People taking a widely used class of antidepressants known as SSRIs may find the benefits of the medication cancelled out when they also take painkillers such as ibuprofen, scientists say.

The findings from experiments in mice can't prove that drugs such as ibuprofen and Aspirin — known as non-steroidal anti-inflammatory drugs, or NSAIDs — stop antidepressants from working, the researchers said.

But the possible effect is worth considering, since a similar effect was found analyzing data from a human study, the researchers say in this week's online issue of the Proceedings of the National Academy of Sciences, or PNAS. 

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NSAID painkillers may prevent a class of antidepressants from working effectively. (iStock)

"Analysis of our clinical data strongly suggests that remission rates among depressed individuals may be improved by avoiding certain common over-the-counter medications," Paul Greengard of Rockefeller University in New York and his co-authors wrote.

Mice treated with an SSRI antidepressant behaved differently when they were also given the anti-inflammatory painkillers, scientists found. The animals performed worse on tests measuring their stress and depression than those that took just the antidepressant.

Tests showed mice treated with the antidepressant citalopram and an NSAID also had lower levels of the antidepressant in their blood than those taking the antidepressant alone.

The researchers then analyzed data on a previous study of 1,546 Americans treated with citalopram for 12 weeks, comparing remission rates for depressive symptoms among those taking just the antidepressant with those taking both an antidepressant and an NSAID.

Of the 409 subjects who took an NSAID and an antidepressant, 182 people, or 45 per cent, were in remission.

In comparison, 628 of the 1,137 people who were on SSRIs alone, or 55 per cent, were in remission — a difference the researchers say is statistically significant or unlikely to be due to chance alone.

Interactions in brain

The data suggest that treatment with NSAIDs prevents clinical responses to antidepressants, the researchers said.

"Many elderly individuals suffering from depression also have arthritic or related diseases and as a consequence are taking both antidepressant and anti-inflammatory medications," Greengard said in a release. "Our results suggest that physicians should carefully balance the advantages and disadvantages of continuing anti-inflammatory therapy in patients being treated with antidepressant medications."

People taking antidepressants are advised to discuss their individual circumstances with their doctor.

The researchers also pointed out it is possible that people who have underlying painful conditions that require taking NSAIDs such as ibuprofen or Aspirin may simply take longer to recover fully from depression, regardless of the combination of drugs.

Since the clinical analysis was done after the fact, it would help to evaluate the effects of NSAIDs and other analgesic painkillers on SSRI antidepressant responses in a double-blind, randomized clinical study, with standardized medications, to better evaluate their role.

More research is also needed to try to understand how the interactions might occur in the brain. The mice findings focused on the frontal cortex, an area of the brain strongly linked to antidepressant response in both the laboratory animals and humans, but the drugs may interact differently in different parts of the brain.

The study was supported by grants from the Skirball Foundation, U.S. Army Medical Research Acquisition Activity, the National Institutes of Health and the Fisher Center for Alzheimer's Disease Foundation.