Eli Lilly has secured another approval from regulators in the USA for its blockbuster antidepressant Cymbalta, this time for chronic musculoskeletal pain.

The US Food and Drug Administration has approved Cymbalta (duloxetine) for the management of chronic musculoskeletal pain, including discomfort from osteoarthritis and chronic lower back pain.This is the fifth indication the agency has granted for the drug which was first used to treat major depressive disorder in 2004.

Cymbalta was approved for diabetic peripheral neuropathy in that same year, followed by green lights for generalised anxiety disorder and maintenance treatment of major depression in 2007 and fibromyalgia in 2008. It is already used 'off-label' for a range of conditions such as musculoskeletal problems, headaches and nerve pain, noted the FDA, which assessed the efficacy of Cymbalta in chronic low back pain and osteoarthritis in four trials involving 600 patients. At the end of the study period, patients taking Cymbalta had a significantly greater pain reduction compared with placebo.

The approval comes after the FDA's Anesthetic and Life Support Drugs Advisory Committee voted 8-5 in favour of expanding the pain indication but 4-9 against supporting its use to treat osteoarthritis, concerned about the known serious side effects associated with the drug. These include liver damage, allergic reactions, pneumonia, depressed mood, suicide and suicidal thoughts.

However the FDA notes that these effects have occurred in less than 1% of treated patients (about 30 million patients in the USA have used Cymbalta) and "there are a finite number of drugs available for the treatment of chronic musculoskeletal pain, all of which are associated with rare, serious side effects".

Janet Woodcock, director of FDA’s Center for Drug Evaluation and Research, said that "up to three quarters of the population experience chronic pain at some time in their lives". She added that “this approval means that many of those people now have another treatment option".

Analysts are unsure as to how much of a boost Cymbalta revenues will get thanks to the new approval, given its already considerable off-label use. Seamus Fernandez at Leerink Swann & Co believes sales may increase by around $500 million.

Sales of Cymbalta in the third quarter rose 4% to $825.3 million.