A man chews coca leaves in La Paz, Jan. 14, 2013, as indigenous people from the Quecha and Aymara celebrate Bolivia's re-admittance to the U.N. anti-narcotics convention. (GASTON BRITO/REUTERS)

Ever since the Spanish conquest, the Aymara and Quechua Indians of modern Bolivia have been a shadow majority. Banished to the margins of society, they have found relief from toiling in fields for a pittance by chewing an oval-shaped green leaf: coca, cocaine’s raw material, which is a mild stimulant in its unprocessed form.

“Coca is our culture, our food, our medicine. Coca is our life,” said Honorata Diaz, a farmer from El Chapare, one of two Bolivian regions where monitored coca leaf cultivation is legal, albeit under restricted conditions.

For years, producers of the ancient crop, such as Diaz, had fought stubbornly against forcible eradication in endless confrontations with army troops and U.S.-trained anti-drug officials. Now, finally, they have a reason to celebrate. Last week, Bolivia was readmitted to the U.N. anti-narcotics convention with a special dispensation that local coca use is legal.

“This is a historic triumph for Bolivia and the indigenous peoples,” Dionisio Nuñez, Bolivia’s deputy coca minister, said. On Tuesday, more than 100,000 Bolivian coca growers went out on the streets of the cities of La Paz and Cochabamba to cheer the decision.

The “sacred leaf” of the Andean Indians was declared illegal under the 1961 U.N. convention on narcotics, which stated that coca chewing should be eliminated, along with cocaine, heroin, opium and morphine use.

But Bolivia’s first indigenous president, Evo Morales, who is also the leader of the country’s largest coca growers union, withdrew from the U.N. convention last year, saying the country would not rejoin unless coca chewing was decriminalized.

After years of “coca diplomacy,” he finally persuaded member states to reverse the “historic wrong.” Fifteen countries objected, among them the United States, Russia and Mexico — well short of the 62 it would have taken to block Bolivia’s reentry. Officials in Washington said coca leaf legalization would “lead to a greater supply of cocaine and increased cocaine trafficking and related crime.”

Morales, a fierce critic of Washington who expelled U.S. drug agents in 2009 for allegedly plotting against his government, has said repeatedly that he can achieve a Bolivia of “zero cocaine but not zero coca” under his current policy, which allows small-scale coca leaf cultivation for local use, with growers carefully monitored.

Indeed, and to the surprise of many, Morales’s approach last year led to a 12 percent drop in total coca acreage in Bolivia, the first since he came to power in 2006, as well as a reported increase in seizures of processed cocaine.

Bolivia is the world’s third-largest supplier of cocaine, with much of the cocaine flowing through Brazil, which is suffering a crack epidemic, onto Europe. Brazil did not object to Bolivia’s reentry to the U.N. convention.

Despite Bolivia’s promising results, however, there are growing worries that international traffickers are introducing higher-yielding coca plants that compensate for smaller acreages and are also buying legally produced Bolivian coca leaf to make illegal cocaine.

According to one senior Bolivian anti-narcotics official, drug gangs based in Colombia and Mexico have colonized parts of the country where coca was once cultivated in the manner of a family business.

“There cannot be zero coca, but nor can there be unregulated cultivation of coca. You know, brothers, that a portion is diverted into drug-trafficking,” even Morales recognized last year. Increasingly, he has been urging coca leaf growers — roughly 300,000 families — to work together for more tightly controlled cultivation.

Drug policy may be changing worldwide — even in the United States, where Washington state and Colorado last year voted to legalize marijuana, although it remains illegal under federal law. In Bolivia, which has a meager $35 million annual budget this year to fight drug trafficking, Morales’s approach also differs markedly from the more coercive approaches of his Andean neighbors.

Ollanta Humala, while campaigning for the presidency of Peru, vowed not to carry out forced eradication, but he radically changed his stance upon taking office. After the country was named the world’s biggest producer last year, the Peruvian government increased its coca eradication target for this year to a record 54,000 acres — up nearly 60 percent from 2012.

Colombia has meanwhile fought a long war on drugs, with U.S. backing. But President Juan Manuel Santos has called openly for a debate about global policy change. The time has come, he has said, “to revise and look for alternatives to the war on drugs started 40 years ago because its results, unfortunately, are far from satisfactory.”

Bolivian officials say their country’s local markets for coca have helped stop the leaf landing in criminal hands. Indeed, while illegal coca leaf prices grew last year by an estimated 16 percent, they rose 31 percent in the legal market to fetch a total $353 million — 1.5 per cent of Bolivia’s gross domestic product.

“Social control among coca growers has been key,” the senior anti-drugs official said. “The nationalization of the fight against drugs is yielding results.”