Products are not considered medical devices if they have general utility but are neither dedicated to, nor intended or promoted for, medical applications. For example, a screw is considered a medical device if it is promoted for holding bones together rather than holding pieces of wood together. Distinguishing between drugs and devices is also sometimes difficult. Medical devices, unlike drugs, do not achieve their principal action through chemical action or metabolization in or on the body. For example, plaster cast used for bone healing is considered a device, whereas a topical ointment used to promote bone healing is considered a drug.
Combination products have both drug and device components.
The mechanism of principal action determines which center regulates it. Bone cement with an antibiotic, for example, is considered a device.