Is a drug gluten free or not? The best way to determine if a drug is gluten free is by calling the manufacture. Both over-the-counter and prescription drugs can be a hidden source of gluten. Labeling gluten containing ingredients isn’t required of drug manufacturers and it’s often in inactive ingredients like fillers. Do your due diligence and call your drug manufacturers or have your pharmacist call. Don’t rely on what you think you know and what others claim to know. Call the professionals and triple check to make sure you know everything you are ingesting is gluten free.