The FD&C Act defines drugs as "articles intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease" and "articles (other than food) intended to affect the structure or any function of the body of man or other animals". FDA's Center for Drug Evaluation and Research (CDER) is evaluating and approving new drugs before they are sold in the US. It has responsibility for both prescription and nonprescription or over-the-counter (OTC) drugs.
Companies must submit a New Drug Application (NDA) to introduce a new drug product into the U.S. Market. New drugs, like other new products, are frequently under patent protection during development. The patent protects the sponsor's investment in the drug's development by giving them the sole right to sell the drug while the patent is in effect.
When the patents or other periods of exclusivity on brand-name drugs expire, manufacturers can apply to the FDA to sell generic versions. For this the sponsor must submit an Abbreviated New Drug Application (ANDA).
OTC drugs can be brought to the market following the NDA process or under an OTC monograph. Each OTC drug monograph is a kind of "recipe book" covering acceptable ingredients, doses, formulations, labeling, and, in some cases, testing parameters. OTC drug monographs are continually updated to add additional ingredients and labeling as needed. Products conforming to a monograph may be marketed without FDA pre-approval.