Here’s what experts say about the risks and promises of traveling abroad for cost-efficient care.Last week, four Americans were kidnapped in the Mexican state of Tamaulipas, after crossing the border from Texas. Two were later found dead. A sister of one of the victims said they had gone to Mexico so one of them could get an abdominoplasty, better known as a tummy tuck.Every year, millions of Americans visit Mexico and other countries to obtain health care, a practice often called medical tourism. The National Exterior Commerce Bank in Mexico estimated that the industry was worth $5 billion before it declined during the coronavirus pandemic. For patients, the motivation is often financial.“Some of it is a desperate search for access” to medical care, said Felicia Marie Knaul, director of the Institute for Advanced Study of the Americas at the University of Miami.Many people cross the border for pharmaceuticals at greatly decreased prices from what you pay in the U.S. Others, especially Americans and Canadians in the past two decades, are traveling for surgeries or treatments. The Centers for Disease Control and Prevention says dental care, surgeries, fertility treatments, organ and tissue transplants and cancer treatment are the most common procedures for which people go abroad. Elective procedures are a major component of medical tourism, said Daniel Béland, a professor of political science at McGill University who has studied health policy.In 2016, the C.D.C. surveyed more than 93,000 people; of those who had left the United States for care during the previous year, Mexico was the most common destination.But while crossing national borders might be an affordable way to get high-quality care, medical tourism is largely unregulated, and it’s nearly impossible to track outcomes or the scope of procedures Americans obtain in Mexico.“There are really very few rules,” said David G. Vequist IV, director of the Center for Medical Tourism Research and a professor at the University of the Incarnate Word in San Antonio, Texas. Those that exist are vague, he added, and people are largely “making it up as they go along.”How many people go to Mexico for treatment?It’s hard to find solid data on medical tourism, said Valorie Crooks, a professor of geography at Simon Fraser University in Canada who has studied it for over a decade.She calls the industry a “triple U”: It’s “untracked, untraced and unregulated.”Most of the Mexican hospitals Americans visit are private and do not report their data to the federal government.Josef Woodman, the chief executive of Patients Beyond Borders, which serves as an international health care travel consulting agency and patient guide for people seeking care abroad, estimates that about 1.2 million Americans per year travel to Mexico for medical procedures. After a drop in medical tourism during the pandemic, Mr. Woodman said, he’s seen a spike in people seeking out treatment in Mexico as they got vaccinated.“After the first vax, people just flooded in,” he said.Complex dental treatments like root canals, veneers and full mouth reconstructions are among the most popular procedures, Mr. Woodman said. Los Algodones, near the California-Arizona border, is known as “Molar City” because it caters to this market.Billboards advertising pharmaceutical and medical services in Mexicali, Mexico.Guillermo Arias for The New York TimesThe most common destinations tend to be in Mexican states along the border, like Tamaulipas and Nuevo León, or those with popular beach towns, like Baja California Sur and Quintana Roo, according to Denise Rodriguez, who is studying for a Ph.D. in health geography at the University of Brasília in Brazil and interviewed hundreds of people involved in medical tourism in Los Algodones for her master’s thesis.By counting the numbers of private hospitals and medical professionals available, she found that Baja California Sur was the state with the most medical tourism.Why is the industry booming?Because the overhead costs of running a clinic or health care center in Mexico are much lower, patients typically pay far less than they would for a procedure in the United States, Dr. Crooks said.One study, which surveyed over 400 people near the U.S.–Mexico border about traveling to obtain health care, found that 92 percent cited lower costs in Mexico as guiding their decision. Andrea Miller, a clinical pharmacist in Arizona who led the study, was struck by just how widespread advertising, and infrastructure, for medical services was in a Mexican border town.“You look down the street and it’s like, pharmacy, pharmacy, optical clinic, dental clinic, pharmacy, dental clinic,” she said.Some patients also go abroad to circumvent red tape and restrictions that might stymie them at home, Dr. Crooks said.“You could be too young or too old for an orthopedic surgery; you could be too small or too big for a bariatric surgery — and then you find a surgeon in another country who’s willing to offer you the treatment,” she said.Other patients travel to get procedures that are illegal where they live, including abortions.Money explains only so much, said Ms. Rodriguez, who found that many travelers were simply looking for more personalized care and time with a doctor.“Why do people come back?” she said. “You are treated like a human being.”Medical tourism carries risks.While traveling for health care to certain areas of the world can be dangerous, experts said that for most patients, the risks have more to do with the medical procedure than the journey to obtain it.Patients embarking on medical tourism seek out care on their own and pay out of pocket, Dr. Crooks added. That may mean their primary-care doctors aren’t informed, potentially leading to problems when patients seek follow-up care at home.Foreign patients leaving a hospital in Tijuana. Mexico is a popular destination for Americans seeking cheaper medical care.Guillermo Arias/Agence France-Presse — Getty ImagesThe C.D.C. recommends that patients schedule a consultation with their U.S. health care provider before leaving the country for medical care, said Allison Tayler Walker, lead of the epidemiology and surveillance team in the Travelers’ Health Branch at the agency. The C.D.C. also advises patients to arrange follow-up care ahead of time with the professional who conducts the procedure abroad, as well as with a primary physician in the United States.There are also specific risks that come with certain interventions — for example, doctors caution against flying too soon after some surgeries, Dr. Béland said, because the procedures can make a person more susceptible to blood clots.Mr. Woodman recommended seeking out hospitals accredited by Joint Commission International. It’s important for patients to ensure that anyone giving them medical care has received proper training, said Dr. Patricia Turner, executive director of the American College of Surgeons. That includes not just the doctor performing surgery, for example, but also the person administering anesthesia or interpreting X-rays.Getting any service as complicated as a surgery in another country, with different laws and cultural norms, can be complicated. For instance, someone who receives improper medical care abroad may have little or no legal recourse and may not know what their rights are. And any procedure carries the risk of complications, and in another country, a patient may need to stay longer than expected for follow-up care or to recover, Dr. Crooks cautioned.“It’s not necessarily that those risks are higher when you go abroad,” Dr. Crooks said. “But your ability to remedy or address those risks could become more challenging.”