Moving a drug through the drug development process takes time and an abundance of testing. On average, it takes 10-15 years for a drug to complete the journey from the laboratory through the FDA drug approval process. What happens along the way is a complex, precise set of hurdles and tests that a drug must pass before it is deemed safe and effective for treating a condition.
After a drug is discovered or created and deemed worthy of further investigation, extensive laboratory and animal tests are the first order of business. This step in the process, called pre-clinical testing, can take up to 6 years. In animal testing, researchers are looking to see what effects—both beneficial and harmful—a drug may have in a living organism.
If pre-clinical testing issues positive results, a drug will move on to clinical testing in humans. All new drugs must pass through 3-4 orderly phases of clinical testing. The FDA does not conduct the clinical trials. Instead, it requires the drug’s manufacturers to perform increasingly rigorous tests designed to gain information about the drug’s efficacy and safety, while at the same time protecting those involved in the study. Each facility where the study is performed has its own objective drug safety review board that oversees the trial. Its job is to determine the specifics of how the study is conducted, monitor patients for side effects, and ensure patient safety. The FDA can put a hold on clinical testing at any point in the process if it believes a study is unsafe. It can mandate that a test be repeated, expanded, or that an additional clinical study is required before approval. The FDA is under no legal obligation to approve any drug or treatment.
In Phase I clinical testing, a relatively small number of volunteers, perhaps 20-80 people, receive the drug with the primary goal of determining whether it is safe to use in people. Usually, several different treatment doses and/or strategies are tested. Phase I tests usually require about 1-2 years to complete.
The goal of Phase II clinical testing is to continue testing safety while looking for the first signs of whether the drug offers any benefits. Anywhere from a 100-300 patient volunteers participate in these 2-year phase II trials. Some trials are controlled, meaning that those taking the test drug are compared to those taking a placebo (disguised to appear the same as the treatment) or a standard treatment for the disease. These volunteers are often not responding to current treatments or are seeking an alternative approach to treatment.
Phase III clinical tests are the most rigorous of all—their goal is to monitor side effects and efficacy with long-term use. The FDA reviews this phase of clinical testing most closely in order to decide whether a drug should be approved. Usually, about 1,000-3,000 volunteer patients are involved in a Phase III clinical test.
Phase III clinical tests can take up to 3-4 years to complete. Upon completion, the clinical data is extensively analyzed and compared to see what benefits the drug offers and any harmful side effects. If Phase III clinical results show a drug’s benefits outweigh its side effects, it is then formally submitted to the FDA, which will decide its fate. Also, different dosages, populations, and combinations with other medications are evaluated during this time. On average, the FDA may take an additional 1-2 years to review the clinical testing information before deciding whether a drug is safe and effective and worthy of marketing approval. During this time, it pays special attention to the recommendations of its advisory committees—groups of FDA experts with particular expertise in the condition the drug is intended to treat.
Clinical testing does not necessarily stop once a drug is FDA-approved. Post marketing surveillance trials are conducted to learn more about the drug’s long-term risks, benefits, and optimal use, or to test the product in different groups of people.
Rarely, the results of these trials may cause a drug to be voluntarily withdrawn from the market by its manufacturer. In other cases, the FDA issues a warning letter to healthcare professionals about newly discovered information about a drug or, if necessary, revokes the drug’s marketing license outright after its approval. More commonly, though, these trials support earlier findings and may add important cautionary information about use with other medications or in the presence of other conditions.
The FDA timeline can be flexible in the face of serious or life-threatening conditions without treatments that work. Drug effectiveness may not be measured only on its clinical benefits (how a patient feels, functions, or survives) because they have not been fully studied. Instead, the FDA looks at other aspects of the drug, like lab results, to predict its long-term benefit. This has been done with HIV and cancer drugs. The value of an antiretroviral drug may be determined by how much it lowers HIV blood levels. The short-term benefit of lower HIV blood levels may translate into someone getting better or living longer. The drugs trials are still put through the normal steps during this process, but the accelerated process may help those who need it most.
The drug development and approval process. FDA Review website. Available at:
Accessed December 30, 2016.
The FDA's drug review process: Ensuring drugs are safe and effective. US Food and Drug Administration website. Available at: http://www.fda.gov/drugs/resourcesforyou/consumers/ucm143534.htm. Updated November 6, 2014. Accessed December 30, 2016.
Last reviewed December 2016 by Michael Woods, MD
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