Shut out from mainstream medicine, some immigrants are buying expensive, unproven Covid therapies from “wellness” clinics or turning to the black market.FRESNO, Calif. — On a Tuesday afternoon in April, among tables of vegetables, clothes and telephone chargers at Fresno’s biggest outdoor flea market were prescription drugs being sold as treatments for Covid.Vendors sold $25 injections of the steroid dexamethasone, several kinds of antibiotics and the anti-parasitic drug ivermectin. Chloroquine and hydroxychloroquine — the malaria drugs pushed by President Donald J. Trump last year — make regular appearances at the market as well, as do sham herbal supplements.Health and consumer protection agencies have repeatedly warned that several of these treatments, as well as vitamin infusions and expensive injections of “peptide therapies” sold at alternative wellness clinics for more than $1,000, are not supported by reliable scientific evidence.But such unproven remedies, often promoted by doctors and companies on social media, have appealed to many people in low-income immigrant communities in places across the country where Covid-19 rates have been high but access to health care is low. Some turn to unregulated drugs because mainstream medicine is too expensive or is inaccessible because of language or cultural barriers.“It’s disappointing but not surprising” that people living below the poverty line have spent large sums of money for unproven treatments for Covid-19, said Rais Vohra, the interim head of Fresno County’s health department. “People are desperate and bombarded with misinformation and may not have the skills, time or context to interpret medical evidence.”The trend is not new. In 2014, Dr. Vohra published a case report on a Hmong woman who showed up at an emergency room in Fresno with life-threatening poisoning after overdosing on chloroquine that she had bought at the flea market under the label “red Tylenol.” He and his colleagues subsequently went to the market and to three smaller shops and found 35 different medications that were prescription-only or had been deemed unsafe by the Food and Drug Administration. “It was a real eye opener,” he said.Oralia Maceda Méndez, an advocate at a Fresno-based community group for Indigenous people from Oaxaca, Mexico, said those in her community feared that “the government might be trying to get rid of us.”Brian L. Frank for The New York TimesDuring the pandemic, many immigrants shut out of mainstream health care have turned to such markets for Covid-19 treatments. About 20 percent of Hispanic people in the United States lack health insurance, and the proportion is far higher among undocumented immigrants.What’s more, some immigrants mistrust doctors who don’t speak their language or who treat them curtly — and those concerns have been amplified by harsh political rhetoric directed at Mexicans and Central Americans.“My community fears that the government might be trying to get rid of us,” said Oralia Maceda Méndez, an advocate at a Fresno-based community group for Indigenous people from Oaxaca, Mexico. She has heard many stories from immigrants in her community who treat themselves for Covid-19 with penicillin, other antibiotics or a mix of vitamins and herbal therapies bought from shops or travelers selling medications bought in Mexico.“I am not surprised that people are taken advantage of,” she said. “We don’t have the care we need.”Some farmworkers have received unproven treatments at specialty clinics. A woman in Fresno recently described how her husband, a farmworker, had fallen so sick from Covid-19 that he couldn’t breathe or walk, but he refused to go to the hospital because he had heard rumors that undocumented immigrants had checked in and never left. She took him to a wellness clinic, where a doctor gave him injectable peptide treatments, recalled the woman, who requested anonymity because of her immigration status.She wasn’t prepared, she said, for the $1,400 bill, which included the cost of syringes and vials labeled thymosin-alpha 1, BPC-157 and LL-37. Pulling them out of a cabinet in the kitchen of her mobile home, she said she didn’t know exactly what they were, and she still feels the sting of the price.“I was shocked, but I was trying to act like it was OK because I had to be strong for my husband and my kids,” she said. He grew sicker despite the injections, but the family had no funds left for care. More than a month passed before he was well enough to return to the fields.Sandra Celedon, the president of a coalition of grass-roots organizations called Fresno Building Health Communities, said she and her colleagues have heard from several farmworkers and other low-income Latino immigrants who spent their savings on vitamin infusions and peptide therapies for Covid. “These folks are the poorest of the poor, and yet the doctors were requesting cash for their unproven treatments,” she said.Sandra Celedon, a leader of a coalition of grassroots organizations in Fresno, knows of several low-income immigrants who spent their savings on vitamin infusions and peptide therapies for Covid.Brian L. Frank for The New York TimesSome unregulated drugs can be dangerous. And even if they aren’t a health risk by themselves, they can lead people to postpone seeking help from doctors, which can be deadly. Delayed treatment is one reason Black and Hispanic people have died from Covid at twice the rate as white people in the United States.Alternative therapies can also limit a patient’s treatment options because doctors worry about toxic drug interactions, said Dr. Kathleen Page, an infectious-disease specialist at Johns Hopkins University School of Medicine in Baltimore.Undocumented immigrants from Mexico and Central America who have gone to the emergency room at her hospital often mention home remedies, vitamins or antibiotics they have injected or ingested before seeking care. “I’m not upset at patients when they tell me what they’ve taken,” Dr. Page said. “I’m upset about the system that makes it easier for them to get help from nontraditional places than from regular health care.”Unable or unwilling to talk with mainstream medical providers, some people turn instead to Facebook, YouTube or WhatsApp for advice. On Covid-19 Recipes and Home Remedies, for example, a Facebook page in Spanish that has about 10,000 members, people from the United States, Mexico and South America exchange tips on herbal concoctions, zinc, vitamin B12, ivermectin and chlorine dioxide — which has been tied to reports of respiratory and liver failure.Dr. Ignacio Guzman, who specializes in “anti-aging, regenerative and integrative medicine” at a clinic in an affluent area of northern Fresno, uses social media to advertise peptide therapy for a broad range of ailments. On Instagram, he promoted it in a photograph of himself getting a Covid-19 vaccine, writing that “integrating peptides with immunizations can double their efficacy!” (No clinical trials of Covid-19 vaccines support that claim, and the shots are highly effective on their own.)Another Instagram post, from March 2020, includes a photograph showing an intravenous line in the doctor’s arm above a caption in which he indicates that he is being infused with vitamin C. “This IV along with peptide therapy will limit my chances of acquiring infections such as Influenza A and the Corona Virus!” he wrote.The Fresno flea marketBrian L. Frank for The New York TimesThe F.D.A. points out that the thymosin-alpha 1 peptide therapy is not authorized in the United States to treat Covid-19, nor is it approved for any other condition. Over the past year, that agency and the Federal Trade Commission have cracked down on hundreds of companies making unsupported claims about supposed Covid-19 treatments, including thymosin-alpha 1, BPC-157 and vitamin C infusions. The F.T.C. warns that anyone who makes “deceptive claims related to the treatment, cure, or prevention of Covid-19” could be subject to penalties of up to $43,792 for each violation.Neither of those agencies has sent a public warning letter to Dr. Guzman. He and his lawyer did not respond to several requests for comment.Dr. Juan G. Bautista, who works with Dr. Guzman at the clinic, declined to comment on his colleague. “I don’t want to speak against another doctor if their intention was to take care of a patient,” he said.When Dr. Bautista came down with Covid-19 himself last year, he tried peptides, along with a host of standard treatments. He said that he hadn’t used peptides to treat Covid-19 in his patients but that he didn’t fault doctors who had used experimental therapies that they believed could help people recover from a never-before-seen virus.“Physicians were doing everything possible to keep patients outside of the hospital,” he said, citing the distress of intubation and medical bills that could wipe out the savings of his low-income patients from Fresno and the broader San Joaquin Valley. “There’s not a lot of people here in the Valley that take care of the poor.”Sandy Sirias contributed reporting. This story was supported by the Pulitzer Center.