The plaintiffs will next have to prove Roundup caused cancer in specific people whose cases will be selected for test trials, a phase Chhabria in his Tuesday opinion called a "daunting challenge".
Johnson sprayed Roundup and a similar product, Ranger Pro, at his job as a pest control manager at a San Francisco Bay Area school district, according to his attorneys. Wisner said Johnson read the label carefully and even contacted the company after developing a rash, but was never warned it could cause cancer.
Johnson's attorney said in opening statements that since 2000, there has been mounting evidence that glyphosate causes genetic damage. Monsanto has vehemently denied such a connection.
The trial was expedited due to Johnson's poor health, who will likely spend the last days of his life in a court room. "We have sympathy for anyone suffering from cancer, but the science clearly shows that glyphosate was not the cause".
Monsanto developed glyphosate in the 1970s, and the weed killer is now sold in more than 160 countries.
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A US judge in San Francisco says evidence seems weak that Roundup weed killer causes cancer, but experts can still make that claim at trial.
Beate Ritz, an epidemiologist at the University of California, Los Angeles, testified for the plaintiffs that her review of scientific literature led her to conclude that glyphosate and glyphosate-based compounds such as Roundup can cause non-Hodgkin's lymphoma. Homeowners use it on their lawns and gardens.
Lawsuits by more than 400 farmers, landscapers and consumers who claim Roundup caused them to develop non-Hodgkin's Lymphoma, a type of blood cell cancer, have been consolidated before Chhabria. But the World Health Organization in 2015 classified glyphosate as "probably carcinogenic to humans".
A flurry of lawsuits against Monsanto followed, and California added glyphosate to its list of chemicals known to cause cancer.