German chemicals giant Bayer, which last year bought Monsanto for $63 billion, faces a growing bill after the US group was hit with a new legal blow over its weed killer Roundup.

From the toxic legacy of weedkiller Roundup to fears about Monsanto's use of genetically modified seeds, here are some controversies that have put the two companies in the spotlight.

Heroin and Agent Orange

Founded in Germany in 1863, Bayer is still best known for making aspirin. But more infamously, it briefly sold heroin in the early 20th century, which it marketed as a cough cure and morphine substitute.

During World War II, Bayer was part of a consortium called IG Farben that made the Zyklon B pesticide used in Adolf Hitler's gas chambers.

Through a series of acquisitions over the years, Bayer has grown into a drugs and chemicals behemoth and now employs some 100,000 people worldwide.

Much of its success in recent years was built on blockbuster drugs like Eylea -- used to treat damage to the retina - or prostate cancer treatment Xofigo.

Monsanto was established in St Louis, Missouri in 1901, setting out to make saccharine.

By the 1940s, it was producing farm-oriented chemicals, including herbicide 2,4-D, which was combined with another chemical to make the notorious Vietnam War-era defoliant Agent Orange.

Goodbye 'Monsatan'

In 1976, Monsanto launched probably its best-known product, the weedkiller Roundup.

In the 1980s, its scientists were the first to genetically modify a plant cell. Monsanto then started buying other seed companies and began field trials of GM seeds.

It eventually developed soybean, corn, cotton and other crops engineered to be tolerant of Roundup.

Company bosses say that alongside applying big data to farmers' interventions on their crops, such resistant plant and pesticide combos will contribute to fatter harvests - needed to feed a world population expected to hit 10 billion by 2050.

Dubbed "Monsatan" and "Mutanto" by critics, the US firm has for decades been in the crosshairs of environmentalists - especially in Europe - who believe that GM food could be unsafe to eat.

Campaigners also abhor Monsanto's production of glyphosate-based Roundup, which some scientists have linked to cancer although other studies dispute this.

Hoping to ditch Monsanto's reputation, Bayer has said it plans to drop the name from its products.

Lawsuits pile up

In an agriculture industry preparing to nourish a global population surge, Bayer had been keen to secure Monsanto's market-leading line in GM crop seeds designed to resist strong pesticides like Roundup.

It was also lured by Monsanto's data analytics business Climate Corp, believing farmers will in future rely on digital monitoring of their crops.

But the takeover came at a high cost.

Beyond the eye-watering price tag, Bayer had to give up much of its seeds and agrichemical business to satisfy competition concerns.

Those divestitures have gone to Bayer's homegrown rival BASF.

But more worryingly for Bayer, Monsanto faces 13,400 lawsuits in the US and has already lost three major cases there over Roundup.

On Monday, a jury in Oakland, California, ordered the chemicals giant to pay more than $2 billion in damages to a couple that sued on grounds the product caused their cancer, lawyers said.

That followed a verdict in March when a San Francisco court ordered the firm to pay another cancer-stricken plaintiff $75 million in punitive damages, $5.6 million in compensation and $200,000 for medical expenses.

And that ruling in turn came after an August state court trial in which jurors awarded school groundskeeper Dewayne Johnson $289 million in damages over his terminal non-Hodgkin's lymphoma. That figure was later reduced to $78.5 million.

Analysts estimated last year that the legal cases could cost Bayer up to $10 billion.

Bayer is appealing the cases and stands by its position that "regulatory authorities around the world consider glyphosate-based herbicides as safe when used as directed".

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