The "off-label" prescribing is a legal, common practice that is raising questions because of the lack of scientific evidence supporting its safety and effectiveness, USA Today reported Tuesday.

"Although previous research has highlighted the substantial frequency of off-label drug use without good evidence, we have identified and prioritized specific drugs warranting attention," authors of the study wrote in the journal Pharmacotherapy.

Fourteen drugs, including Celebrex, a pain drug, and Zoloft, an antidepressant, were listed as having the greatest need for research, the study by the Stanford Prevention

Research Center indicated. Researchers considered three factors when they developed their list -- volume of off-label use with inadequate evidence, drug safety, and cost and market considerations, the newspaper reported.

"It's not that these off-label uses are necessarily harmful or that these drugs don't work," senior author Randall Stafford, associate professor of medicine at the center, told USA Today. The problem, he said, is that no one can be certain of the outcome, because studies haven't been done.

The FDA requires drug companies to test their drugs only against conditions for which they're seeking approval.