Thomson Reuters

Bayer's shares dropped 12% after a jury found a customer developed cancer from using its Roundup weed killer.

Another jury previously found that Bayer's Monsanto unit failed to warn customers of the potential cancer risks of its weed killers.

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Shares in Bayer plunged 12% in morning trading Wednesday after a San Francisco jury found one of its customers developed cancer after using its Roundup weed killer in his yard.

The decision strikes another blow to the German pharmaceuticals group. In August, a jury ordered its Monsanto unit to pay $289 million after determining it failed to warn customers of the potential cancer risks of two of its weed killers, Roundup and Ranger Pro. The verdict was cut to $78.5 million on appeal.

Bayer — which generated close to €40 billion in sales (about $45 billion) and €4 billion in operating profits in 2018 — took control of Roundup after it acquired the agrochemical company Monsanto last summer. The jury will now decide whether to hold Monsanto liable, raising the prospect of another multimillion-dollar verdict.

Bayer's stock has slumped by a third in the past year, wiping more than $20 billion off its market value. Headwinds remain, as the company faces lawsuits from more than 11,000 farmers, home gardeners, and landscapers. It's set to appear in six more trials in federal and state courts this year.

The plaintiff's attorneys said he developed non-Hodgkin lymphoma after 26 years of regularly using Roundup to tackle weeds and poison oak, according to The Wall Street Journal. The active ingredient in Roundup and Ranger Pro is glyphosate, an herbicide.

"We are disappointed with the jury's initial decision, but we continue to believe firmly that the science confirms that glyphosate-based herbicides do not cause cancer," Bayer said in a press release. "Bayer stands behind these products and will vigorously defend them."

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