The patient has bipolar disorder and is not taking any proven mood stabilizers (lithium, lamotrigine, divalproex, or carbamazepine) but has subsyndromal depressive symptoms.
In this case I would begin one of those proven mood stabilizers; following APA treatment guidelines (2) and randomized evidence, one might lean toward lithium or lamotrigine. If, as is frequently the case, the patient is taking other medications such as antidepressants and/or antipsychotics, I would also recommend discontinuing those agents and simply instituting a single proven mood stabilizer as above. This recommendation may seem counterintuitive because anti-depressants are supposed to treat depression and some antipsychotics, like quetiapine, are now indicated for bipolar depression (3). But all such data are for the acute phase, i.e., for about 2 months of treatment when the patient is currently depressed. Usually the scenario is that the patient was acutely depressed 9 months ago, received treatment such as quetiapine plus citalopram [or another serotonin reuptake inhibitor (SRI)], improved partially, and now has chronic subsyndromal depression. None of these agents, in contrast to lamotrigine or lithium or even divalproex, have been shown to have long-term benefits in the prevention (as opposed to treatment) of depressive symptoms in bipolar disorder. Most antipsychotics have simply not been studied in maintenance treatment of bipolar disorder, and those that have been studied, such as olanzapine or aripiprazole (despite Food and Drug Administration indications), have not clearly been shown to be beneficial in depression prevention. Antidepressants, in contrast, have repeatedly been studied and have failed to have preventive benefits for depression in bipolar disorder (4). Most of the data are for tricyclic antidepressants, but randomized data for SRIs are emerging, which suggest either little or no long-term benefit for depression prevention (5). In other words, both antidepressants and antipsychotics seem to have short-term but not long-term benefits. One needs to use the proven mood stabilizers for long-term benefits.