Like thousands of other Bolivians, Marcela Lopez Vasquez's parents migrated to the Chapare region, in the Andean tropics, desperate to make a living after waves of economic and environmental upheaval hit farming and mining communities in the 1970s and '80s.

The new migrants, who spread across the undulating green hills here, planted bananas. They planted yucca and orange trees. But it was in the coca leaf that thrives in this climate that they found the salvation of a steady cash crop – and themselves at the nexus of the American "war on drugs."

The coca leaf has been sacred in Andean society for 4,000 years and is a mainstay of Bolivian culture. It is chewed by farmers and miners, enlisted in religious ceremonies, and used for medicinal purposes. "The only resource for maintaining our families is the coca leaf," says Ms. Lopez Vasquez. "With coca we maintain our families: We dress ourselves, take care of our health, and educate our kids."

Coca is also used to make cocaine. To American society, from White House officials to worried parents, the nation's drug problems start in places like the back fields of the Chapare, where neat rows of coca's spindly bushes, bursting with bright green leaves, stand head high. Bolivia is the world's third largest grower of coca, behind Colombia and Peru.

For decades the coca growers here, Lopez Vasquez among them, resisted US-backed forced eradication in a long simmering protest that defined US-Bolivian relations and often turned violent. Growers in the Chapare scored a victory in 2004 when they were granted the right to grow a small plot of coca per family. But a turning point came with the 2006 election of Bolivian President Evo Morales, a former coca grower from the Chapare and still the head of its unions, who promised an end to the old US-Bolivian paradigm. Within three years of his presidency, Mr. Morales kicked out the United States Drug Enforcement Administration (DEA), as well as the US ambassador, accusing both of fomenting opposition. Last year Bolivia became the first country ever to withdraw from the United Nations 1961 Single Convention on Narcotic Drugs for the charter's failure to recognize the traditional use of the coca leaf.

Now the Chapare is once again a nexus – but this time for a new government experiment markedly different from former US drug policy. Today, farmers unions partner with government agencies to control coca production, reducing the amount of the leaf cultivated across Bolivia, as well as the quantities destined for illegal uses. This cooperation is new, and the very acceptance of coca crops in the Chapare defies US wishes.

The US, in fact, has voiced deep skepticism about Bolivia's commitment to the international fight against narcotics, condemning La Paz in a 2012 report for "failing demonstrably" in its antinarcotic obligations.

For the residents of the Chapare, however, the "nationalization" of Bolivia's drug fight means the preservation of a lifestyle and a basic income without the threat of constant conflict.

"I am a coca producer, and they made us take out our crops so cocaine would disappear and narcotraffic would disappear," says Felipe Martinez, who heads a state entity in charge of monitoring and eradicating coca that exceeds legal limits in the Chapare. "But that didn't bring results. It brought blood, sorrow, orphans. We lost the right to be people."

Bolivia's more go-it-alone approach symbolizes a fundamental shift in the drug war in Latin America – one that is creating a tense new relationship between the US and its southern neighbors and could help determine how many drugs ultimately end up on urban streets.

Countries across the region are adopting a more autonomous, sometimes nationalistic, response to narcotics control that increasingly questions Washington's priorities and prescriptions. From Bolivia, where drugs are produced, to Mexico and Guatemala, where they transit through, to Brazil, where they are increasingly consumed, officials are forging new policies or floating ideas to deal with a problem they believe 40 years of US-dictated solutions hasn't curbed.

The relationship between Latin America and the US has always been at its most fraught over the war on drugs, ever since Richard Nixon launched the initiative in the 1970s. Nowhere has Washington's scolding finger been more in the face of its Latin American counterparts. Nowhere has Latin America felt it has fewer options than to just acquiesce, dependent as it is on US aid and military might to overcome the cartels that control narcotics trafficking.

But in the past five years, frustration has mounted. Gruesome drug crimes have brought record levels of violence to swaths of Mexico and Central America, despite the billions that the US has poured into the antinarcotics fight.

Leaders in the region are pleading for new alternatives – some are even discussing legalized drug markets – no matter how much those ideas might alienate the US.

The restiveness reflects a growing political assertiveness in the region. While Latin America has always been weary of the heavy hand of the US, Bolivia and Venezuela have taken their indignation to a new level, refusing to cooperate with the DEA and other US officials. Many countries also seem less inclined to genuflect toward Washington on other issues, from trade to foreign policy.

