The thyroid hormone, triiodothyronine (T3), is used as a supplement to antidepressant treatment of major depression, to accelerate and enhance response and as an augmenter in patients who have not responded. While there is support from controlled trials and meta-analyses for the use of T3 in conjunction with tricyclic antidepressants, the evidence base for supplementation of specific serotonin reuptake inhibitors (SSRIs) with T3 is more limited. We reviewed the available literature on T3

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... entation of SSRIs including open-label studies and randomized controlled trials (RCTs). Five RCTs were identified. Three were enhancement studies in which T3 was administered concurrently with the antidepressant from the start of treatment and two were augmentation studies in which T3 was added to the antidepressant treatment of patients who had not responded. Three open augmentation studies were identified. The RCTs were too disparate in methodology to allow a meta-analysis to be performed. The enhancement studies are inconclusive in that one showed strongly positive effects of T3, one showed no effect and one showed a trend. The open augmentation studies supported an effect of T3 in SSRI non-responsive patients with some support from a large RCT; a smaller, underpowered RCT did not show efficacy. T3 was well tolerated in most of the studies and adverse effects do not seem to be an impediment to clinical use. Some of the studies identified clinical and thyroid function correlates of response that require further investigation. Further research is needed before it can be definitively established whether T3 is an effective supplement to SSRIs in patients with MDD. The appropriate timing of T3 supplementation needs to be explored and also the dose and length of treatment.