One-third of Americans are taking prescription and over-the-counter drugs, such as birth control pills, antacids and common heart medications, that may raise the risk of depression, researchers warned on Tuesday.

Since the drugs are so common, people may be unaware of their potential depressive effects, said the report in the Journal of the American Medical Association (JAMA).

"Many may be surprised to learn that their medications, despite having nothing to do with mood or anxiety or any other condition normally associated with depression, can increase their risk of experiencing depressive symptoms, and may lead to a depression diagnosis," said lead author Dima Qato, assistant professor of pharmacy systems, outcomes and policy at the University of Illinois at Chicago.

The report was released one week after US health authorities said suicides have risen 30 percent in the past two decades, with about half of suicides among people who were not known to have mental illness.

For the current study, researchers found that the risk of depression was highest among people who were taking more than one drug with depression as a possible side effect.

"Approximately 15 percent of adults who simultaneously used three or more of these medications experienced depression while taking the drugs, compared with just five percent for those not using any of the drugs, (and) seven percent for those using one medication," said the study.

Anti-depressants are the only drug class that carries an explicit warning -- called a black box warning -- of suicide risk.

For other common medications -- like blood pressure lowering pills, antacids known as proton pump inhibitors, painkillers and hormonal contraceptives -- the warnings are harder to find or simply don't exist in the packaging.

"Product labeling for over-the-counter medications does not include comprehensive information on adverse effects including depression," said the report.

"Many patients may therefore not be aware of the greater likelihood of concurrent depression associated with these commonly used medications."