A program to destroy the Colombian cocaine crop by spraying herbicide may end because of concerns the active ingredient in the herbicide could cause cancer. Experts say the result may be a surge in the country’s cocaine production, according to Time.

Under the herbicide program, which is backed by the United States, Colombian police crop dusters have sprayed herbicide containing glyphosate on more than 4 million acres of the nation’s coca fields in the past 20 years.

A recent report by the World Health Organization (WHO) finds that glyphosate may cause cancer, the article notes. Colombian President Juan Manuel Santos, citing the report, urged the Colombian National Narcotics Council to phase out aerial spraying. “The risk does exist,” he said. “We need a system that is more efficient and less damaging.”

The WHO report concludes glyphosate has been linked with tumors in rats and mice, and states there is some limited evidence that people who work with the herbicide may be at increased risk of developing non-Hodgkin lymphoma. The report, by WHO’s International Agency for Research on Cancer, concludes glyphosate “is probably carcinogenic to humans.”

William R. Brownfield, who heads the U.S. State Department’s Bureau of International Narcotics and Law Enforcement Affairs, says glyphosate is the world’s most commonly used herbicide. “There is not one single verified case… of cancer being caused by glyphosate,” he told the magazine.

The Colombian drug eradication program uses a higher concentration of glyphosate than is used for regular agricultural purposes. The herbicide used in Colombia is sprayed over populated areas, and can land on people, the article notes. A nationwide study of hospital visits found a higher incidence of rashes, respiratory problems and miscarriages in coca-growing areas sprayed with the herbicide between 2003 and 2007.