BOGOTÁ, Colombia — Colombia just discarded a cornerstone of the American-backed fight against drugs, blocking the aerial spraying of coca, the plant used to make cocaine. Bolivia kicked out the United States Drug Enforcement Administration years ago and allows farmers to grow small amounts of the crop. Chile, long one of Latin America’s most socially conservative countries, is gathering its first medical marijuana harvest.

Across the Americas, governments are increasingly resisting the tenets of the United States-led approach to fighting drugs, often challenging traditional strategies like prohibition, the eradication of crops, and a militarized stance to battling growers in a fundamental shift in the region.

“For the first time in 40 years, there is significant pushback from Latin American countries, which endured much of the drug war’s suffering,” said Paul Gootenberg, a historian on Latin America.

In many ways, the resistance reflects the declining influence of the United States in Latin America and a sweeping sense that its methods to fight drugs in the region have failed.