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What are Clinical Trials?

What Are Clinical Trials?

A critical part in the process of bringing new therapies to patients is clinical development, the study of potential new therapies in humans.

It typically takes 12 years from the moment of discovery in the lab for a potential new therapy to gain approval for use and reach patients. Clinical development is the most time intensive and expensive part of this research and development continuum accounting for approximately 45 to 75 percent of the $1.2 billion average cost of bringing a new therapy to market.

Trials conducted during clinical development generate thousands of pieces of data and are generally used by regulatory agencies, such as U.S. Food and Drug Administration (FDA) to determine approval for use of the therapy, and in which medical indications.

Helping Patients

Clinical trials involve hundreds to many thousands of volunteer trial participants. Every trial is governed using well-defined ethical rules and standards to protect participant safety.

For patients suffering from a condition that is currently untreatable, participation in a clinical trial may provide access to potential new therapies. While participating, volunteers obtain closely controlled care in research medical facilities, in addition to helping others by contributing to medical research.


Phases of Development

Clinical Development Process

An experimental therapy is first tested in the laboratory and in animal studies. After this “pre-clinical” testing, and only if shown to meet certain safety criteria and have value as a potential new therapy, the candidate advances to clinical testing in humans. The Phases of Clinical Development

Phase 1

Phase 1 clinical trials mark the first time an experimental therapy is administered to humans. Phase 1 trials usually focus on ensuring the therapy is safe to use in people, rather than how effective it may be as a treatment for a given disease. During this phase, escalating doses of the experimental therapy are given to a small number of study participants so that researchers can measure the body’s response, including how it is absorbed, its duration in the blood stream and which dosage levels are safe and well tolerated.

Phase 2

Phase 2 trials generally assess the effectiveness of an experimental therapy at treating a specific illness or medical condition. Information about the experimental therapy's safety, side effects and potential risks are also collected. In this phase, researchers work to determine the most effective dosages for the experimental therapy and the most appropriate method of delivery, such as tablets, extended release capsules, infusions or injections. Phase 2 clinical trials involve a larger number of trial participants, typically up to several hundred, who usually have the medical condition that the experimental therapy is intended to treat.

Phase 3

Phase 3 trials test the results of earlier trials in much larger groups of people and gather additional information on the effectiveness and safety of the experimental therapy. This phase will usually involve several hundred to several thousand participants across multiple study locations. These trials are often randomized, where participants are arbitrarily allocated to receive the experimental therapy, placebo or another therapy (a “comparator”), and “double-blinded,” in which neither the investigator nor the participant are aware if the therapy given is the true experimental therapy, placebo (medication with no active ingredients) or another therapy (a “comparator”). Phase 3 trials generally provide the primary basis for the benefit-risk assessment for the new therapy and much of the core information about the therapy that is analyzed for inclusion in final labeling if approved by the regulatory authority.


Filing an application for registration with the country’s health regulatory authority is the next step in bringing a potential new therapy to patients. In the U.S., a New Drug Application (NDA) is filed with the U.S. Food and Drug Administration (FDA). In Europe, a Market Authorization Application (MAA) is filed with the European Agency for the Evaluation of Medicinal Products (EMEA). A description of the therapy's manufacturing process along with quality data and trial results from all pre-clinical and clinical trials are provided in order to demonstrate the safety and effectiveness of the new therapy. If approval is granted, the new therapy can then be sold for use as detailed in the final approval label granted by the regulatory authority.

Phase 4

Phase 4 trials — also called "post-marketing studies" — are conducted after regulatory approval and are critical to informing the ongoing use of the therapy. Through such trials, researchers collect additional information about longer-term risks, benefits and optimal use. These trials often involve thousands of participants and may continue for many years.

Visit to learn more about Pfizer's Post Marketing Commitments.

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