Researchers Matthew J. Bair, M.D., formerly of the Regenstrief Institute, and colleagues uncovered the connection by analyzing the results of a clinical trial of 573 depression patients taking medications like Prozac, Paxil or Zoloft. Their findings are published in the journal Psychosomatic Medicine.
Although depression improved in most of the patients after three months of drug therapy, 24 percent had persistently high depression scores. The therapy was most likely to fail among those who reported moderate to severe pain at the beginning of their treatment.
"In particular, the odds of a poor depression treatment response were twice as high in patients with moderate pain at baseline and three to four times as high in those with severe pain," Bair says.
Factors like pain may help explain why antidepressants have a mixed record of success, Bair says. Between 50 and 70 percent of depressed patients find only partial relief with their medications.
Researchers have long known that pain and depression often go hand in hand, but there are few studies of how pain might affect depression treatment. In the Bair study, more than two-thirds of the patients reported some degree of pain at the start of their treatment. Twenty-five percent said their pain was mild, 30 percent had moderate pain and 14 percent said they had severe pain.
"We believe a treatment model that incorporates assessment and treatment of both depression and pain is desirable," Bair says.