The basis of both authorization systems is the categorisation of medical devices in different classes. Devices in higher risk classes are subject to more stringent conformity assessment procedures to obtain market authorization. An important difference between the two systems is that the market authorization procedures in the USA are performed entirely by the government (Food and Drug Administration), while in Europe these are performed by companies (Notified Bodies) designated and supervised by the government. Another difference is that Europe has a strict set of rules to categorise the devices in their risk classes, while the USA follows a much more diffuse approach.
In both Europe and the USA, the systems have been criticized with regard to guaranteeing safety and effectiveness of medical devices on the market. An important focus of the criticism has been on products obtaining market authorization by using safety and effectiveness data of existing products on the market. The manufacturers claim equivalence between their product and the existing product. This way, they need to generate significantly less data on their own product to substantiate safety and effectiveness. This is possible in the USA as well as in Europe.
Recent examples of products that were allowed on the market through both systems using equivalence, and that have led to unexpected adverse effects, are metal-on-metal hip implants and transvaginal meshes. In response to this type of problems, improvements for both systems are being proposed, which are partially implemented. As an example in Europe,requirements for Notified Bodies have been made more stringent and their supervision has been intensified.