Yet it is the drug issue that will most define US relations with the hemisphere – and have the most impact around the world. Latin America remains the world's No. 1 supplier of cocaine, and how various countries deal with their coca tracts will not only affect the flow of narcotics, but might lead to new strategies in the drug fight.

For now, the range of ideas and possible routes of action vary widely. Leaders in the most vociferous countries even concede that their ideas might not work. But what seems certain is that the days of policy dictated so heavily from Washington are vanishing.

"There is a desperate call from Latin America for peace, which includes a new model for drug policies," says Milton Romani, Uruguay's ambassador to the Organization of American States (OAS).

Otto Perez Molina is hardly a squeamish liberal. The president of Guatemala, who took office in January, is a retired military general who once served in the country's brutish special forces (Kaibiles). The day after his inauguration, the silver-thatched leader fulfilled a campaign promise to bring an "iron fist" to lawlessness by militarizing the drug fight in Guatemala.

So it stunned the region when the Guatemalan president, in March, floated a provocative initiative to deal with the violence spiraling out of control in another way: He called for an entire rethink of the war on drugs, including the option of the state running a legally regulated drug market.

The idea of pursuing more liberalized drug policies rather than harsher punishments is hardly novel in Latin America. But such notions are usually championed by intellectuals and academics on the left. They have rarely been promoted by sitting presidents.

Yet 2009 marked a hinge moment: A Latin American commission on drug policy headed by three former presidents, from Mexico, Brazil, and Colombia, published a report declaring the war on drugs a failure – one that desperately needed to shift from repression to prevention. Two years later, the group pulled former officials and business leaders from around the world into the Global Commission on Drug Policy, which went further, rallying nations to consider ways to regulate drugs rather than just crack down on their use.

Amid this growing consensus, Mr. Perez Molina, and perhaps even more significant, President Juan Manuel Santos of Colombia, began floating similar ideas. At a talk in London in late 2011, Mr. Santos, a former defense minister, said the war on drugs was stuck on a "stationary bike."

Other leaders rallied to their side, including Laura Chinchilla, the president of Costa Rica. Mexico's conservative president, Felipe Calderón, while not siding with legalization, has said in moments of exasperation that if US consumption cannot be controlled, the hemisphere should consider "market solutions," meaning some kind of regulated legal exchange.

Drug policy became a centerpiece of the OAS Summit held in Cartagena in April, too. The organization set a mandate to study drug policy alternatives and deliver a review in a year's time – what many consider a significant step.

Since then, in the boldest proposal to date, President José Mujica of Uruguay announced the possibility of establishing a legal marijuana market, in which the drug would be produced and distributed under state control. It would be the first market of its kind in the world.

Yet many drug policy experts in the region question whether a state-run exchange could work. Santos in Colombia criticized Mr. Mujica's plan, saying "unilateral" action is not the way forward. Others say corruption – in Guatemala, for instance – would only empower drug traffickers if there were a legal market. Still others note that talk of legalization, which focuses on marijuana, misses the point since cocaine is the big concern and no one is suggesting legalizing it.

But the debate, which has evolved from one led by activists to former presidents to current heads of state in Latin America, suggests that some kind of fundamental change is inevitable. "

For former presidents, it is easy to say 'let's have a debate' on a topic that they cannot do anything about," says Daniel Mejia, who runs a drug policy research center at the University of los Andes in Bogotá. "But having sitting presidents [say that] is a completely new thing that we've seen during the past five years."

While legalization is the buzz word that always draws media attention – and virulent US protests – Latin America is leading the way today in considering a whole range of alternative policy options. It is beginning to focus on drug use as a public health issue, and not a crime, through judicial rulings and legislation, following in the footsteps of Western Europe in the past two decades. Several countries have already introduced decriminalization of possession of small amounts of drugs, mainly marijuana, and are proposing lighter sentences for minor trafficking offenses.

In Argentina, for instance, the Supreme Court ruled in 2009 that it is unconstitutional to punish someone for possessing drugs for personal consumption. Mexico decriminalized personal use that same year, although only for minute quantities. Colombia's Constitutional Court in June upheld an earlier law that decriminalized personal consumption of marijuana and cocaine, while lawmakers in Brazil are debating whether to make possessing small quantities a noncriminal offense as well.

