Hardeman has alleged that his use of Roundup caused him to develop non-Hodgkin lymphoma (NHL). He used Roundup from the 1980s to 2012 to weed large amounts of Roundup to clear his 22-hectare property in Sonoma north of San Francisco. In 2015, he was diagnosed with non-Hodgkin's lymphoma. His case is considered a “bellwether” trial for hundreds of similar cases joined in Roundup Products Liability Litigation (MDL) (3:16-md-02741-VC). The judge decided that the trial should take place in 2 phases. It will first have to be demonstrated that Roundup caused Hardeman's disease, and only if the answer is yes, it will be possible to judge whether Monsanto (acquired by Bayer in 2018) has acted with malice and/or withheld information. The jury, composed of 6 persons, must be unanimous for Hardeman to win his case.

The hearings began on February 25, and ended on March 12. After 5 days of deliberation, the jurors unanimously answered yes to the question: Did Mr. Hardeman prove by a preponderance of the evidence that his exposure to Roundup was a substantial factor in causing his non-Hodgkin's lymphoma? The 2nd phase of the trial, with the same jury, focuses on Bayer's liability and damages and begins on March 20th 2019.

On March 27 2019, the jury awarded Hardeman more than $5 million in compensation and an additional $75 million in punitive damages. On July 15th 2019, the judge reduces the punitive damages from $75 million to $20 million to comply with the Supreme Court's constitutional standards, but dismissed Bayer's request for a new trial for compensatory damages.

On December 13th 2019, Bayer lodges an appeal (Case: 19-16636) claiming that "serious errors" were made in the case and it should have never made it to trial. On Decemeber 20th 2019, the US government files an amicus brief in support of Monsanto saying that glyphosate is not a carcinogen and as a result a warning on the label was not required as California state law demands.

On May 14th, 2021, the US Court of Appeals for the Ninth Circuit affirmed the District Court of the Northern District of California’s judgment in favor of Edwin Hardeman in his action alleging that Monsanto’s pesticide, Roundup, caused his non-Hodgkin’s lymphoma.

On August 16, 2021, Monsanto/Bayer files a petition with the U.S. Supreme Court to reverse the appeals court verdict.
It presents 2 questions:
1- Whether FIFRA preempts a state-law failure to-warn claim where the warning cannot be added to a product without EPA approval and EPA has repeatedly concluded that the warning is not appropriate.
2- Whether the Ninth Circuit’s standard for admitting expert testimony is inconsistent with this Court’s precedent and Federal Rule of Evidence 702.

On June 21th, 2022, the U.S. Supreme Court refused to take up Monsanto's appeal of the jury's $25 million award (21-241).