A medical device is an instrument, apparatus, implant, in vitro reagent, or similar or related article that is used to diagnose, prevent, or treat disease or other conditions, and does not achieve its purposes through chemical action within or on the body (which would make it a drug).edical machine, contrivance, implant, in vitro reagent, or other similar or related article, including a component part, or accessory that is: 1  Recognized in the official National Formulary, or the United States Pharmacopoeia, or any supplement to them.