The average physician in the survey identified the F.D.A. approval status correctly for only about half the drugs on a list provided by the researchers, according to a study in Pharmacoepidemiology and Drug Safety.

Confusion was greatest with psychiatric drugs, the survey of some 600 doctors found. Nearly one in five who prescribed Seroquel (quetiapine) in the previous year thought it was approved for patients with dementia and agitation, even though it was never approved for this use and even carried a “black box” warning that it was dangerous for elderly patients with dementia. And one in three doctors who used lorazepam (often marketed as Ativan) to treat chronic anxiety thought it had been approved for this use; in fact, the F.D.A. warning advises against using it for this purpose.

The study’s senior author, Dr. G. Caleb Alexander, assistant professor of medicine at the University of Chicago, said a concern was that off-label uses often did not have the same level of scientific scrutiny as F.D.A.-approved uses.