A police plane sprays herbicides over coca fields in El Tarra, in the Catatumbo river area of Colombia on June 4, 2008.
Luis Robayo—AP
By Naina Bajekal
May 15, 2015

Colombia’s government ordered a halt Thursday to the use of a herbicide that has formed a major part of U.S.-backed efforts to wipe out cocaine crops in the country, the Times reports.

The country’s Health Ministry had cited concerns after the World Health Organization reclassified the weed-killer glyphosate as a carcinogen (a cancer-causing substance) in March. The U.S. Environmental Protection Agency’s 2012 report disagreed, saying there was a lack of convincing evidence that the herbicide causes cancer in humans.

Over the past two decades over 4 million acres of land in Colombia have been sprayed with the herbicide, which kills coca plants (whose leaves are used to make cocaine).

The change in strategy may put a strain on Colombia’s relationship with the U.S. for the first time, as the two countries are usually close allies when it comes to a hard-line approach in the war on drugs. But earlier this month, a White House survey found that the amount of land in Colombia used to grow coca increased by 39% last year

Peru and Bolivia are the two other main cocaine-producing countries, but both avoid chemical herbicides, opting for a more labor-intensive manual eradication instead. This is riskier in Colombia, where the rebel guerrilla fighters have long protected coca crops.

Read More: Experts Fear Surge in Cocaine Supply to U.S. as Colombia Mulls Ending Coca Eradication

Write to Naina Bajekal at naina.bajekal@time.com.

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