KABUL—Opium production surged 61% this year in Afghanistan, as rising demand and worsening security helped the reversal of three years of progress in antidrug efforts, the United Nations reported.

One year after a blight ravaged the country's opium crops and raised hopes that farmers would turn their backs on opium cultivation, the farm-gate value of this year's harvest more than doubled to $1.4 billion, the U.N. said. The street value, which includes profits made by Taliban intermediaries, heroin refiners and drug cartels,...