The finding was the first verdict from a federal jury in thousands of similar cases against the company.
A federal jury found Tuesday that Monsanto’s popular weed killer Roundup was a “substantial factor” in causing a California man’s cancer, dealing a significant blow to the company as it aggressively defends its products against thousands of similar claims.
The six-member jury delivered the unanimous verdict in the United States District Court in San Francisco, months after a groundskeeper who said Roundup caused his cancer was awarded about $80 million in a separate case in California.
Tuesday’s verdict concluded the first of two phases in the federal case about the possible health risks of Roundup and whether Monsanto misled the man, Edwin Hardeman, about those risks.
Mr. Hardeman used Roundup to control weeds and poison oak on his property for 26 years. He was diagnosed with non-Hodgkin’s lymphoma in 2015.
The second phase of the case, which begins Wednesday, will focus on whether Monsanto, which was acquired by Bayer AG last year, should be held liable for partly causing Mr. Hardeman’s cancer, said his lawyer, Jennifer Moore. Ms. Moore said lawyers would seek to prove that Monsanto manipulated public opinion and science to play down Roundup’s health risks.
Lawyers will argue that Monsanto knew or should have known that Roundup causes cancer, Ms. Moore said in an interview Tuesday. Mr. Hardeman’s team will ask that the jury have the company pay his medical bills and an undetermined amount of damages, she added.
