WASHINGTON - A new report says pills can contain ingredients like gluten, lactose or allergy-triggering dyes that may cause problems for certain patients.

Boston researchers began studying so-called "inactive" ingredients after a patient with celiac disease who's supposed to avoid gluten received a prescription drug containing it.

The extra ingredients are safe for most people, added to drugs to do things like improve absorption or taste. But Wednesday's report cited rare allergic reactions and said it's hard for patients who are sensitive to certain compounds - or even their doctors - to learn if a drug contains something they should avoid.

The issue already is getting some attention. A Food and Drug Administration proposal recommends gluten labeling for drugs.

The report was published in Science Translational Medicine.