Investigators found it took about seven months to issue a warning and another four months to solve the problem.

Sen. Charles Grassley says the FDA does not have a department that exclusively monitors such abuses and as a result, Medicare and Medicaid may be paying out billions of dollars for medications that may well be useless, if not harmful to the patients taking them.

The FDA “isn’t keeping track of how drugs are marketed for off-label use, even though marketing for off-label use is illegal and it’s the FDA’s job to enforce that law,” Grassley said in a statement. “As a result, drug makers aren’t being held accountable for promoting unapproved use of medicine and patient safety is diminished.”

A previous study in 2006 found that as many as 20 percent of prescriptions are written for off label use.

Investigators say the problem is further compounded by the fact that while drug companies are forbidden from promoting off label use of a drug, guidance proposed in early 2008 says they can provide doctors with research that suggests such unapproved use. Under current law, doctors are not forbidden from prescribing an off label use for medications.