A US jury ordered Takeda Pharmaceutical to pay $6 billion in damages over claims that it concealed cancer risks associated with its Actos diabetes drug, the plaintiffs' lawyer said on Tuesday.

The massive award was met with "stunned silence" in the packed Lafayette, Louisiana, courtroom, plaintiffs' lawyer Mark Lanier said.

Eli Lilly and Co, Takeda's co-defendant, was ordered to pay $3 billion in punitive damages.

Takeda, Japan's largest pharmaceutical company, said it disagreed with the verdict and would challenge it vigorously, including through post-trial motions and an appeal.

Takeda's shares fell as much as 8.8 percent to 4,396 yen after the verdict, hitting an eight-month low and marking their biggest one-day drop in five years.

Lanier acknowledged it was not certain whether the damages award would be sustained as the legal process continued.

"Nobody has gone out and bought a new home," he told Reuters. "This is a conservative judge and a conservative court and she's very 'balls and strikes'. We're not under any grand illusion."

He added that the judge wanted post-verdict motions filed quickly but had set no precise schedule.

Last May, a US judge had nullified a separate jury verdict for $6.5 million against Takeda after ruling that the plaintiffs had failed to offer any reliable evidence that Actos had caused cancer.

In the latest case, Lanier said the jury deliberated for only an hour and 10 minutes to deliver its verdict finding liability on all 14 questions, and another 45 minutes to come out with the multibillion dollar punitive damages.

The jury also ordered the payment of $1.475 million in compensatory damages in the suit.

Actos (Pioglitazone HCl) is marketed under a variety of names, including Actos, Actoplus Met, and Duetact.

Actos has been Takeda most successful product – representing more than 25 per cent of Takeda’s total revenue and with global sales of nearly $5 billion in 2010 ($3.78 billion in the US).

Despite Actos’ popularity and success, studies have now confirmed that Actos greatly increases the risk for bladder cancer.  According to a French study, a cumulative dose of greater than 28,000 milligrams and an exposure of longer than one year led to a substantial increase in bladder cancer, particularly in men.

The French Medicines Agency this summer suspended use of Actos while the European Union’s European Medicines Agency completed a risk/benefit analysis of the drug. In late July, the EMA confirmed an increased risk of bladder cancer, but determined that the benefit of Actos outweighed the risk for some patients and mandated a three- to six-month review of each individual patient.

In June 2011, the FDA released an Actos bladder cancer warning. The FDA’s new warning came on the heels of an interim analysis of an epidemiological study conducted by Takeda, the Japanese pharmaceutical company that manufactures Actos. - Reuters and other agencies