Over 90% Of Medications May Contain Allergens In Their Inactive Ingredients, But Here’s Why You Shouldn’t Worry

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Many of us take prescription medications regularly — from anti-depressants to migraine treatments — and we often assume that what's in them is just whichever ingredients are doing the work. However, a new study in Science Translational Medicine has found that the inactive ingredients in many oral medications can contain allergens, or substances that can irritate the immune system — over 90 percent of them, in fact. "A majority of medications contain ingredients that could cause adverse reactions," the study says. But the keyword here is "could" — meaning, if you don't have a known allergy to these ingredients, it's probably not something you have to worry about.

Inactive ingredients themselves aren't meant to be the star players in your drugs; the scientists behind the study explained that they're meant to "enhance [the] physical properties" of active ingredients. For instance, citalopram, a common anti-depressant, contains the "active" ingredient citalopram hydrobromide, and a wide range of inactive ones, including corn starch, glycerin, polyethylene glycol, and copolyvidone, to help with digesting the pill. However, there may be ingredients in that inactive list that may cause you some grief.

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The study looked at over 42,000 recipes for legal medications in the U.S., and found that 92.8 of them contained ingredients that could potentially be allergens and are known to cause allergic reactions, like peanut oil, lactose, or dye. Over 50 percent contained FODMAPs, a kind of carbohydrate that may have negative effects on the digestion of people with irritable bowel syndrome. These ingredients could hamper how some people react to their medications.

"For most patients, it doesn't matter if there's a little bit of lactose, a little bit of fructose, or some starch in there. However, there is a subpopulation of patients, currently of unknown size, that will be extremely sensitive to those and develop symptoms triggered by the inactive ingredients," one of the study's authors, Dr. Daniel Reker, said in a press release.

Part of the issue, fellow study author Dr. Giovanni Traverso told Science News, is that there's a lack of clarity in prescribing practices. "The healthcare provider doesn’t really know which formulation the patient is going to receive, because that’s generally governed by the pharmacy," he said. If your doctor prescribes something and doesn't explicitly mention that you're allergic or sensitive to a particular substance, the pharmacy won't know and won't check the inactive ingredients of the drugs they give you (which is why it's important to ask!).

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It's always possible to find what inactive ingredients are in your medication; just check out the ingredients list or ask your pharmacist. For another, just because something may contain an allergen doesn't mean you'll react to it, or that you'll ingest enough to cause a reaction. “For some of these ingredients, we have a sense of how much is sufficient to elicit an intolerance or an allergy," Traverso explained. "But for some of these other sugars, we have less of a sense. Part of the future work is really trying to dive into this, and understand how much for an individual is too much."

It's also possible for people to believe they're sensitive to something and not actually have an issue. Allergist Dr. John Kelso told NPR in response to the study that, in some cases, worries about allergies to inactive ingredients come to nothing. "Oftentimes [medications] are being withheld from patients who say they're allergic to eggs or soy or something else that may be in the medication, but it is actually not a problem," he said. Penicillin is a unique example: many people believe they have an allergy to it, but Kelso says, "We realized lately that approximately 95 percent of patients who are labeled penicillin-allergic are not."

Want to make sure you're getting the best medications for you? If you've got an intolerance or allergy to something specific — a gluten intolerance or a bad reaction to certain sugars, for instance — or have digestive issues that may interfere with absorbing oral medications, your doctor needs to know.