as a placebo or hydroxychloroquine for five days, beginning within four days of their exposure.After 14 days, 12 percent who were on the drug developed symptoms consistent with COVID-19, versus 14 percent in the placebo group.Boulware says the difference was so small, it could have occurred simply by chance.The results were not any different among another group who were taking zinc or vitamin C, which some people believed could help hydroxychloroquine fight the coronavirus. A malaria drug that President Trump reportedly took in an effort to prevent the coronavirus has proven ineffective against the disease in a study.Results of that study, published Wednesday in the New England Journal of Medicine, show that hydroxychloroquine is no better than placebo pills keeping the virus at bay.However, the drug also does not seem to cause serious harm. About 40 percent of people taking it for the study had side effects, mostly mild stomach problems.“We were disappointed. We would have liked for this to work,” said the study leader, Dr. David Boulware, an infectious disease specialist at the University of Minnesota. “But our objective was to answer the question and to conduct a high-quality study,” because the evidence on the drug so far has been inconclusive, he said.Hydroxychloroquine has long been used to treat malaria, lupus and rheumatoid arthritis.Trump recently took a two-week course of the drug, along with zinc and Vitamin D, after two White House staff members tested positive for COVID-19. The president had no effects from the course, according to the results of his latest physical, which were released by his doctor Wednesday.