BACKGROUND This study was designed to establish whether (as suggested in a number of open and relatively small controlled trials) lithium augmentation is more effective than continued antidepressant alone, where response to a standard course of antidepressant treatment has been absent or partial.

METHOD Lithium or placebo was added on a double-blind basis for six weeks to the drug regime of 62 patients with major depressive illness (in both hospital and primary care settings) who had failed to respond to a controlled trial of fluoxetine or lofepramine. Response was defined as a final Hamilton Depression Rating Scale (HDRS) score of < 10.

RESULTS Response was seen more frequently in patients taking lithium (15/29) than in those remaining on antidepressant alone (8/32; P < 0.05). Rapid response to lithium augmentation (LA) was not consistently observed in this cohort. Mean HDRS scores after six weeks were significantly lower (P < 0.01) in the lithium group after excluding those who had not achieved significant exposure to lithium (arbitrarily defined as two or more lithium levels > or = 0.4 mmol/l). No differences in the efficacy of LA were apparent between fluoxetine and lofepramine.

CONCLUSIONS Our results confirm that LA is a useful strategy in the treatment of antidepressant-resistant depression. Partial response was, however, frequently observed with continued antidepressant treatment alone, and the superiority of LA appears to depend on achieving adequate serum lithium levels.