Once the Clinical Trial phases are over, it waits for FDA Center for Drug Evaluation and Research (CDER) approval. Only after the CDER's approval, the safest drug is permitted to sell via prescription or OTC in the United States. The results are segregated, and the final documentation is done. Those results are forwarded to CDER, which assigns a team of doctors, chemists, pharmacologists, and other scientists to review the evidence. The FDA does not conduct any further tests; they rely on the clinical trials performed by the pharmaceutical houses and sponsors.

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The FDA designated panel goes through the detailed documentation of clinical trials and studies the action and reaction of drugs, and then finally, it is taken into account for the drug approval process. The review team analyzes the results of the study. The team also looks for possible issues, if any, with the application, including the weaknesses of the study design. Reviewers determine whether they agree with the results and conclusions of the sponsors, or whether they require some additional information for making a decision. Each reviewer has to prepare a written evaluation that contains recommendations and findings regarding the application. These evaluations are then considered by office directors, division directors, and team leaders, based on the type of request.

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Generally, the process is lengthy, and the minute details are studied because it is the question of the mass population. The FDA requires to be fully satisfied before giving it a green signal to ride in the market. Two things are taken into consideration; the efficacy of the drug outweighs the risk associated with the drug, and the drug works efficiently as per the claim of the pharmaceutical companies.

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According to the Prescription Drug User Fee Act (PDUFA), 1992, there is a two-tiered system – Priority Review and Standard Review. Review applies to drugs offering a minor improvement over market therapies that already exist, and the amendments made to PDUFA in 2002 established a 10-month goal for a standard review. Priority Review designation is given to drugs that offer significant advances in treatment or provide a treatment where nothing exists. Accelerated approval is given to some new drugs for severe and life-threatening illnesses that lack satisfactory treatments. Six months' time is set for completing a Priority Review.

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For protecting the rights and welfare of people involved in clinical trials, and for verifying the integrity and quality of information submitted, the FDA's Division of Scientific Investigations (DSI) is instructed to conduct inspections of the study sites of clinical investigators. If they are satisfied after going through several investigation processes, the approval is given for the drug to market in the USA. If any deviation is detected, the FDA issues a complete response letter, and the sponsor has to submit the required deficiencies to move for approval.