A decade ago, Myanmar seemed on course to wipe out the opium fields and heroin jungle labs along its eastern border, the notorious Golden Triangle. Today, valley after valley in these mist-shrouded mountains is covered with resplendent opium poppies, tended by farmers who perch on steep hillsides to harvest the plant’s sticky, intoxicating sap.

Poppy cultivation in Myanmar has nearly tripled since 2006, reaching close to 150,000 acres, according to surveys carried out by the United Nations. Yet even that steep rise fails to capture the full extent of Myanmar’s resurgence as a major player in the global heroin business. Over the last few years, an increasing number of farmers here have produced two opium crops a year, experts say; the second crop is not included in the United Nations surveys.

Growing opium poppies is illegal in Myanmar, but farmers in this remote and desperately poor region say they have few viable options.

“We don’t want to grow poppy our whole lives,” said Sang Phae, 36, a farmer who spent nearly a decade in Thailand and returned with knowledge of modern cultivation techniques. “We know this is not good for society, and other countries don’t like it. But there’s no other way for us now.”

• Slide Show: Poppies Bloom Again in Myanmar

Myanmar remains a distant second to Afghanistan in global production of opium, the key ingredient in heroin. The United Nations estimates 550,000 acres in Afghanistan were dedicated to growing poppy last year, more than three times the area farmed in Myanmar. But Golden Triangle heroin has a reputation for superior quality and fetches much higher prices, especially in China, which appears to be the primary market.

Until the 1980s, Myanmar was the world’s largest supplier of heroin. Afghan production surged around the turn of the century, and supplies from the Golden Triangle plummeted when China pressured Myanmar ethnic groups along its border to stop growing poppy.

But instead of disappearing, opium production migrated south, away from the Chinese border, into areas of Myanmar controlled by a patchwork of ethnic groups, some of them allied with the government, some of them hostile. Although the government controls the big towns, upland areas are the fiefs of militias and ethnic armies, and the new center of the opium-growing business.

Myanmar’s return to drug trafficking, which also includes a thriving trade in methamphetamine, comes as the country opens up to the world and sheds the shackles of five decades of isolation and dictatorship. With the government preoccupied with the challenges of a budding democracy, opium money is lining the pockets of officials charged with cracking down on the illegal trade.

“The government turns a blind eye,” said John M. Whalen, the director of the United States Drug Enforcement Administration office in Myanmar until he retired in June. Even local government officials and military officers not directly involved in the trade are “paid to look the other way,” he said.

The Myanmar military, which is battling a number of ethnic armies even as the government professes peace, is wary of cracking down on drugs, fearing it could jeopardize tenuous alliances it has built with other militias, he said.

“You have various militia groups that are allowed to carry on because the government needs them,” said Mr. Whalen, who is now a director at Search, a Singapore-based consultancy.

Here in Bang Laem, poppies are grown in the mountainous backcountry controlled by longtime adversaries of the central government, the southern faction of the Shan State Army, a group that like many other upland ethnic groups has been fighting for autonomy from the central government.

Known as a “black zone,” the area is beyond government control and generally off-limits to foreigners. When a team of United Nations officials and journalists entered recently, the anti-narcotic police officers escorting them stayed behind. In early December, a week before the visit, a policeman was shot in a clash with rebels, United Nations officials said.

United States officials have long maintained that the Shan State Army South is involved in the drug trade, but a spokesman for the group, Sai Hla, said it was a “priority to eliminate the drug trade as much as we can.”

Those who accuse the group of being involved in the drug trade are “aiming to discredit the S.S.A. and our struggle,” he said.

Opium poppies have been used medicinally in this part of Myanmar for as long as anyone can remember. Small amounts of raw opium are used to treat fevers and stomach ailments, as a salve for snake bites and to treat ailing farm animals. But it was less than a decade ago that farmers took on opium as their main cash crop, abandoning cheroot tobacco, which is used for cigars.

Opium is not only more profitable, but the traffickers also help finance the cultivation. The opium boom drew farmers from other parts of Myanmar, and each year migrants have cleared swaths of hillside jungle to plant more poppies.

For farmers inured to conflict — almost everyone has a tale of being forced to flee the area when rival armies and militias battled — poppy has been a low-risk cash crop. It takes only four months from planting to harvest, and the bounty is portable: A year’s harvest for a typical farmer would fit inside a pillowcase.

“For many people in this country opium is not a problem, it’s the solution — a way for small-scale farmers to increase incomes to buy salt, rice, medicines and other essentials,” said Tom Kramer, a researcher with the Transnational Institute, an organization based in the Netherlands that tracks illicit drugs.

Villagers here say they find themselves locked into a treacherous opium economy. Brokers come to buy the raw opium as soon as it is harvested, but villagers must also reckon with the thuggish elements of the underground economy, including countless requests for payoffs, often at gunpoint.

“You can get double or triple from poppy, but you have to pay taxes to so many people,” said Ba Sang Jyan, 73, a grandmother who owns a small grocery store and has an opium field in her backyard.

Ms. Jyan and other villagers offer a long list of people they pay off: the police, the national army, the Shan State Army and military intelligence officers.

There is no electricity in the village, no government office or police station nearby, and before this year, when the United Nations carved out a dirt road that winds up a mountainside, the only access to the village was a rutted dirt footpath.

The United Nations has persuaded families here to dedicate part of their fields to coffee plants, a pilot project led by Jochen Wiese, an official with the United Nations anti-narcotics office who spent nearly three decades in Peru and started a successful crop substitution program there for farmers of coca, the raw ingredient of cocaine.

Crop substitution programs have failed numerous times before in Myanmar, notably with buckwheat and sugar cane, both of which were difficult to carry over dilapidated roads. Mr. Wiese says he is confident that he can make a name for Myanmar coffee and leverage his connections to make sure the coffee makes it to market.

Farmers say they are willing to try cultivating coffee, which takes three years to produce beans, but are not yet ready to abandon their poppy fields.

“We’d love to stop producing opium as soon as possible,” said Nang Wan, 23, who watched over her toddler as her husband harvested opium sap. “But if you only plant coffee, you’ll have nothing to eat.”

In December, Mr. Wiese spent three days answering a barrage of skeptical questions from opium farmers about coffee prices and whether he had the funds and the commitment of international donors who are helping finance the coffee program.

“We won’t overcome the drug problem here,” Mr. Wiese said in an interview. “But you have to show people that there is a possibility to change from an illegal economy. What we are doing here is just a first step.”

Wai Moe contributed reporting from Yangon, Myanmar.

A version of this article appears in print on January 4, 2015, on page A6 of the New York edition with the headline: Myanmar Returns to What Sells: Heroin

More information:

• Bouncing Back: Relapse in the Golden Triangle, Transnational Institute (TNI), May 2014

• Withdrawal Symptoms in the Golden Triangle: A Drugs Market in Disarray, Transnational Institute (TNI), January 2009