American researchers have identified 14 widely prescribed drugs that are used for other conditions than the ones found on their labels, a phenomenon known as “off-label” prescribing. It is an unsafe practice as there is little evidence that using a drug for an unapproved purpose is always beneficial or safe, the study published in the Nov. 24 issue of the journal Pharmacology says.

“Off-label prescribing is not based on the same level of evidence as on-label prescribing,” study lead researcher Surrey Walton, an assistant professor of pharmacology administration at the University of Illinois at Chicago, said.

Three factors were considered when making the list: the volume of off-label use with inadequate evidence, drug safety, and cost and market considerations.

The most widely prescribed are antidepressants and antipsychotic the study found. At the top of the list is the antipsychotic quetiapine (Seroquel), which is approved as a treatment for schizophrenia. The study found that off-label use of this drug accounted for 76 percent of its prescriptions.

Seroquel is followed by blood thinner warfarin, used off-label to treat hypertensive heart disease, the antidepressant escitalopram (Lexapro), used off-label to treat bipolar disorder, the schizophrenia drug risperidone (risperdal), used off-label to treat bipolar disorder and the asthma drug montelukast (Singulair), used off-label to treat chronic obstructive pulmonary disease.

Rounding the list were: depression drugs bupropion (Wellbutrin), sertraline (Zoloft), venlafaxine (Effexor), duloxetine (cymbalta), trazodone (desyrel), joint sprain/strain drug celecoxib ( Celebrex), high blood pressure drug lisinopril (Prinivil, Zestril), schizophrenia drug olanzapine (Zyprexa) and chronic renal failure drug epoetin alfa (Procrit, Epogen).

 The problem with these drugs is not necessarily linked to their efficiency, because they might work in most of the cases. The problem is that no one can be certain, because needed studies haven’t been done to prove that.

“Off-label prescribing means that we're venturing into uncharted territory where we lack the usual level of evidence presented to the FDA that tells us these drugs are safe and effective,” said Randall Stafford, MD, PhD, associate professor of medicine at the Stanford Prevention Research Center, who is the senior author of the study.