A California judge on Thursday reduced a $2 billion US jury verdict, slashing the award for a couple who blamed Bayer AG's glyphosate-based weed killer Roundup for their cancer to $86.7 million US.

Superior Court Judge Winifred Smith of the California Superior Court in Oakland said the jury's billion-dollar punitive damages award was excessive and unconstitutional, but rejected Bayer's request to strike the punitive award outright.

Under Smith's final order, California couple Alva and Alberta Pilliod would receive roughly $17 million US in compensatory damages and $69 million US in punitive damages, down from $55 million US and $2 billion US, respectively.

The plaintiffs still have to formally accept the reduced award.

In a statement Thursday, Bayer said Smith's decision to slash the award was a step in the right direction, but added it would file an appeal.

"We continue to believe that the verdict and damage awards are not supported by the evidence at trial and conflict with the extensive body of reliable science and conclusions of leading health regulators worldwide that confirms glyphosate-based herbicides can be used safely and that glyphosate is not carcinogenic," the company said.

Bayer under siege

Bayer faces Roundup cancer lawsuits by more than 13,400 plaintiffs across the United States. The Germany-based company bought Roundup-maker Monsanto in a $63 billion US deal last year, but has since seen its share price tumble over the glyphosate litigation.

Plaintiffs allege Roundup causes non-Hodgkin's lymphoma and that Monsanto has for decades tried to influence scientists and regulators to bury cancer evidence. Bayer denies those allegations.

The company had asked Smith to strike the punitive damages award in the Pilliods' case, arguing that hundreds of studies and assessments by regulators worldwide concluded the herbicide to be safe for human use.

But the judge in her Thursday order rejected those arguments.

"In this case there was clear and convincing evidence that Monsanto made efforts to impede, discourage, or distort scientific inquiry and the resulting science," Smith said.

To date, Bayer has lost three U.S. jury trials in the Roundup litigation, with juries in California awarding multi-million dollar awards. The company is appealing the decisions.

In August, Bayer is scheduled to face its first trial outside California at a courthouse in St. Louis, Mo. Monsanto has recruited Missouri-based expert witnesses to make its case in a place where it has century-old roots, but where juries often hit companies with huge damages.