As some cancer patients turn to medical marijuana to help ease the pain of chemotherapy, many others must make an awful choice between pain and the benefits of treatment.

As many as 20 to 40 percent of chemotherapy patients report pain lasting months to years, with no pharmaceutical drug on the market indicated for treating the issue.

A new study published yesterday in the Journal of the American Medical Association, however, shows that antidepressants presently on the market help to ease pain associated with chemotherapy, meaning doctors may at any time prescribe the drugs "off-label" for the pain.

"Treating painful chemotherapy-induced peripheral neuropathy is critical," said Ellen M. Lavoie Smith, of the University of Michigan, who led the study. "In some cases, physicians must reduce the patient's chemotherapy dose when the pain becomes too severe. This is not just about improving quality of life by decreasing pain but potentially it's helping patients live longer because they can get their full chemotherapy treatment."

Smith said patients sometimes face a "terrible trade-off": To endure the pain or give up potentially life-saving therapy.

In the study, investigators found that duloxetine eased pain over five weeks compared to placebo, after reporting no easement of pain from paclitaxel or oxaliplatin.

The antidepressant drug is used to treat depression and generalized anxiety disorder but is also used by prescribers to treat pain and tingling in patients with diabetic neuropathy, in addition to muscle and bone pain associated with osteoporosis. The recent findings bolster evidence from several phase-3 studies showing dual reuptake inhibitors to be effective in treating neuropathetic pain.

Investigators said that patients taking the antidepressant reported not only easement of pain but a better quality of life overall, perhaps relating to other indications for the drug.