Tampa (AFP) - 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 suffer from 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.

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

- 200 drugs -

Researchers found that more than 200 commonly used prescription drugs have depression or suicidal symptoms listed as potential side effects.

Use of prescription drugs with suicidal thoughts listed as a potential adverse effect increased from 17 percent in 2005 to 24 percent a decade later, the study said.

For drugs with depression as a possible side effect, use increased from 35 percent in 2005 to 38 percent in the 2013 to 2014 period.

"Use of antacids with potential depression adverse effects, like proton pump inhibitors and H2 antagonists, increased from five percent to 10 percent in the same period," said the study.

"Use of three or more drugs concurrently increased from seven percent to 10 percent."

- Limits, solutions -

The study was observational in nature, and was based on survey data on more than 26,000 adults from 2005 to 2014, collected as part of the National Health and Nutrition Examination Survey.

Researchers cautioned that the survey approach meant conclusions could not be drawn about cause-and-effect, and that questionnaires did not account for a history of depression.

According to Allan Young, director of the Center for Affective Disorders at King's College London who was not involved in the study, the "findings seem robust."

"This confirms the well-known fact that these medications might be causing depression in some people and we should be on the look-out for that so that we can detect and then manage the depression," Young said.

"Many prescription medicines may have depression as a possible side effect and this should be discussed with patients up front."

Lead author Qato said solutions could include updating drug safety software so pharmacists could recognize if a person is taking drugs that raise the risk of depression.

"With depression as one of the leading causes of disability and increasing national suicide rates, we need to think innovatively about depression as a public health issue, and this study provides evidence that patterns of medication use should be considered in strategies that seek to eliminate, reduce or minimize the impact of depression in our daily lives," she said.