The moves mark a swing back from harsher sentences and an escalation of the war on drugs that have been a hallmark of US influence in the region since the 1980s, according to Martin Jelsma, a drug policy expert at the Transnational Institute in the Netherlands.

Bolivia's changes have been dramatic in their own way. On a recent morning, the Chapare, a New Hampshire-size province in the middle of the country, lies under a heavy mist. Wooden houses propped up on stilts sit among plots of banana trees.

Women in bright velvet skirts and brimmed hats, characteristic of the area's Quechua Indians, shop at local markets. Chickens scour dirt yards and dogs wander the roads. It's a peaceful tableau.

Yet the quietude has only come here recently, residents say. Rosa Montaño, who migrated to the Chapare as a young woman, still farms her legally allotted coca field, called a cato, which helps her maintain her home, a small unpainted wooden room. She lives there with her daughter, Irma Cornejo, who grew up in the height of the coca grower conflict, and her grandchildren. Both say dramatic changes have occurred since Bolivian rural police units, backed by the US, stopped coming in and forcing the eradication of coca.

"They brought my brother here and beat him," Ms. Cornejo says. "Now that doesn't happen.... It's calmer now. The kids don't see those beatings that I've seen; and the abuse, it isn't here anymore."

Under the current system, the responsibility for inspecting the size of the coca crops lies with the coca-growing unions and a government-monitoring body. It includes satellite surveillance. The Bolivians are backed in the program, called "social control," with funding from the European Union.

Farmers who consistently grow more than the allotted amount of coca, or who produce it outside designated areas, are subject to forced eradication. Bolivia's anti-narcotics forces also still search out cocaine labs and confiscate illegal drug shipments.

"[Bolivia] challenged the United States, and it turned out the United States was not the omnipotent force in drug war policy that it seemed to be," says Kathryn Ledebur, director of the Andean Information Network, a Bolivia-based advocacy group. "And it was important to establish that for everyone in Latin America."

The US isn't completely divorced from the process. It continues to fund the antinarcotics effort in Bolivia through the US embassy, but the aid has dropped from about $40 million in 2006 to $10 million in 2012, according to US State Department figures.

Instead, Bolivia has increasingly been partnering with both the EU and Brazil, with whom it shares a long, porous border. Brazil, which is now the second-largest consumer of cocaine in the world, plans to use drones and other technology to help patrol the Amazonian area that the two countries share.

Brazil's ambassador to Bolivia, Marcel Biato, says the countries have been cooperating more closely since 2010, at the request of La Paz. "I think this link has to do with various internal elements, but also a clear distancing from the US and perhaps greater confidence that Brazil can develop an alternative to all of the historic problems," he says.

As part of the social control program, the coca unions educate local growers about the importance of keeping cultivation at legally accepted limits, which markedly increased during the early years of the Morales administration. When the US government was heavily involved in the eradication effort, before 2004, Bolivia was allowed to plant 46 square miles of coca a year for traditional uses. Since then, the Bolivian government has boosted that amount to 77 square miles.

To further aid growers, Morales is trying to find more legal international markets for the leaf, something the UN charter on narcotics prohibits. In Bolivia, coca is widely used in teas and chewed (bags of leaves are sold on street corners) as well as incorporated into consumer items such as candy, cookies, granola bars, and toothpaste.

The leaf acts as a mild stimulant – it produces no major high like purified cocaine – but can help overcome fatigue, hunger, and thirst. For these reasons, it has long been used as a medicine – something Bolivians have turned to for everything from nosebleeds to indigestion to dealing with childbirth.

The question is how much of it gets made into cocaine. Growers like Lopez Vasquez say there are always people who want to produce more coca than the state allows, or who turn it into cocaine and ship it off to Brazil and as far away as Africa and Europe. But as she stands in a coca field in her hometown, Lopez Vasquez is confident that coca cultivation will decline in the Chapare because the powerful unions are committed to working with, instead of fighting, the government to manage cultivation.

Mr. Martinez, the state official and coca grower, agrees. "More than ever we have applied ourselves to agree on mechanisms between the state and the coca producers so we have positive results," he says in his Chapare office, where he pulls out some coca leaves from his drawer and slips them in his cheek. "We haven't had any deaths. We haven't had any injuries. There has been no blood spilled and no conflicts."

