Some scientists say it’s too soon to tell if a popular weedkiller found in products all over the supermarket is safe.

By now, many consumers have heard of glyphosate, the active ingredient in the herbicide known as Roundup, and warnings about its presence in many of their favorite foods. From oatmeal to granola bars, ice cream to even orange juice, trace amounts of the chemical can be found throughout your local supermarket.

It’s the world’s most widely used weedkiller—a blockbuster for Monsanto Co. since it was introduced in the 1970s. The vast majority of U.S. corn and soybeans have been genetically modified to withstand it, making it a critical component of modern farming. But in 2015, the International Agency for Research on Cancer—an arm of the World Health Organization—labeled it a probable carcinogen. Since then, it’s become a legal headache for Monsanto, and now Bayer AG, which bought the company in June for $66 billion.