GSK shares in London tumbled the most in nearly two years after a Delaware judge allowed jury trials to proceed in cases concerning the discontinued heartburn drug Zantac, which is allegedly linked to cancer.
On Friday, Judge Vivian Medinilla of the Delaware Superior Court in Wilmington agreed that plaintiffs' scientific evidence could be heard in jury trials.
"It would be improper to simply dismiss these experts as 'poseurs or witnesses for hire,'" Medinilla said, adding that each side's arguments should be decided by juries.
She continued, "Delaware courts are loath to step into the heart of the technical debate between opposing scientists."
On Saturday, Brent Wisner, one of the plaintiffs' lead lawyers, was quoted by Reuters as saying, "This moves us one step closer to justice for our clients."
Sanofi has said it faces about 25,000 lawsuits in Delaware, much lower than GSK's 70,000 lawsuits over Zantac.
In response to Medinilla's court ruling, GSK said it will appeal the decision.
"Following the 16 epidemiological studies looking at human data regarding the use of ranitidine, the scientific consensus is that there is no consistent or reliable evidence that ranitidine increases the risk of any cancer," GSK said.
GSK shares plunged 10% in London, the most since Aug. 11, 2022, when the fears of Zantac litigation spooked Wall Street.
Most of the year's gains have been wiped out.
Citi analyst Peter Verdult told clients that GSK's settlement would cost around $3 billion. JPMorgan analysts see $2 billion to $3 billion.
