That depends on which study you read and what kind of back pain you have.
In a review of 10 studies on back pain and antidepressants published recently by the Cochrane Collaboration, an international organization that reviews medical studies, Australian researchers found no clear evidence that antidepressants are more effective than sugar pills in helping patients with low-back pain. The finding is somewhat perplexing because, as the Australian researchers themselves noted, there is evidence that antidepressants can help with other types of chronic pain.