The Human Factor Study produces combined devices or products which combine a device, drug or biological element which is totally different from the conventional method. As mentioned by the given link the combined products are formed by three different ways.
1) Physically or chemically combined
2) Co-packaged
3) Separately distributed with specific labeling to combine the products during the use
This leads to the complexity of the product so when the usage of the combined products comes, it must be carefully implemented than the development of the product. This makes even the development and implementation both as a complicated process.
For successful implementation of a combined product certain important things must be considered.
1) Time and sequencing of study in relation to study and combination of product
2) Benefits of Human Factor study related to the product when compared with other normal clinical process
3) Changes of a combined product should be proved by proper human factor study
4) Information provided to the FDA must satisfy the needs for this combined product

– Akshaya Kirithy Baskar

http://blogs.fda.gov/fdavoice/index.php/2016/03/addressing-issues-relating-to-combination-products-human-factors/