But he acknowledged the program might not work for everyone, like those in very small villages not connected to roads, or those who have settled as squatters in national parks, where coca growing exploded in recent years.

“These families will have to relocate,” the vice president said.

Campo Elías Chagua, 50, a coca farmer outside a town called La Hormiga, hopes he will not have to move.

On a recent morning, Mr. Chagua trudged through a dense rain forest of vines and tropical birds, which suddenly opened up to his coca farm. He and his 27-year-old son spent the day harvesting the coca bushes as a fellow coca farmer, Arnulio Quiñones, looked on.

“The FARC would keep order,” said Mr. Chagua’s wife, Mariana Narváez, remembering the old days.

But, they wondered, would the government? There was still no electricity here, no running water. And now officials were asking them to give up their coca.

“We could go back to violence if the government doesn’t hold up its end of the deal on this,” Mr. Chagua said.

That day, they visited the lab of a neighbor, who was processing cocaine paste with help of a hired hand. The smell of gasoline and raw leaves hung in the air.

“He just wouldn’t survive off of black pepper,” Mr. Quiñones said.