A new Tufts Center for the Study of Drug Development report reveals that drugs to treat central nervous system (CNS) disorders take longer to develop and are rejected by the U.S. Food and Drug Administration (FDA) at a higher rate than other drugs. The U.S. approval rate for CNS compounds is “less than half that of all other compounds,” and the “overall clinical approval success rate for CNS compounds first tested in human subjects from 1995 to 2007 was 6.2%,” compared to 13.3 percent for non-CNS drugs. The mean clinical development time for CNS drugs approved in the United States from 1999-2013 was 18 percent longer than that for non-CNS drugs, and FDA takes longer to approve CNS drugs than non-CNS drugs.

Still, the report found that approval rates for CNS drugs have held steady and accounted for about one in 10 of all U.S. approvals since the 1980s. According to the report, CNS disorders are not only diverse, but they are challenging to treat. They include depression, psychosis, epilepsy, and Alzheimer’s disease. As chronic conditions with complex pathologies, these disorders are also a challenge to measure objectively, so determining whether a drug has worked in a clinical trial can be problematic. See Tuft University News Release, November 4, 2014.