In 1968, the FDA commissioned the Drug Efficacy Study Implementation (DESI) that identified 3,400 active drug ingredients marketed between 1938 and 1962 that were safety tested but not proven effective. The FDA explains that
"One of the early effects of the DESI study was the development of the Abbreviated New Drug Application (ANDA). ANDAs were accepted for reviewed products that required changes in existing labeling to be in compliance. In September 1981 final regulatory action had been taken on 90% of all DESI products. By 1984, final action had been completed on 3,443 products; of these, 2,225 were found to be effective, 1,051 were found not effective, and 167 were pending."Federal law permits the manufacturer to continue to market DESI drugs until the FDA deems the drug unapproved based on lack of efficacy following notice and a hearing.
Forty years later, the FDA has not completely closed the loop on these DESI drugs. The FDA's web site explains that
For a variety of historical reasons, some drugs, mostly older products, continue to be marketed illegally in the United States without required FDA approval. Many healthcare providers are unaware of the unapproved status of some drugs and have continued to unknowingly prescribe unapproved drugs because the drugs’ labels do not disclose that they lack FDA approval. Often these drugs are advertised in reputable medical journals or are included in widely used pharmaceutical references such as the Physicians’ Desk Reference (PDR).The FDA recently released compliance guidance on unapproved drugs and plans a workshop in January 2007.
BNA reports that Sen. Charles Grassley (R - Iowa), Chairman of the Senate Finance Committee, is concerned that the compliance guidance "estimates that there are several hundred unapproved active ingredients in drugs currently on the market", and he is pressuring the agency to remove these drugs from the market.