IPT's original target diagnosis was major depressive disorder without psychotic symptoms among adult outpatients. This section deals with its adaptation and efficacy for mood disorders. IPT was first developed in a continuation study treating patients recovering on medication from an acute depressive episode (see Chapter 10). Like many therapies that have demonstrated efficacy in one area, IPT has since been tested for alternative, "off-label" indications. Successful treatments are commonly extended to new diagnostic indications. Compare, for example, the use of anticonvulsant medications for the treatment of bipolar disorder; the spread of serotonin reuptake inhibitors from their initial application, major depression, to dysthymic disorder, obsessive compulsive disorder, bulimia, and other psychiatric syndromes; of beta-blockers from their original cardiovascular indications to social phobia and explosive disorders; or of cognitive behavioral therapy (CBT) from major depression to panic disorder, bulimia, and other conditions.
Usually there are theoretical reasons for expecting the treatment to work in a new area. In the pharmacotherapy of bipolar disorder, "kindling" theory justified the testing of anticonvulsant medications ( Post et al., 1986). The spread of IPT probably reflects several factors. First, IPT has been proven to have efficacy for major depression. Second, CBT, similarly researched and proven, was being successfully extended to other indications. Third, patients and therapists seem to find the focus of IPT on the relationship between affective state and environment a coherent, reasonable approach to psychiatric syndromes. This linkage of emotion and environment provides an essentially ubiquitous tool for treatment of psychiatric syndromes. How important that link is, and its efficacy as a treatment strategy, may of course vary from syndrome to syndrome.