Concurrent treatment of chronic pain, depression, anxiety and occupational injuries is associated with large increases in total workers compensation claim cost and delayed return to work, according to a study authored by the chief medical officer for AF Group, which released the findings Monday.

Published in the latest Journal of Occupational and Environmental Medicine, the study examined the impact of anti-anxiety benzodiazepines and antidepressants in combination with opioids on workers comp claim cost and closure rates, according to a statement from AF Group. To gather data, researchers with Lansing, Michigan-based AF Group and the Johns Hopkins University School of Medicine in Baltimore analyzed 22,383 work-related indemnity claims from 2008-2013 that had three years maturity in Michigan from AF Group brands, the company said.

Results showed that the slowest claim closure rate — 58.3% in that time period — occurred among claimants with prescriptions for all three types of medications. Claims with both opioid and antidepressant prescriptions closed at a rate of 64.8%. The group without any medications had the highest closure rate at 91.8%, followed by the group with only opioid prescriptions at 89.1%.

Even when controlling for age, chronic pain, medical complexity and claim development in terms of years, antidepressant claims were more likely to remain open at the end of the five-year study period, according to AF Group.

“The overall direction of our findings was expected — injured workers who are experiencing a significant amount of pain or suffering from depression or anxiety will require more medical services than injured workers not experiencing such symptoms or psychosocial disorders,” said Dr. Dan Hunt, medical director at AF Group, in the statement. ”What did surprise us is the increased recovery time and medical costs associated with antidepressant medications.”