The drug was seen as a possible treatment for the coronavirus.
The Chinese trial showed remdesivir didn't improve patients’ condition or reduce the pathogen’s presence in the bloodstream, according to the Financial Times, which cited draft documents published accidentally by the World Health Organization.
Gilead, which was one of the biggest losers on the Nasdaq, warned that the post included “inappropriate characterizations of the study,” and added that "the study results are inconclusive, though trends in the data suggest a potential benefit for remdesivir, particularly among patients treated early in disease."
The Dow Jones Industrial Average, up 400 points, or more than 1.7%, at its high during the session, ended up 39 points, or 0.17%, at 23,515, while the S&P 500 ended down 0.05% and the Nasdaq was off 0.01%.
Stocks were higher earlier in the session after oil prices jumped and the number of Americans seeking unemployment benefits for the first time rose by 4.4 million last week but were slightly less than expected.
The U.S. Labor Department reported that 4,427,00 Americans filed for unemployment benefits in the week ended April 18, compared with the 4.25 million in claims expected by analysts polled by FactSet. The five-week total now stands at more than 26 million. Continuing jobless claims - a rolling number - came in at 15.976 million.
“This is another terrible week for layoffs. One of the concerns is that the government support doesn’t seem to be stemming the tide here," said James McCann, senior global economist at Aberdeen Standard Investments.
"The scale of joblessness in the U.S. is clearly larger than other economies. This is partly due to the flexibility of the labour market, but also indicative of the problems the U.S. has had ensuring that firms hold onto their workers in the way other countries have through wage subsidies,” McCann added.
The Treasury Department updated its guidance Thursday and asked publicly traded companies to repay loans they received this month under the Paycheck Protection Program, which are intended to aid small businesses hurt by the coronavirus pandemic.
The department said it was “unlikely that a public company with substantial market value and access to capital markets” would be able to show that the money would be needed to support its ongoing business. About 150 public companies have received nearly $600 million in loans, according to the Wall Street Journal.
Oil prices rose Thursday for a second straight day, sparked by President Donald Trump's instruction for the U.S. Navy to "shoot down" any Iranian gunboats that harass American ships at sea.
Iran on Thursday vowed a "crushing response" to threats from Trump as tensions in the Gulf region escalated.
West Texas Intermediate crude oil, the U.S. benchmark, rose 23.6% to $17.03 a barrel.
The House of Representatives, meanwhile, is expected Thursday to approve and then send to Trump a nearly $500 billion aid measure for businesses crippled by the coronavirus.
The latest aid package would bring the total cost of the bills designed to cushion the blow from the coronavirus pandemic to about $2.5 trillion, according to the Congressional Budget Office.