While there is much to consider when bringing an OTC drug to market, it is helpful to start with the concept of a "drug" versus a "new drug."
In general, a drug is considered a "new drug" (which will require a product specific application to be approved by FDA) if it is not generally recognized, among experts qualified by scientific training and experience to evaluate the safety and effectiveness of drugs, as safe and effective for use under the condition prescribed, recommended, or suggested in the labeling. This is irrespective of whether it is an OTC or a prescription drug.
When is a drug not considered a "new drug?"