The Food and Drug Administration (FDA), a regulatory agency within the Department of Health and Human Services, regulates the safety and effectiveness of drugs sold in the United States. FDA divides that responsibility into two phases. In the preapproval (premarket) phase, FDA reviews manufacturers' applications to market drugs in the United States; a drug may not be sold unless it has FDA approval. Once a drug is on the market, FDA continues its oversight of drug safety and effectiveness. That postapproval (postmarket) phase lasts as long as the drug is on the market. Beginning with the Food and Drugs Act of 1906, Congress and the President have incrementally refined and expanded FDA's responsibilities regarding drug approval and regulation. The progression to drug approval begins before FDA involvement. First, basic scientists work in the laboratory and with animals; second, a drug or biotechnology company develops a prototype drug. That company must seek and receive FDA approval, by way of an investigational new drug (IND) application, to test the product with human subjects. It carries out those tests, called clinical trials, sequentially in Phase I, II, and III studies, which involve increasing numbers of subjects. The manufacturer then compiles the resulting data and analysis in a new drug application (NDA). At that point, FDA reviews the NDA with three major concerns: (1) safety and effectiveness in the drug's proposed use; (2) appropriateness of the proposed labeling; and (3) adequacy of manufacturing methods to assure the drug's identity, strength, quality, and purity. The Federal Food, Drug, and Cosmetic Act (FFDCA) and associated regulations detail the requirements for each step. FDA uses a few special mechanisms to expedite drug development and the review process when a drug might address an unmet need or a serious disease or condition. Those mechanisms include accelerated approval, animal efficacy approval, fast track designation, breakthrough therapy designation, and priority review. Once FDA has approved an NDA, the drug may enter the U.S. market, but FDA continues to address drug production, distribution, and use. Its activities, based on ensuring drug safety and effectiveness, address product integrity, labeling, reporting of research and adverse events, surveillance, drug studies, risk management, information dissemination, off-label use, and direct-to-consumer advertising, all topics in which Congress has traditionally been interested. FDA seeks to ensure product integrity through product and facility registration; inspections; chain-of-custody documentation; and technologies to protect against counterfeit, diverted, subpotent, adulterated, misbranded, and expired drugs. FDA's approval of an NDA includes the drug's labeling; the agency may require changes once a drug is on the market based on new information. It also prohibits manufacturer promotion of uses that are not specified in the labeling. The FFDCA requires that manufacturers report to FDA adverse events related to its drugs; clinicians and other members of the public may report adverse events to FDA. The agency's surveillance of drug-related problems, which had primarily focused on analyses of various adverse-event databases, is now expanding to more active uses of evolving computer technology and links to other public and private information sources. The FFDCA allows FDA to require a manufacturer to conduct postapproval studies of drugs. The law specifies when FDA must attach that requirement to the NDA approval and when FDA may issue the requirement after a drug is on the market. To manage exceptional risks of drugs, FDA may also require patient or clinician guides and restrictions on distribution. The agency publicly disseminates information about drug safety and effectiveness; and regulates the industry promotion of products to clinicians and the public.