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A promising therapy for certain food allergies may be riskier than hoped, according to a new review. It found that patients with a peanut allergy given oral immunotherapy—a treatment that exposes them to small doses of the food over time—were more likely to experience life-threatening allergic reactions like becoming unable to breathe and other serious symptoms like vomiting than those who were given placebo or avoided their triggers.

Oral immunotherapy has emerged as a hopeful treatment for food allergy in recent years. Its basic premise is similar to the allergy shot people get for their pet or pollen allergy. Over a period of months, at the doctor’s office, patients eat a gradually increasing but small dose of peanut that ideally shouldn’t cause any reaction or only mild symptoms. Eventually, people can take those doses, which can come as a powder, pill, or even peanut butter, at home as maintenance to keep their tolerance up.

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Even in people who respond well to the treatment, it isn’t seen as a cure. People still have to watch what they eat and hold on their supply of epinephrine to treat a serious allergic reaction, also known as anaphylaxis. Symptoms of anaphylaxis can range to hives to swelling of the throat so severe that it can suffocate you. 

But it is supposed to significantly desensitize people to their trigger and lower their risk of anaphylaxis. Human trials of oral immunotherapy are ongoing, and have begun to reach phase III clinical research—the final threshold before a treatment can win approval from the Food and Drug Administration.

Individually, these trials seemed to have been very successful, with anywhere from 60 to 80 percent of patients becoming desensitized. But the researchers behind this current review, published in the Lancet, decided to look at the big picture. They reviewed 12 randomized trials, involving more than 1,000 volunteers with an average age of nine, that compared people who took oral immunotherapy for their peanut allergy to those who didn’t. These trials, three of which have yet to be published, covered the period of time that patients built up their tolerance and then tried to maintain it.

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As with the individual trials, they found people on the treatment did largely become more tolerant to peanuts. But their risk of self-reported anaphylaxis was threefold higher compared to people who didn’t take the therapy (22.2 percent vs 7.1 percent), while their risk of needing epinephrine was about doubled (3.7 percent vs 8.2 percent), as was their risk of other serious symptoms like vomiting (6.2 percent vs 11.9 percent). Equally worrying was that people’s quality of life didn’t improve at all when compared to the control group.

“It shows that current peanut oral immunotherapy regimens can achieve the immunological goal of desensitization, but that this outcome does not translate into achieving the clinical and patient desired aim of less allergic reactions and anaphylaxis over time,” said lead author Derek Chu, an immunologist at McMaster University in Canada, in a statement.

One issue may be that once patients stop getting their treatments under the watchful eye of their doctor, the challenges of real life can complicate their response to it. Anything from a hot shower to a cold bug can affect a person’s immune system, and therefore their response to the treatment.

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Chu and his team don’t think that oral immunotherapy is worthless, though. For some people, it may be worth the risk of getting sick from your dose taken at home if it means a higher tolerance to peanuts accidentally encountered in a restaurant. There’s also still the possibility that the treatment might, over the long term, lead to less allergic reactions to peanuts than you’d typically expect from someone just trying to avoid peanuts.

“Our results do not denounce current research in oral immunotherapy, but the method needs to be more carefully considered, improvements in safety made, and measures of success need to be aligned with patients’ wishes,” said Chu.

The rate of food allergies in America and elsewhere has continued to increase over time. It’s estimated that 32 million Americans currently have a food allergy, while a study in 2018 found that almost 2.5 percent of children currently have a peanut allergy. And while exposing people at risk of peanut allergy to the food in their first years of life lowers their chances of developing it, there is no current treatment for peanut allergy once you have it.

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