Yet not everyone is convinced the situation is under control. Even though coca leaf cultivation has stabilized in recent years, the US believes that Bolivia is producing far more than even the limits La Paz has set – and thus the potential for cocaine production remains dangerously high.

According to the US's annual International Narcotics Control Strategy Report, the country cultivated 133 square miles of coca in 2010, down slightly from 2009's 135 square mile estimate. From this, the US estimates that the pure cocaine potential remains at 195 metric tons, or 70 percent higher than in 2006.

Further, the US believes Bolivia's ability to arrest major traffickers has eroded since the DEA was kicked out in 2008. "Expelling DEA has seriously harmed Bo-livia's counternarcotics capability, especially in regard to interdiction," the report says.

Bolivia has certainly seen setbacks. In 2011, an ex-commander of the nation's antidrug police and current head of a drug intelligence agency was arrested by the DEA in Panama and subsequently pleaded guilty to trafficking. While no reliable evidence has surfaced linking other top Bolivians to the drug trade, accusations swirl that the links go beyond the one official.

"The highest levels of governance in those countries [Bolivia and Venezuela] are complicit in the global drug trade now," says Michael Braun, the former chief of operations for the DEA.

Bolivia represents one of the most extreme examples of countries diverging with the US over drug policy. But others are starting to question elements of America's priorities as well – some of them surprising.

When Mexican President Calderón was elected in 2006 and made fighting the scourge of drug cartels the cornerstone of his presidency, he was feted in American circles. A new era of "co-responsibility" was ushered in as the US signed off on a $1.6 billion aid package to help Mexico fight trafficking.

But as the years wore on and the toll mounted – including more than 50,000 dead in six years, even as top traffickers were caught and extradited to the US – so did public criticism of the strategy. It ultimately cost Calderón's conservative National Action Party the presidency in July elections. The incoming president, Enrique Peña Nieto, who takes office in December, has promised to "reduce violence" instead of focusing single-mindedly on netting traffickers and stanching the flow of drugs.

What that means exactly isn't clear. But ideas are being floated that would make American officials grimace, according to Alejandro Hope, a security analyst and former official in Mexico's intelligence agency.

He argues that Mexico should go after the most violent criminals, not the ones that move the most drugs. He says the country should quietly end eradication efforts, calling it a "pointless exercise." "What Mexico can't do and should not attempt to do is stop the flow of drugs into the US," says Mr. Hope.

US priorities are also under assault in Central America, where violence and trafficking have migrated after crackdowns in Mexico. In Honduras, DEA squadrons have been involved in three fatal shootouts in less than three months. The teams, called Foreign-deployed Advisory and Support Teams (FAST), have been accompanying local forces throughout Honduras and other countries in Central America.

But the program, which was begun quietly in Afghanistan and expanded into Central America, exploded onto the front pages in May after a group of Hondurans, who claim to be innocent victims, were shot at by Honduran forces, accompanied by the DEA, as they plied the waters of the Mosquito Coast in canoes. Four were killed. Since then, the DEA has been involved in two more fatal incidents.

The US and Honduras have defended the raids, and so does Mr. Braun, an architect of the program. "The government of Honduras is asking for more DEA resources, rather than backing away from the incidents. That is pretty telling," says Braun.

A US official echoes those sentiments. He says the success so far of Operation Anvil, under which the FAST teams were dispatched in April, is clear: Honduran forces, with DEA support, have interdicted 2,300 kilograms of cocaine from smuggling flights, mostly coming from Venezuela. "It showed us there is unchallenged illicit air traffic going through Honduras, and Honduras has not been able to control it until now," he says.

More broadly, he notes that the US has put more resources into the "soft" side of the drug fight, not just eradication and hardware but in institution-building and anti-corruption measures. "The old paradigm, the idea of a war on drugs, is long past," he says. "We realize there are a lot of other pieces of it that go well beyond eradicating a coca field."

Still, the incidents in Honduras and the perception of a continued militarization of the fight has provoked an outcry from human rights workers and others in Honduras and beyond. "The use of the military has just caused violence to spiral to levels we have never seen," says Sandino Asturias, head of the Center for Guatemalan Studies.

How far all this change in Latin America, whether in Lopez Vasquez's backyard or in the presidential palace in Bogotá, will go remains uncertain. But the days of Washington dictation seem to be diminishing. As John Walsh at the Washington Office on Latin America puts it: "No one is taking marching orders from the US anymore."