Certain painkillers, such as ibuprofen and ASA, may interfere with antidepressant medications, blunting their effects, suggests new research that could help explain why many people fail to respond to the drugs.
The research was conducted on both mice and humans and was not comprehensive enough to prove that non-steroidal anti-inflammatory painkillers, or NSAIDs, stop antidepressants from working, the authors said. Still, they bear further research, they write in Proceedings of the National Academy of Sciences, or PNAS.
Scientists at the Fisher Center for Alzheimer's Disease Research at The Rockefeller University, first treated mice with a class of antidepressants called selective serotonin reuptake inhibitors, or SSRIs. Some of the mice were taking the anti-inflammatory painkiller ibuprofen and some weren't.
They then examined how the mice behaved in tasks that are sensitive to antidepressant treatment. They found that the mice given painkillers and antidepressants did worse on tests measuring their stress and depression than those that weren't taking painkillers.
As well, by analyzing the brains of mice treated with an SSRI medication called Celexa, the researchers found that those given an NSAID had lower levels of the Celexa in their blood than those that were only given the antidepressant.
They then tested the findings in humans. They examined data from an already-completed clinical trial of 4,000 depressed patients, focusing on 1,500 of so of them, and found that those who reported taking anti-inflammatory drugs were much less likely to have their symptoms relieved by an antidepressant than patients who reported no NSAID use.
Among those not taking painkillers, 54 per cent of patients said they were responding to their antidepressants at 12 weeks. But that rate dropped to 45 per cent for those who reported using anti-inflammatory agents.
The researchers note that some of the patients took an NSAID only once or twice during the 12 weeks, while others regularly took NSAIDs, and they weren't able to distinguish between the groups.
Dr. Jennifer Warner-Schmidt, who helped lead the research, said it's not clear why NSAIDs might affect antidepressant efficacy.
"Nevertheless, our results may have profound implications for patients, given the very high treatment resistance rates for depressed individuals taking SSRIs," she said in a statement.
The researchers say their finding surprised them, but may help explain why so many depressed patients taking SSRIs do not respond to antidepressant treatment.
The study may be especially significant in the case of Alzheimer's patients, who commonly suffer from depression.
"Many elderly individuals suffering from depression also have arthritic or related diseases and as a consequence are taking both antidepressant and anti-inflammatory medications," noted another of the study's authors, Dr. Paul Greengard.
"Our results suggest that physicians should carefully balance the advantages and disadvantages of continuing anti-inflammatory therapy in patients being treated with antidepressant medications."
The Rockefeller researchers now plan to carry out a study that follows SSRI users over time, rather than looking back at data already completed.
