Long-term use of opioid pain medicine significantly raises the risk of developing major depression, according to a large new study of U.S. veterans.
Researchers at Saint Louis University studied the medical records of nearly 50,000 veterans who had no history of opioid use or depression, but were subsequently prescribed opioid painkillers.
They found that patients who remained on opioids for 180 days or longer had a 53% increased risk of developing depression compared to patients who never took opioids. Those who used opioids for 90 to 180 days had a 25% greater risk of becoming depressed. The study is being published in Journal of General Internal Medicine.
“These findings suggest that the longer one is exposed to opioid analgesics, the greater is their risk of developing depression,” said Jeffrey Scherrer, PhD, an associate professor of family and community medicine at Saint Louis University and principle investigator of the study.
“Opioids have long been known to allay pain and suffering, but reports of adverse effects are abundant and continue to emerge.”
Scherrer says there is no clear evidence about the mechanism in which opioids may contribute to depression, but there could be several factors that lead to it.
One possibility is that opioids reset the brain’s “reward pathway” to a higher level, elevating the threshold for a person’s ability to experience pleasure from natural rewards such as a food or sex.
Other factors may be side effects from opioids such as adrenal, testosterone and other hormonal changes, or vitamin D and blood glucose deficiencies.
Scherrer says the higher the dose of opioid analgesics, the greater the risk of depression.
“Preliminary evidence suggests that if you can keep your daily dose low, you may be at lower risk for depression,” he said.
Recent studies indicate that the use of prescription opioid pain medicine has quintupled recently. More than 200 million opioid prescriptions were issued to patients in 2009 in the US.
“Even though the risk is not huge, there is enough exposure that we may have a public health problem,” said Scherrer, adding that patients initiating opioid treatment should be monitored for development of depression.
Many previous studies have found a link between chronic pain and depression, with and without the use of opioids.
A recent study by researchers at the University of Toronto found that people who suffer from migraines are about twice as likely to be depressed and have suicidal thoughts. Women and young people with migraines are particularly vulnerable to what Winston Churchill has called “the black dog” of depression.