[The use of thyroid hormones in the treatment of depression]

In treating depression pharmacologically we encounter a delay in the onset of therapeutic action and low response and remission rates. Several modes of intervention are available to accelerate and increase therapeutic response and these are at the forefront of research. Thyroid hormones, particularly triiodothyronine (T3), have been in use for several decades as accelerators and augmenters of antidepressant response. The use of thyroid hormones to supplement antidepressants is based on evidence supporting a bidirectional connection between thyroid function and depression. In patients suffering from depression, higher than expected rates of subclinical hypothyroidism have been found. Furthermore, primary hypothyroidism can be associated with mood disturbances, mainly depression, and a reduced response to antidepressants. The hypothalamic-pituitary-thyroid axis is responsible for the maintenance of homeostasis of body metabolism. The hormones, enzymes responsible for hormone synthesis and degradation, transporters and receptors that are part of this system, are all potential loci for dysfunction and intervention. In this review, the authors present evidence supporting the use of thyroid hormones in the treatment of depression. The studies support the use of T3 in the acceleration and augmentation of tricyclic antidepressants and its augmenting effect on SSRI's. It appears that there may be a sub-group of depressed patients with specific demographic, clinical and genetic characteristic who may benefit specifically from the use of T3. Less evidence is available to support the use of thyroxine (T4).