First Brazilians started gobbling up junk food. Now they’re clamoring for weight-loss drugs.

Brazil, where the obesity rate has surged over the past decade, is now the biggest growth driver for weight-loss treatments in the world and the No. 2 market for Saxenda, Novo Nordisk’s industry-leading drug. Waistlines have expanded after the country became a key target for makers of packaged food.

Whether they can afford it or not, increasing numbers of frustrated patients are paying more than $150 a month out of their own pockets for the medicines.

“We have a huge amount of people coming here wanting Saxenda,” said Bruna Kury, a doctor in Rio de Janeiro. Some have even started using the treatment before they visit her office, buying the medication over the counter, she said.

A global obesity epidemic is opening up avenues of growth for the drug industry in developing nations like Brazil and other markets beyond the U.S., where almost four in 10 adults fall into that category. More than 700 million people are now considered obese worldwide, raising the risk of diabetes, heart disease and cancer, and driving health care costs higher.

After launches in Mexico and Chile, Novo plans to bring the injectable drug to two more Latin American nations, adding to its list of more than three dozen markets globally. In Brazil, like everywhere aside from limited programs in Denmark and the United Arab Emirates, the costs of obesity medications aren’t covered by the state-run health system.

“We’re surprised by the uptake and the willingness to pay out of pocket,” Novo Chief Executive Officer Lars Fruergaard Jorgensen said in an interview. “We see stronger growth outside the U.S. than in the U.S.”

Tatiana Chaves, who lives in the affluent Rio neighborhood of Ipanema, said she cut her weight from a life-threatening peak of more than 400 pounds to 230 pounds through bariatric surgery, exercise, diet and, finally, medication, which she was able to buy with help from her father. She lost the last 30 pounds with Saxenda, but was forced to stop because of the cost.

The appetite for weight-loss treatments in this South American nation of more than 200 million reflects a mounting health problem that in many cases requires medicine, on top of changes to diet and exercise, according to doctors. Brazil’s obesity rate has surged to more than 22 percent, a trend they attribute to unhealthy food, a lack of physical activity and people staying indoors to avoid violence in some areas. Genes also play a role.

Food companies have grown increasingly aggressive in ensuring low-cost products are widely available, contributing to weight gain in nations such as Brazil. They also pressure governments to hold off on passing soda taxes or laws that could hurt sales, according to Marion Nestle, a nutrition, food and public health specialist at New York University.

“Developing countries with rising incomes are great places to market relatively inexpensive but highly profitable junk foods,” she said in an e-mail.