When a doctor prescribes a drug to someone, they take careful note of the active compound and the dosage, but they are much less likely to think about the inactive ingredients.
Even drugs with the same active chemical at the same dosage can have different ingredients, depending on who manufactured them. For instance, the authors note that 43 different companies produce a total of 140 distinct formulations of levothyroxine, a treatment for thyroid hormone deficiency.
Also, although manufacturers provide a list of ingredients on the packet, it might not be clear from the chemical names which of them could contain allergens. For instance, the packet would not label a wheat derivative as containing gluten.
Most people will only consume small quantities of these inactive ingredients, but some groups, such as older adults, tend to take more medications.
They found that, in most cases, more than half of each pill consists of inactive ingredients. In some cases, they considered as much as 99 percent of the pill to be nonpharmaceutical.
Worryingly, they discovered that 93 percent of medications contain allergens, including lactose, dyes, and peanut oil. Almost all medicines contain ingredients that some people might not be able to tolerate, such as gluten.
More than half of medications contain FODMAP sugars that trigger digestive problems in some individuals with irritable bowel syndrome.
Although drugs that contain peanut oil always come with a warning on the packaging, the same is not true for any of the other ingredients. Making sense of the ingredients is challenging, and even if someone manages to spot an allergen in their pills, there is no guarantee that they will be able to find a version of the medicine that does not include the allergen.
The authors of the study hope that their findings will raise awareness of this issue. Globally, allergies appear to be becoming more common, making this type of research more important than ever.
In the future, the researchers believe that there is a need for new regulations requiring companies to provide detailed information on inactive ingredients.